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// Copyright 2021 Google LLC
// SPDX-License-Identifier: Apache-2.0
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Normal include guard for target-independent parts
#ifndef HIGHWAY_HWY_CONTRIB_SORT_VQSORT_INL_H_
#define HIGHWAY_HWY_CONTRIB_SORT_VQSORT_INL_H_
// unconditional #include so we can use if(VQSORT_PRINT), which unlike #if does
// not interfere with code-folding.
#include <stdio.h>
#include <time.h> // clock
// IWYU pragma: begin_exports
#include "hwy/base.h"
#include "hwy/contrib/sort/order.h" // SortAscending
// IWYU pragma: end_exports
#include "hwy/cache_control.h" // Prefetch
#include "hwy/print.h" // unconditional, see above.
// If 1, VQSortStatic can be called without including vqsort.h, and we avoid
// any DLLEXPORT. This simplifies integration into other build systems, but
// decreases the security of random seeds.
#ifndef VQSORT_ONLY_STATIC
#define VQSORT_ONLY_STATIC 0
#endif
// Verbosity: 0 for none, 1 for brief per-sort, 2+ for more details.
#ifndef VQSORT_PRINT
#define VQSORT_PRINT 0
#endif
#if !VQSORT_ONLY_STATIC
#include "hwy/contrib/sort/vqsort.h" // Fill16BytesSecure
#endif
namespace hwy {
namespace detail {
HWY_INLINE void Fill16BytesStatic(void* bytes) {
#if !VQSORT_ONLY_STATIC
if (Fill16BytesSecure(bytes)) return;
#endif
uint64_t* words = reinterpret_cast<uint64_t*>(bytes);
// Static-only, or Fill16BytesSecure failed. Get some entropy from the
// stack/code location, and the clock() timer.
uint64_t** seed_stack = &words;
void (*seed_code)(void*) = &Fill16BytesStatic;
const uintptr_t bits_stack = reinterpret_cast<uintptr_t>(seed_stack);
const uintptr_t bits_code = reinterpret_cast<uintptr_t>(seed_code);
const uint64_t bits_time = static_cast<uint64_t>(clock());
words[0] = bits_stack ^ bits_time ^ 0xFEDCBA98; // "Nothing up my sleeve"
words[1] = bits_code ^ bits_time ^ 0x01234567; // constants.
}
HWY_INLINE uint64_t* GetGeneratorStateStatic() {
thread_local uint64_t state[3] = {0};
// This is a counter; zero indicates not yet initialized.
if (HWY_UNLIKELY(state[2] == 0)) {
Fill16BytesStatic(state);
state[2] = 1;
}
return state;
}
} // namespace detail
} // namespace hwy
#endif // HIGHWAY_HWY_CONTRIB_SORT_VQSORT_INL_H_
// Per-target
#if defined(HIGHWAY_HWY_CONTRIB_SORT_VQSORT_TOGGLE) == \
defined(HWY_TARGET_TOGGLE)
#ifdef HIGHWAY_HWY_CONTRIB_SORT_VQSORT_TOGGLE
#undef HIGHWAY_HWY_CONTRIB_SORT_VQSORT_TOGGLE
#else
#define HIGHWAY_HWY_CONTRIB_SORT_VQSORT_TOGGLE
#endif
#if VQSORT_PRINT
#include "hwy/print-inl.h"
#endif
#include "hwy/contrib/algo/copy-inl.h"
#include "hwy/contrib/sort/shared-inl.h"
#include "hwy/contrib/sort/sorting_networks-inl.h"
#include "hwy/contrib/sort/traits-inl.h"
#include "hwy/contrib/sort/traits128-inl.h"
// Placeholder for internal instrumentation. Do not remove.
#include "hwy/highway.h"
HWY_BEFORE_NAMESPACE();
namespace hwy {
namespace HWY_NAMESPACE {
namespace detail {
using Constants = hwy::SortConstants;
// Wrapper avoids #if in user code (interferes with code folding)
template <class D>
HWY_INLINE void MaybePrintVector(D d, const char* label, Vec<D> v,
size_t start = 0, size_t max_lanes = 16) {
#if VQSORT_PRINT >= 2 // Print is only defined #if
Print(d, label, v, start, max_lanes);
#else
(void)d;
(void)label;
(void)v;
(void)start;
(void)max_lanes;
#endif
}
// ------------------------------ HeapSort
template <class Traits, typename T>
void SiftDown(Traits st, T* HWY_RESTRICT lanes, const size_t num_lanes,
size_t start) {
constexpr size_t N1 = st.LanesPerKey();
const FixedTag<T, N1> d;
while (start < num_lanes) {
const size_t left = 2 * start + N1;
const size_t right = 2 * start + 2 * N1;
if (left >= num_lanes) break;
size_t idx_larger = start;
const auto key_j = st.SetKey(d, lanes + start);
if (AllTrue(d, st.Compare(d, key_j, st.SetKey(d, lanes + left)))) {
idx_larger = left;
}
if (right < num_lanes &&
AllTrue(d, st.Compare(d, st.SetKey(d, lanes + idx_larger),
st.SetKey(d, lanes + right)))) {
idx_larger = right;
}
if (idx_larger == start) break;
st.Swap(lanes + start, lanes + idx_larger);
start = idx_larger;
}
}
// Heapsort: O(1) space, O(N*logN) worst-case comparisons.
// Based on LLVM sanitizer_common.h, licensed under Apache-2.0.
template <class Traits, typename T>
void HeapSort(Traits st, T* HWY_RESTRICT lanes, const size_t num_lanes) {
constexpr size_t N1 = st.LanesPerKey();
if (num_lanes < 2 * N1) return;
// Build heap.
for (size_t i = ((num_lanes - N1) / N1 / 2) * N1; i != (~N1 + 1); i -= N1) {
SiftDown(st, lanes, num_lanes, i);
}
for (size_t i = num_lanes - N1; i != 0; i -= N1) {
// Swap root with last
st.Swap(lanes + 0, lanes + i);
// Sift down the new root.
SiftDown(st, lanes, i, 0);
}
}
#if VQSORT_ENABLED || HWY_IDE
// ------------------------------ BaseCase
// Special cases where `num_lanes` is in the specified range (inclusive).
template <class Traits, typename T>
HWY_INLINE void Sort2To2(Traits st, T* HWY_RESTRICT keys, size_t num_lanes,
T* HWY_RESTRICT /* buf */) {
constexpr size_t kLPK = st.LanesPerKey();
const size_t num_keys = num_lanes / kLPK;
HWY_DASSERT(num_keys == 2);
HWY_ASSUME(num_keys == 2);
// One key per vector, required to avoid reading past the end of `keys`.
const CappedTag<T, kLPK> d;
using V = Vec<decltype(d)>;
V v0 = LoadU(d, keys + 0x0 * kLPK);
V v1 = LoadU(d, keys + 0x1 * kLPK);
Sort2(d, st, v0, v1);
StoreU(v0, d, keys + 0x0 * kLPK);
StoreU(v1, d, keys + 0x1 * kLPK);
}
template <class Traits, typename T>
HWY_INLINE void Sort3To4(Traits st, T* HWY_RESTRICT keys, size_t num_lanes,
T* HWY_RESTRICT buf) {
constexpr size_t kLPK = st.LanesPerKey();
const size_t num_keys = num_lanes / kLPK;
HWY_DASSERT(3 <= num_keys && num_keys <= 4);
HWY_ASSUME(num_keys >= 3);
HWY_ASSUME(num_keys <= 4); // reduces branches
// One key per vector, required to avoid reading past the end of `keys`.
const CappedTag<T, kLPK> d;
using V = Vec<decltype(d)>;
// If num_keys == 3, initialize padding for the last sorting network element
// so that it does not influence the other elements.
Store(st.LastValue(d), d, buf);
// Points to a valid key, or padding. This avoids special-casing
// HWY_MEM_OPS_MIGHT_FAULT because there is only a single key per vector.
T* in_out3 = num_keys == 3 ? buf : keys + 0x3 * kLPK;
V v0 = LoadU(d, keys + 0x0 * kLPK);
V v1 = LoadU(d, keys + 0x1 * kLPK);
V v2 = LoadU(d, keys + 0x2 * kLPK);
V v3 = LoadU(d, in_out3);
Sort4(d, st, v0, v1, v2, v3);
StoreU(v0, d, keys + 0x0 * kLPK);
StoreU(v1, d, keys + 0x1 * kLPK);
StoreU(v2, d, keys + 0x2 * kLPK);
StoreU(v3, d, in_out3);
}
#if HWY_MEM_OPS_MIGHT_FAULT
template <size_t kRows, size_t kLanesPerRow, class D, class Traits,
typename T = TFromD<D>>
HWY_INLINE void CopyHalfToPaddedBuf(D d, Traits st, T* HWY_RESTRICT keys,
size_t num_lanes, T* HWY_RESTRICT buf) {
constexpr size_t kMinLanes = kRows / 2 * kLanesPerRow;
// Must cap for correctness: we will load up to the last valid lane, so
// Lanes(dmax) must not exceed `num_lanes` (known to be at least kMinLanes).
const CappedTag<T, kMinLanes> dmax;
const size_t Nmax = Lanes(dmax);
HWY_DASSERT(Nmax < num_lanes);
HWY_ASSUME(Nmax <= kMinLanes);
// Fill with padding - last in sort order, not copied to keys.
const Vec<decltype(dmax)> kPadding = st.LastValue(dmax);
// Rounding down allows aligned stores, which are typically faster.
size_t i = num_lanes & ~(Nmax - 1);
HWY_ASSUME(i != 0); // because Nmax <= num_lanes; avoids branch
do {
Store(kPadding, dmax, buf + i);
i += Nmax;
// Initialize enough for the last vector even if Nmax > kLanesPerRow.
} while (i < (kRows - 1) * kLanesPerRow + Lanes(d));
// Ensure buf contains all we will read, and perhaps more before.
ptrdiff_t end = static_cast<ptrdiff_t>(num_lanes);
do {
end -= static_cast<ptrdiff_t>(Nmax);
StoreU(LoadU(dmax, keys + end), dmax, buf + end);
} while (end > static_cast<ptrdiff_t>(kRows / 2 * kLanesPerRow));
}
#endif // HWY_MEM_OPS_MIGHT_FAULT
template <size_t kKeysPerRow, class Traits, typename T>
HWY_NOINLINE void Sort8Rows(Traits st, T* HWY_RESTRICT keys, size_t num_lanes,
T* HWY_RESTRICT buf) {
// kKeysPerRow <= 4 because 8 64-bit keys implies 512-bit vectors, which
// are likely slower than 16x4, so 8x4 is the largest we handle here.
static_assert(kKeysPerRow <= 4, "");
constexpr size_t kLPK = st.LanesPerKey();
// We reshape the 1D keys into kRows x kKeysPerRow.
constexpr size_t kRows = 8;
constexpr size_t kLanesPerRow = kKeysPerRow * kLPK;
constexpr size_t kMinLanes = kRows / 2 * kLanesPerRow;
HWY_DASSERT(kMinLanes < num_lanes && num_lanes <= kRows * kLanesPerRow);
const CappedTag<T, kLanesPerRow> d;
using V = Vec<decltype(d)>;
V v4, v5, v6, v7;
// At least half the kRows are valid, otherwise a different function would
// have been called to handle this num_lanes.
V v0 = LoadU(d, keys + 0x0 * kLanesPerRow);
V v1 = LoadU(d, keys + 0x1 * kLanesPerRow);
V v2 = LoadU(d, keys + 0x2 * kLanesPerRow);
V v3 = LoadU(d, keys + 0x3 * kLanesPerRow);
#if HWY_MEM_OPS_MIGHT_FAULT
CopyHalfToPaddedBuf<kRows, kLanesPerRow>(d, st, keys, num_lanes, buf);
v4 = LoadU(d, buf + 0x4 * kLanesPerRow);
v5 = LoadU(d, buf + 0x5 * kLanesPerRow);
v6 = LoadU(d, buf + 0x6 * kLanesPerRow);
v7 = LoadU(d, buf + 0x7 * kLanesPerRow);
#endif // HWY_MEM_OPS_MIGHT_FAULT
#if !HWY_MEM_OPS_MIGHT_FAULT || HWY_IDE
(void)buf;
const V vnum_lanes = Set(d, ConvertScalarTo<T>(num_lanes));
// First offset where not all vector are guaranteed valid.
const V kIota = Iota(d, static_cast<T>(kMinLanes));
const V k1 = Set(d, static_cast<T>(kLanesPerRow));
const V k2 = Add(k1, k1);
using M = Mask<decltype(d)>;
const M m4 = Gt(vnum_lanes, kIota);
const M m5 = Gt(vnum_lanes, Add(kIota, k1));
const M m6 = Gt(vnum_lanes, Add(kIota, k2));
const M m7 = Gt(vnum_lanes, Add(kIota, Add(k2, k1)));
const V kPadding = st.LastValue(d); // Not copied to keys.
v4 = MaskedLoadOr(kPadding, m4, d, keys + 0x4 * kLanesPerRow);
v5 = MaskedLoadOr(kPadding, m5, d, keys + 0x5 * kLanesPerRow);
v6 = MaskedLoadOr(kPadding, m6, d, keys + 0x6 * kLanesPerRow);
v7 = MaskedLoadOr(kPadding, m7, d, keys + 0x7 * kLanesPerRow);
#endif // !HWY_MEM_OPS_MIGHT_FAULT
Sort8(d, st, v0, v1, v2, v3, v4, v5, v6, v7);
// Merge8x2 is a no-op if kKeysPerRow < 2 etc.
Merge8x2<kKeysPerRow>(d, st, v0, v1, v2, v3, v4, v5, v6, v7);
Merge8x4<kKeysPerRow>(d, st, v0, v1, v2, v3, v4, v5, v6, v7);
StoreU(v0, d, keys + 0x0 * kLanesPerRow);
StoreU(v1, d, keys + 0x1 * kLanesPerRow);
StoreU(v2, d, keys + 0x2 * kLanesPerRow);
StoreU(v3, d, keys + 0x3 * kLanesPerRow);
#if HWY_MEM_OPS_MIGHT_FAULT
// Store remaining vectors into buf and safely copy them into keys.
StoreU(v4, d, buf + 0x4 * kLanesPerRow);
StoreU(v5, d, buf + 0x5 * kLanesPerRow);
StoreU(v6, d, buf + 0x6 * kLanesPerRow);
StoreU(v7, d, buf + 0x7 * kLanesPerRow);
const ScalableTag<T> dmax;
const size_t Nmax = Lanes(dmax);
// The first half of vectors have already been stored unconditionally into
// `keys`, so we do not copy them.
size_t i = kMinLanes;
HWY_UNROLL(1)
for (; i + Nmax <= num_lanes; i += Nmax) {
StoreU(LoadU(dmax, buf + i), dmax, keys + i);
}
// Last iteration: copy partial vector
const size_t remaining = num_lanes - i;
HWY_ASSUME(remaining < 256); // helps FirstN
SafeCopyN(remaining, dmax, buf + i, keys + i);
#endif // HWY_MEM_OPS_MIGHT_FAULT
#if !HWY_MEM_OPS_MIGHT_FAULT || HWY_IDE
BlendedStore(v4, m4, d, keys + 0x4 * kLanesPerRow);
BlendedStore(v5, m5, d, keys + 0x5 * kLanesPerRow);
BlendedStore(v6, m6, d, keys + 0x6 * kLanesPerRow);
BlendedStore(v7, m7, d, keys + 0x7 * kLanesPerRow);
#endif // !HWY_MEM_OPS_MIGHT_FAULT
}
template <size_t kKeysPerRow, class Traits, typename T>
HWY_NOINLINE void Sort16Rows(Traits st, T* HWY_RESTRICT keys, size_t num_lanes,
T* HWY_RESTRICT buf) {
static_assert(kKeysPerRow <= SortConstants::kMaxCols, "");
constexpr size_t kLPK = st.LanesPerKey();
// We reshape the 1D keys into kRows x kKeysPerRow.
constexpr size_t kRows = 16;
constexpr size_t kLanesPerRow = kKeysPerRow * kLPK;
constexpr size_t kMinLanes = kRows / 2 * kLanesPerRow;
HWY_DASSERT(kMinLanes < num_lanes && num_lanes <= kRows * kLanesPerRow);
const CappedTag<T, kLanesPerRow> d;
using V = Vec<decltype(d)>;
V v8, v9, va, vb, vc, vd, ve, vf;
// At least half the kRows are valid, otherwise a different function would
// have been called to handle this num_lanes.
V v0 = LoadU(d, keys + 0x0 * kLanesPerRow);
V v1 = LoadU(d, keys + 0x1 * kLanesPerRow);
V v2 = LoadU(d, keys + 0x2 * kLanesPerRow);
V v3 = LoadU(d, keys + 0x3 * kLanesPerRow);
V v4 = LoadU(d, keys + 0x4 * kLanesPerRow);
V v5 = LoadU(d, keys + 0x5 * kLanesPerRow);
V v6 = LoadU(d, keys + 0x6 * kLanesPerRow);
V v7 = LoadU(d, keys + 0x7 * kLanesPerRow);
#if HWY_MEM_OPS_MIGHT_FAULT
CopyHalfToPaddedBuf<kRows, kLanesPerRow>(d, st, keys, num_lanes, buf);
v8 = LoadU(d, buf + 0x8 * kLanesPerRow);
v9 = LoadU(d, buf + 0x9 * kLanesPerRow);
va = LoadU(d, buf + 0xa * kLanesPerRow);
vb = LoadU(d, buf + 0xb * kLanesPerRow);
vc = LoadU(d, buf + 0xc * kLanesPerRow);
vd = LoadU(d, buf + 0xd * kLanesPerRow);
ve = LoadU(d, buf + 0xe * kLanesPerRow);
vf = LoadU(d, buf + 0xf * kLanesPerRow);
#endif // HWY_MEM_OPS_MIGHT_FAULT
#if !HWY_MEM_OPS_MIGHT_FAULT || HWY_IDE
(void)buf;
const V vnum_lanes = Set(d, ConvertScalarTo<T>(num_lanes));
// First offset where not all vector are guaranteed valid.
const V kIota = Iota(d, static_cast<T>(kMinLanes));
const V k1 = Set(d, static_cast<T>(kLanesPerRow));
const V k2 = Add(k1, k1);
const V k4 = Add(k2, k2);
const V k8 = Add(k4, k4);
using M = Mask<decltype(d)>;
const M m8 = Gt(vnum_lanes, kIota);
const M m9 = Gt(vnum_lanes, Add(kIota, k1));
const M ma = Gt(vnum_lanes, Add(kIota, k2));
const M mb = Gt(vnum_lanes, Add(kIota, Sub(k4, k1)));
const M mc = Gt(vnum_lanes, Add(kIota, k4));
const M md = Gt(vnum_lanes, Add(kIota, Add(k4, k1)));
const M me = Gt(vnum_lanes, Add(kIota, Add(k4, k2)));
const M mf = Gt(vnum_lanes, Add(kIota, Sub(k8, k1)));
const V kPadding = st.LastValue(d); // Not copied to keys.
v8 = MaskedLoadOr(kPadding, m8, d, keys + 0x8 * kLanesPerRow);
v9 = MaskedLoadOr(kPadding, m9, d, keys + 0x9 * kLanesPerRow);
va = MaskedLoadOr(kPadding, ma, d, keys + 0xa * kLanesPerRow);
vb = MaskedLoadOr(kPadding, mb, d, keys + 0xb * kLanesPerRow);
vc = MaskedLoadOr(kPadding, mc, d, keys + 0xc * kLanesPerRow);
vd = MaskedLoadOr(kPadding, md, d, keys + 0xd * kLanesPerRow);
ve = MaskedLoadOr(kPadding, me, d, keys + 0xe * kLanesPerRow);
vf = MaskedLoadOr(kPadding, mf, d, keys + 0xf * kLanesPerRow);
#endif // !HWY_MEM_OPS_MIGHT_FAULT
Sort16(d, st, v0, v1, v2, v3, v4, v5, v6, v7, v8, v9, va, vb, vc, vd, ve, vf);
// Merge16x4 is a no-op if kKeysPerRow < 4 etc.
Merge16x2<kKeysPerRow>(d, st, v0, v1, v2, v3, v4, v5, v6, v7, v8, v9, va, vb,
vc, vd, ve, vf);
Merge16x4<kKeysPerRow>(d, st, v0, v1, v2, v3, v4, v5, v6, v7, v8, v9, va, vb,
vc, vd, ve, vf);
Merge16x8<kKeysPerRow>(d, st, v0, v1, v2, v3, v4, v5, v6, v7, v8, v9, va, vb,
vc, vd, ve, vf);
#if !HWY_COMPILER_MSVC && !HWY_IS_DEBUG_BUILD
Merge16x16<kKeysPerRow>(d, st, v0, v1, v2, v3, v4, v5, v6, v7, v8, v9, va, vb,
vc, vd, ve, vf);
#endif
StoreU(v0, d, keys + 0x0 * kLanesPerRow);
StoreU(v1, d, keys + 0x1 * kLanesPerRow);
StoreU(v2, d, keys + 0x2 * kLanesPerRow);
StoreU(v3, d, keys + 0x3 * kLanesPerRow);
StoreU(v4, d, keys + 0x4 * kLanesPerRow);
StoreU(v5, d, keys + 0x5 * kLanesPerRow);
StoreU(v6, d, keys + 0x6 * kLanesPerRow);
StoreU(v7, d, keys + 0x7 * kLanesPerRow);
#if HWY_MEM_OPS_MIGHT_FAULT
// Store remaining vectors into buf and safely copy them into keys.
StoreU(v8, d, buf + 0x8 * kLanesPerRow);
StoreU(v9, d, buf + 0x9 * kLanesPerRow);
StoreU(va, d, buf + 0xa * kLanesPerRow);
StoreU(vb, d, buf + 0xb * kLanesPerRow);
StoreU(vc, d, buf + 0xc * kLanesPerRow);
StoreU(vd, d, buf + 0xd * kLanesPerRow);
StoreU(ve, d, buf + 0xe * kLanesPerRow);
StoreU(vf, d, buf + 0xf * kLanesPerRow);
const ScalableTag<T> dmax;
const size_t Nmax = Lanes(dmax);
// The first half of vectors have already been stored unconditionally into
// `keys`, so we do not copy them.
size_t i = kMinLanes;
HWY_UNROLL(1)
for (; i + Nmax <= num_lanes; i += Nmax) {
StoreU(LoadU(dmax, buf + i), dmax, keys + i);
}
// Last iteration: copy partial vector
const size_t remaining = num_lanes - i;
HWY_ASSUME(remaining < 256); // helps FirstN
SafeCopyN(remaining, dmax, buf + i, keys + i);
#endif // HWY_MEM_OPS_MIGHT_FAULT
#if !HWY_MEM_OPS_MIGHT_FAULT || HWY_IDE
BlendedStore(v8, m8, d, keys + 0x8 * kLanesPerRow);
BlendedStore(v9, m9, d, keys + 0x9 * kLanesPerRow);
BlendedStore(va, ma, d, keys + 0xa * kLanesPerRow);
BlendedStore(vb, mb, d, keys + 0xb * kLanesPerRow);
BlendedStore(vc, mc, d, keys + 0xc * kLanesPerRow);
BlendedStore(vd, md, d, keys + 0xd * kLanesPerRow);
BlendedStore(ve, me, d, keys + 0xe * kLanesPerRow);
BlendedStore(vf, mf, d, keys + 0xf * kLanesPerRow);
#endif // !HWY_MEM_OPS_MIGHT_FAULT
}
// Sorts `keys` within the range [0, num_lanes) via sorting network.
// Reshapes into a matrix, sorts columns independently, and then merges
// into a sorted 1D array without transposing.
//
// `TraitsKV` is SharedTraits<Traits*<Order*>>. This abstraction layer bridges
// differences in sort order and single-lane vs 128-bit keys. For key-value
// types, items with the same key are not equivalent. Our sorting network
// does not preserve order, thus we prevent mixing padding into the items by
// comparing all the item bits, including the value (see *ForSortingNetwork).
//
template <class D, class TraitsKV, typename T>
HWY_NOINLINE void BaseCase(D d, TraitsKV, T* HWY_RESTRICT keys,
size_t num_lanes, T* buf) {
using Traits = typename TraitsKV::SharedTraitsForSortingNetwork;
Traits st;
constexpr size_t kLPK = st.LanesPerKey();
HWY_DASSERT(num_lanes <= Constants::BaseCaseNumLanes<kLPK>(Lanes(d)));
const size_t num_keys = num_lanes / kLPK;
// Can be zero when called through HandleSpecialCases, but also 1 (in which
// case the array is already sorted). Also ensures num_lanes - 1 != 0.
if (HWY_UNLIKELY(num_keys <= 1)) return;
const size_t ceil_log2 =
32 - Num0BitsAboveMS1Bit_Nonzero32(static_cast<uint32_t>(num_keys - 1));
// Checking kMaxKeysPerVector avoids generating unreachable codepaths.
constexpr size_t kMaxKeysPerVector = MaxLanes(d) / kLPK;
using FuncPtr = decltype(&Sort2To2<Traits, T>);
const FuncPtr funcs[9] = {
/* <= 1 */ nullptr, // We ensured num_keys > 1.
/* <= 2 */ &Sort2To2<Traits, T>,
/* <= 4 */ &Sort3To4<Traits, T>,
/* <= 8 */ &Sort8Rows<1, Traits, T>, // 1 key per row
/* <= 16 */ kMaxKeysPerVector >= 2 ? &Sort8Rows<2, Traits, T> : nullptr,
/* <= 32 */ kMaxKeysPerVector >= 4 ? &Sort8Rows<4, Traits, T> : nullptr,
/* <= 64 */ kMaxKeysPerVector >= 4 ? &Sort16Rows<4, Traits, T> : nullptr,
/* <= 128 */ kMaxKeysPerVector >= 8 ? &Sort16Rows<8, Traits, T> : nullptr,
#if !HWY_COMPILER_MSVC && !HWY_IS_DEBUG_BUILD
/* <= 256 */ kMaxKeysPerVector >= 16 ? &Sort16Rows<16, Traits, T> : nullptr,
#endif
};
funcs[ceil_log2](st, keys, num_lanes, buf);
}
// ------------------------------ Partition
// Partitions O(1) of the *rightmost* keys, at least `N`, until a multiple of
// kUnroll*N remains, or all keys if there are too few for that.
//
// Returns how many remain to partition at the *start* of `keys`, sets `bufL` to
// the number of keys for the left partition written to `buf`, and `writeR` to
// the start of the finished right partition at the end of `keys`.
template <class D, class Traits, class T>
HWY_INLINE size_t PartitionRightmost(D d, Traits st, T* const keys,
const size_t num, const Vec<D> pivot,
size_t& bufL, size_t& writeR,
T* HWY_RESTRICT buf) {
const size_t N = Lanes(d);
HWY_DASSERT(num > 2 * N); // BaseCase handles smaller arrays
constexpr size_t kUnroll = Constants::kPartitionUnroll;
size_t num_here; // how many to process here
size_t num_main; // how many for main Partition loop (return value)
{
// The main Partition loop increments by kUnroll * N, so at least handle
// the remainders here.
const size_t remainder = num & (kUnroll * N - 1);
// Ensure we handle at least one vector to prevent overruns (see below), but
// still leave a multiple of kUnroll * N.
const size_t min = remainder + (remainder < N ? kUnroll * N : 0);
// Do not exceed the input size.
num_here = HWY_MIN(min, num);
num_main = num - num_here;
// Before the main Partition loop we load two blocks; if not enough left for
// that, handle everything here.
if (num_main < 2 * kUnroll * N) {
num_here = num;
num_main = 0;
}
}
HWY_DASSERT(num_here >= N);
// Postcondition: from here and above belongs to the right partition. Process
// vectors right to left to prevent overrunning `keys` in `StoreLeftRight`,
// which writes up to and including `writeR` via `CompressBlendedStore`,
// which loads and stores a whole vector. This will be safe because we now
// handle at least one vector at the end, which serves as padding.
T* pWriteR = keys + num;
const T* pReadR = pWriteR; // <= pWriteR
bufL = 0; // how much written to buf
size_t i = 0;
// For whole vectors, we can LoadU.
for (; i <= num_here - N; i += N) {
pReadR -= N;
HWY_DASSERT(pReadR >= keys);
const Vec<D> v = LoadU(d, pReadR);
const Mask<D> comp = st.Compare(d, pivot, v);
const size_t numL = CompressStore(v, Not(comp), d, buf + bufL);
bufL += numL;
pWriteR -= (N - numL);
HWY_DASSERT(pWriteR >= pReadR);
(void)CompressBlendedStore(v, comp, d, pWriteR);
}
// Last iteration: avoid reading past the end.
const size_t remaining = num_here - i;
if (HWY_LIKELY(remaining != 0)) {
const Mask<D> mask = FirstN(d, remaining);
pReadR -= remaining;
HWY_DASSERT(pReadR >= keys);
const Vec<D> v = LoadN(d, pReadR, remaining);
const Mask<D> comp = st.Compare(d, pivot, v);
const size_t numL = CompressStore(v, AndNot(comp, mask), d, buf + bufL);
bufL += numL;
pWriteR -= (remaining - numL);
HWY_DASSERT(pWriteR >= pReadR);
(void)CompressBlendedStore(v, And(comp, mask), d, pWriteR);
}
HWY_DASSERT(bufL <= num_here); // wrote no more than read
// MSAN seems not to understand CompressStore. buf[0, bufL) are valid.
detail::MaybeUnpoison(buf, bufL);
writeR = static_cast<size_t>(pWriteR - keys);
const size_t numWrittenR = num - writeR;
(void)numWrittenR; // only for HWY_DASSERT
HWY_DASSERT(numWrittenR <= num_here); // wrote no more than read
// Ensure we finished reading/writing all we wanted
HWY_DASSERT(pReadR == keys + num_main);
HWY_DASSERT(bufL + numWrittenR == num_here);
return num_main;
}
// Note: we could track the OrXor of v and pivot to see if the entire left
// partition is equal, but that happens rarely and thus is a net loss.
template <class D, class Traits, typename T>
HWY_INLINE void StoreLeftRight(D d, Traits st, const Vec<D> v,
const Vec<D> pivot, T* HWY_RESTRICT keys,
size_t& writeL, size_t& remaining) {
const size_t N = Lanes(d);
const Mask<D> comp = st.Compare(d, pivot, v);
// Otherwise StoreU/CompressStore overwrites right keys.
HWY_DASSERT(remaining >= 2 * N);
remaining -= N;
if (hwy::HWY_NAMESPACE::CompressIsPartition<T>::value ||
(HWY_MAX_BYTES == 16 && st.Is128())) {
// Non-native Compress (e.g. AVX2): we are able to partition a vector using
// a single Compress+two StoreU instead of two Compress[Blended]Store. The
// latter are more expensive. Because we store entire vectors, the contents
// between the updated writeL and writeR are ignored and will be overwritten
// by subsequent calls. This works because writeL and writeR are at least
// two vectors apart.
const Vec<D> lr = st.CompressKeys(v, comp);
const size_t num_left = N - CountTrue(d, comp);
StoreU(lr, d, keys + writeL);
// Now write the right-side elements (if any), such that the previous writeR
// is one past the end of the newly written right elements, then advance.
StoreU(lr, d, keys + remaining + writeL);
writeL += num_left;
} else {
// Native Compress[Store] (e.g. AVX3), which only keep the left or right
// side, not both, hence we require two calls.
const size_t num_left = CompressStore(v, Not(comp), d, keys + writeL);
writeL += num_left;
(void)CompressBlendedStore(v, comp, d, keys + remaining + writeL);
}
}
template <class D, class Traits, typename T>
HWY_INLINE void StoreLeftRight4(D d, Traits st, const Vec<D> v0,
const Vec<D> v1, const Vec<D> v2,
const Vec<D> v3, const Vec<D> pivot,
T* HWY_RESTRICT keys, size_t& writeL,
size_t& remaining) {
StoreLeftRight(d, st, v0, pivot, keys, writeL, remaining);
StoreLeftRight(d, st, v1, pivot, keys, writeL, remaining);
StoreLeftRight(d, st, v2, pivot, keys, writeL, remaining);
StoreLeftRight(d, st, v3, pivot, keys, writeL, remaining);
}
// For the last two vectors, we cannot use StoreLeftRight because it might
// overwrite prior right-side keys. Instead write R and append L into `buf`.
template <class D, class Traits, typename T>
HWY_INLINE void StoreRightAndBuf(D d, Traits st, const Vec<D> v,
const Vec<D> pivot, T* HWY_RESTRICT keys,
size_t& writeR, T* HWY_RESTRICT buf,
size_t& bufL) {
const size_t N = Lanes(d);
const Mask<D> comp = st.Compare(d, pivot, v);
const size_t numL = CompressStore(v, Not(comp), d, buf + bufL);
bufL += numL;
writeR -= (N - numL);
(void)CompressBlendedStore(v, comp, d, keys + writeR);
}
// Moves "<= pivot" keys to the front, and others to the back. pivot is
// broadcasted. Returns the index of the first key in the right partition.
//
// Time-critical, but aligned loads do not seem to be worthwhile because we
// are not bottlenecked by load ports.
template <class D, class Traits, typename T>
HWY_INLINE size_t Partition(D d, Traits st, T* const keys, const size_t num,
const Vec<D> pivot, T* HWY_RESTRICT buf) {
using V = decltype(Zero(d));
const size_t N = Lanes(d);
size_t bufL, writeR;
const size_t num_main =
PartitionRightmost(d, st, keys, num, pivot, bufL, writeR, buf);
HWY_DASSERT(num_main <= num && writeR <= num);
HWY_DASSERT(bufL <= Constants::PartitionBufNum(N));
HWY_DASSERT(num_main + bufL == writeR);
if (VQSORT_PRINT >= 3) {
fprintf(stderr, " num_main %zu bufL %zu writeR %zu\n", num_main, bufL,
writeR);
}
constexpr size_t kUnroll = Constants::kPartitionUnroll;
// Partition splits the vector into 3 sections, left to right: Elements
// smaller or equal to the pivot, unpartitioned elements and elements larger
// than the pivot. To write elements unconditionally on the loop body without
// overwriting existing data, we maintain two regions of the loop where all
// elements have been copied elsewhere (e.g. vector registers.). I call these
// bufferL and bufferR, for left and right respectively.
//
// These regions are tracked by the indices (writeL, writeR, left, right) as
// presented in the diagram below.
//
// writeL writeR
// \/ \/
// | <= pivot | bufferL | unpartitioned | bufferR | > pivot |
// \/ \/ \/
// readL readR num
//
// In the main loop body below we choose a side, load some elements out of the
// vector and move either `readL` or `readR`. Next we call into StoreLeftRight
// to partition the data, and the partitioned elements will be written either
// to writeR or writeL and the corresponding index will be moved accordingly.
//
// Note that writeR is not explicitly tracked as an optimization for platforms
// with conditional operations. Instead we track writeL and the number of
// not yet written elements (`remaining`). From the diagram above we can see
// that:
// writeR - writeL = remaining => writeR = remaining + writeL
//
// Tracking `remaining` is advantageous because each iteration reduces the
// number of unpartitioned elements by a fixed amount, so we can compute
// `remaining` without data dependencies.
size_t writeL = 0;
size_t remaining = writeR - writeL;
const T* readL = keys;
const T* readR = keys + num_main;
// Cannot load if there were fewer than 2 * kUnroll * N.
if (HWY_LIKELY(num_main != 0)) {
HWY_DASSERT(num_main >= 2 * kUnroll * N);
HWY_DASSERT((num_main & (kUnroll * N - 1)) == 0);
// Make space for writing in-place by reading from readL/readR.
const V vL0 = LoadU(d, readL + 0 * N);
const V vL1 = LoadU(d, readL + 1 * N);
const V vL2 = LoadU(d, readL + 2 * N);
const V vL3 = LoadU(d, readL + 3 * N);
readL += kUnroll * N;
readR -= kUnroll * N;
const V vR0 = LoadU(d, readR + 0 * N);
const V vR1 = LoadU(d, readR + 1 * N);
const V vR2 = LoadU(d, readR + 2 * N);
const V vR3 = LoadU(d, readR + 3 * N);
// readL/readR changed above, so check again before the loop.
while (readL != readR) {
V v0, v1, v2, v3;
// Data-dependent but branching is faster than forcing branch-free.
const size_t capacityL =
static_cast<size_t>((readL - keys) - static_cast<ptrdiff_t>(writeL));
HWY_DASSERT(capacityL <= num_main); // >= 0
// Load data from the end of the vector with less data (front or back).
// The next paragraphs explain how this works.
//
// let block_size = (kUnroll * N)
// On the loop prelude we load block_size elements from the front of the
// vector and an additional block_size elements from the back. On each
// iteration k elements are written to the front of the vector and
// (block_size - k) to the back.
//
// This creates a loop invariant where the capacity on the front
// (capacityL) and on the back (capacityR) always add to 2 * block_size.
// In other words:
// capacityL + capacityR = 2 * block_size
// capacityR = 2 * block_size - capacityL
//
// This means that:
// capacityL > capacityR <=>
// capacityL > 2 * block_size - capacityL <=>
// 2 * capacityL > 2 * block_size <=>
// capacityL > block_size
if (capacityL > kUnroll * N) { // equivalent to capacityL > capacityR.
readR -= kUnroll * N;
v0 = LoadU(d, readR + 0 * N);
v1 = LoadU(d, readR + 1 * N);
v2 = LoadU(d, readR + 2 * N);
v3 = LoadU(d, readR + 3 * N);
hwy::Prefetch(readR - 3 * kUnroll * N);
} else {
v0 = LoadU(d, readL + 0 * N);
v1 = LoadU(d, readL + 1 * N);
v2 = LoadU(d, readL + 2 * N);
v3 = LoadU(d, readL + 3 * N);
readL += kUnroll * N;
hwy::Prefetch(readL + 3 * kUnroll * N);
}
StoreLeftRight4(d, st, v0, v1, v2, v3, pivot, keys, writeL, remaining);
}
// Now finish writing the saved vectors to the middle.
StoreLeftRight4(d, st, vL0, vL1, vL2, vL3, pivot, keys, writeL, remaining);
StoreLeftRight(d, st, vR0, pivot, keys, writeL, remaining);
StoreLeftRight(d, st, vR1, pivot, keys, writeL, remaining);
// Switch back to updating writeR for clarity. The middle is missing vR2/3
// and what is in the buffer.
HWY_DASSERT(remaining == bufL + 2 * N);
writeR = writeL + remaining;
// Switch to StoreRightAndBuf for the last two vectors because
// StoreLeftRight may overwrite prior keys.
StoreRightAndBuf(d, st, vR2, pivot, keys, writeR, buf, bufL);
StoreRightAndBuf(d, st, vR3, pivot, keys, writeR, buf, bufL);
HWY_DASSERT(writeR <= num); // >= 0
HWY_DASSERT(bufL <= Constants::PartitionBufNum(N));
}
// We have partitioned [0, num) into [0, writeL) and [writeR, num).
// Now insert left keys from `buf` to empty space starting at writeL.
HWY_DASSERT(writeL + bufL == writeR);
CopyBytes(buf, keys + writeL, bufL * sizeof(T));
return writeL + bufL;
}
// Returns true and partitions if [keys, keys + num) contains only {valueL,
// valueR}. Otherwise, sets third to the first differing value; keys may have
// been reordered and a regular Partition is still necessary.
// Called from two locations, hence NOINLINE.
template <class D, class Traits, typename T>
HWY_NOINLINE bool MaybePartitionTwoValue(D d, Traits st, T* HWY_RESTRICT keys,
size_t num, const Vec<D> valueL,
const Vec<D> valueR, Vec<D>& third,
T* HWY_RESTRICT buf) {
const size_t N = Lanes(d);
// No guarantee that num >= N because this is called for subarrays!
size_t i = 0;
size_t writeL = 0;
// As long as all lanes are equal to L or R, we can overwrite with valueL.
// This is faster than first counting, then backtracking to fill L and R.
if (num >= N) {
for (; i <= num - N; i += N) {
const Vec<D> v = LoadU(d, keys + i);
// It is not clear how to apply OrXor here - that can check if *both*
// comparisons are true, but here we want *either*. Comparing the unsigned
// min of differences to zero works, but is expensive for u64 prior to
// AVX3.
const Mask<D> eqL = st.EqualKeys(d, v, valueL);
const Mask<D> eqR = st.EqualKeys(d, v, valueR);
// At least one other value present; will require a regular partition.
// On AVX-512, Or + AllTrue are folded into a single kortest if we are
// careful with the FindKnownFirstTrue argument, see below.
if (HWY_UNLIKELY(!AllTrue(d, Or(eqL, eqR)))) {
// If we repeat Or(eqL, eqR) here, the compiler will hoist it into the
// loop, which is a pessimization because this if-true branch is cold.
// We can defeat this via Not(Xor), which is equivalent because eqL and
// eqR cannot be true at the same time. Can we elide the additional Not?
// FindFirstFalse instructions are generally unavailable, but we can
// fuse Not and Xor/Or into one ExclusiveNeither.
const size_t lane = FindKnownFirstTrue(d, ExclusiveNeither(eqL, eqR));
third = st.SetKey(d, keys + i + lane);
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "found 3rd value at vec %zu; writeL %zu\n", i,
writeL);
}
// 'Undo' what we did by filling the remainder of what we read with R.
if (i >= N) {
for (; writeL <= i - N; writeL += N) {
StoreU(valueR, d, keys + writeL);
}
}
BlendedStore(valueR, FirstN(d, i - writeL), d, keys + writeL);
return false;
}
StoreU(valueL, d, keys + writeL);
writeL += CountTrue(d, eqL);
}
}
// Final vector, masked comparison (no effect if i == num)
const size_t remaining = num - i;
SafeCopyN(remaining, d, keys + i, buf);
const Vec<D> v = Load(d, buf);
const Mask<D> valid = FirstN(d, remaining);
const Mask<D> eqL = And(st.EqualKeys(d, v, valueL), valid);
const Mask<D> eqR = st.EqualKeys(d, v, valueR);
// Invalid lanes are considered equal.
const Mask<D> eq = Or(Or(eqL, eqR), Not(valid));
// At least one other value present; will require a regular partition.
if (HWY_UNLIKELY(!AllTrue(d, eq))) {
const size_t lane = FindKnownFirstTrue(d, Not(eq));
third = st.SetKey(d, keys + i + lane);
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "found 3rd value at partial vec %zu; writeL %zu\n", i,
writeL);
}
// 'Undo' what we did by filling the remainder of what we read with R.
if (i >= N) {
for (; writeL <= i - N; writeL += N) {
StoreU(valueR, d, keys + writeL);
}
}
BlendedStore(valueR, FirstN(d, i - writeL), d, keys + writeL);
return false;
}
BlendedStore(valueL, valid, d, keys + writeL);
writeL += CountTrue(d, eqL);
// Fill right side
i = writeL;
if (num >= N) {
for (; i <= num - N; i += N) {
StoreU(valueR, d, keys + i);
}
}
BlendedStore(valueR, FirstN(d, num - i), d, keys + i);
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Successful MaybePartitionTwoValue\n");
}
return true;
}
// Same as above, except that the pivot equals valueR, so scan right to left.
template <class D, class Traits, typename T>
HWY_INLINE bool MaybePartitionTwoValueR(D d, Traits st, T* HWY_RESTRICT keys,
size_t num, const Vec<D> valueL,
const Vec<D> valueR, Vec<D>& third,
T* HWY_RESTRICT buf) {
const size_t N = Lanes(d);
HWY_DASSERT(num >= N);
size_t pos = num - N; // current read/write position
size_t countR = 0; // number of valueR found
// For whole vectors, in descending address order: as long as all lanes are
// equal to L or R, overwrite with valueR. This is faster than counting, then
// filling both L and R. Loop terminates after unsigned wraparound.
for (; pos < num; pos -= N) {
const Vec<D> v = LoadU(d, keys + pos);
// It is not clear how to apply OrXor here - that can check if *both*
// comparisons are true, but here we want *either*. Comparing the unsigned
// min of differences to zero works, but is expensive for u64 prior to AVX3.
const Mask<D> eqL = st.EqualKeys(d, v, valueL);
const Mask<D> eqR = st.EqualKeys(d, v, valueR);
// If there is a third value, stop and undo what we've done. On AVX-512,
// Or + AllTrue are folded into a single kortest, but only if we are
// careful with the FindKnownFirstTrue argument - see prior comment on that.
if (HWY_UNLIKELY(!AllTrue(d, Or(eqL, eqR)))) {
const size_t lane = FindKnownFirstTrue(d, ExclusiveNeither(eqL, eqR));
third = st.SetKey(d, keys + pos + lane);
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "found 3rd value at vec %zu; countR %zu\n", pos,
countR);
MaybePrintVector(d, "third", third, 0, st.LanesPerKey());
}
pos += N; // rewind: we haven't yet committed changes in this iteration.
// We have filled [pos, num) with R, but only countR of them should have
// been written. Rewrite [pos, num - countR) to L.
HWY_DASSERT(countR <= num - pos);
const size_t endL = num - countR;
if (endL >= N) {
for (; pos <= endL - N; pos += N) {
StoreU(valueL, d, keys + pos);
}
}
BlendedStore(valueL, FirstN(d, endL - pos), d, keys + pos);
return false;
}
StoreU(valueR, d, keys + pos);
countR += CountTrue(d, eqR);
}
// Final partial (or empty) vector, masked comparison.
const size_t remaining = pos + N;
HWY_DASSERT(remaining <= N);
const Vec<D> v = LoadU(d, keys); // Safe because num >= N.
const Mask<D> valid = FirstN(d, remaining);
const Mask<D> eqL = st.EqualKeys(d, v, valueL);
const Mask<D> eqR = And(st.EqualKeys(d, v, valueR), valid);
// Invalid lanes are considered equal.
const Mask<D> eq = Or(Or(eqL, eqR), Not(valid));
// At least one other value present; will require a regular partition.
if (HWY_UNLIKELY(!AllTrue(d, eq))) {
const size_t lane = FindKnownFirstTrue(d, Not(eq));
third = st.SetKey(d, keys + lane);
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "found 3rd value at partial vec %zu; writeR %zu\n", pos,
countR);
MaybePrintVector(d, "third", third, 0, st.LanesPerKey());
}
pos += N; // rewind: we haven't yet committed changes in this iteration.
// We have filled [pos, num) with R, but only countR of them should have
// been written. Rewrite [pos, num - countR) to L.
HWY_DASSERT(countR <= num - pos);
const size_t endL = num - countR;
if (endL >= N) {
for (; pos <= endL - N; pos += N) {
StoreU(valueL, d, keys + pos);
}
}
BlendedStore(valueL, FirstN(d, endL - pos), d, keys + pos);
return false;
}
const size_t lastR = CountTrue(d, eqR);
countR += lastR;
// First finish writing valueR - [0, N) lanes were not yet written.
StoreU(valueR, d, keys); // Safe because num >= N.
// Fill left side (ascending order for clarity)
const size_t endL = num - countR;
size_t i = 0;
if (endL >= N) {
for (; i <= endL - N; i += N) {
StoreU(valueL, d, keys + i);
}
}
Store(valueL, d, buf);
SafeCopyN(endL - i, d, buf, keys + i); // avoids asan overrun
if (VQSORT_PRINT >= 2) {
fprintf(stderr,
"MaybePartitionTwoValueR countR %zu pos %zu i %zu endL %zu\n",
countR, pos, i, endL);
}
return true;
}
// `idx_second` is `first_mismatch` from `AllEqual` and thus the index of the
// second key. This is the first path into `MaybePartitionTwoValue`, called
// when all samples are equal. Returns false if there are at least a third
// value and sets `third`. Otherwise, partitions the array and returns true.
template <class D, class Traits, typename T>
HWY_INLINE bool PartitionIfTwoKeys(D d, Traits st, const Vec<D> pivot,
T* HWY_RESTRICT keys, size_t num,
const size_t idx_second, const Vec<D> second,
Vec<D>& third, T* HWY_RESTRICT buf) {
// True if second comes before pivot.
const bool is_pivotR = AllFalse(d, st.Compare(d, pivot, second));
if (VQSORT_PRINT >= 1) {
fprintf(stderr, "Samples all equal, diff at %zu, isPivotR %d\n", idx_second,
is_pivotR);
}
HWY_DASSERT(AllFalse(d, st.EqualKeys(d, second, pivot)));
// If pivot is R, we scan backwards over the entire array. Otherwise,
// we already scanned up to idx_second and can leave those in place.
return is_pivotR ? MaybePartitionTwoValueR(d, st, keys, num, second, pivot,
third, buf)
: MaybePartitionTwoValue(d, st, keys + idx_second,
num - idx_second, pivot, second,
third, buf);
}
// Second path into `MaybePartitionTwoValue`, called when not all samples are
// equal. `samples` is sorted.
template <class D, class Traits, typename T>
HWY_INLINE bool PartitionIfTwoSamples(D d, Traits st, T* HWY_RESTRICT keys,
size_t num, T* HWY_RESTRICT samples) {
constexpr size_t kSampleLanes = Constants::SampleLanes<T>();
constexpr size_t N1 = st.LanesPerKey();
const Vec<D> valueL = st.SetKey(d, samples);
const Vec<D> valueR = st.SetKey(d, samples + kSampleLanes - N1);
HWY_DASSERT(AllTrue(d, st.Compare(d, valueL, valueR)));
HWY_DASSERT(AllFalse(d, st.EqualKeys(d, valueL, valueR)));
const Vec<D> prev = st.PrevValue(d, valueR);
// If the sample has more than two values, then the keys have at least that
// many, and thus this special case is inapplicable.
if (HWY_UNLIKELY(!AllTrue(d, st.EqualKeys(d, valueL, prev)))) {
return false;
}
// Must not overwrite samples because if this returns false, caller wants to
// read the original samples again.
T* HWY_RESTRICT buf = samples + kSampleLanes;
Vec<D> third; // unused
return MaybePartitionTwoValue(d, st, keys, num, valueL, valueR, third, buf);
}
// ------------------------------ Pivot sampling
template <class Traits, class V>
HWY_INLINE V MedianOf3(Traits st, V v0, V v1, V v2) {
const DFromV<V> d;
// Slightly faster for 128-bit, apparently because not serially dependent.
if (st.Is128()) {
// Median = XOR-sum 'minus' the first and last. Calling First twice is
// slightly faster than Compare + 2 IfThenElse or even IfThenElse + XOR.
const V sum = Xor(Xor(v0, v1), v2);
const V first = st.First(d, st.First(d, v0, v1), v2);
const V last = st.Last(d, st.Last(d, v0, v1), v2);
return Xor(Xor(sum, first), last);
}
st.Sort2(d, v0, v2);
v1 = st.Last(d, v0, v1);
v1 = st.First(d, v1, v2);
return v1;
}
HWY_INLINE uint64_t RandomBits(uint64_t* HWY_RESTRICT state) {
const uint64_t a = state[0];
const uint64_t b = state[1];
const uint64_t w = state[2] + 1;
const uint64_t next = a ^ w;
state[0] = (b + (b << 3)) ^ (b >> 11);
const uint64_t rot = (b << 24) | (b >> 40);
state[1] = rot + next;
state[2] = w;
return next;
}
// Returns slightly biased random index of a chunk in [0, num_chunks).
HWY_INLINE size_t RandomChunkIndex(const uint32_t num_chunks, uint32_t bits) {
const uint64_t chunk_index = (static_cast<uint64_t>(bits) * num_chunks) >> 32;
HWY_DASSERT(chunk_index < num_chunks);
return static_cast<size_t>(chunk_index);
}
// Writes samples from `keys[0, num)` into `buf`.
template <class D, class Traits, typename T>
HWY_INLINE void DrawSamples(D d, Traits st, T* HWY_RESTRICT keys, size_t num,
T* HWY_RESTRICT buf, uint64_t* HWY_RESTRICT state) {
using V = decltype(Zero(d));
const size_t N = Lanes(d);
// Power of two
constexpr size_t kLanesPerChunk = Constants::LanesPerChunk(sizeof(T));
// Align start of keys to chunks. We have at least 2 chunks (x 64 bytes)
// because the base case handles anything up to 8 vectors (x 16 bytes).
HWY_DASSERT(num >= Constants::SampleLanes<T>());
const size_t misalign =
(reinterpret_cast<uintptr_t>(keys) / sizeof(T)) & (kLanesPerChunk - 1);
if (misalign != 0) {
const size_t consume = kLanesPerChunk - misalign;
keys += consume;
num -= consume;
}
// Generate enough random bits for 6 uint32
uint32_t bits[6];
for (size_t i = 0; i < 6; i += 2) {
const uint64_t bits64 = RandomBits(state);
CopyBytes<8>(&bits64, bits + i);
}
const size_t num_chunks64 = num / kLanesPerChunk;
// Clamp to uint32 for RandomChunkIndex
const uint32_t num_chunks =
static_cast<uint32_t>(HWY_MIN(num_chunks64, 0xFFFFFFFFull));
const size_t offset0 = RandomChunkIndex(num_chunks, bits[0]) * kLanesPerChunk;
const size_t offset1 = RandomChunkIndex(num_chunks, bits[1]) * kLanesPerChunk;
const size_t offset2 = RandomChunkIndex(num_chunks, bits[2]) * kLanesPerChunk;
const size_t offset3 = RandomChunkIndex(num_chunks, bits[3]) * kLanesPerChunk;
const size_t offset4 = RandomChunkIndex(num_chunks, bits[4]) * kLanesPerChunk;
const size_t offset5 = RandomChunkIndex(num_chunks, bits[5]) * kLanesPerChunk;
for (size_t i = 0; i < kLanesPerChunk; i += N) {
const V v0 = Load(d, keys + offset0 + i);
const V v1 = Load(d, keys + offset1 + i);
const V v2 = Load(d, keys + offset2 + i);
const V medians0 = MedianOf3(st, v0, v1, v2);
Store(medians0, d, buf + i);
const V v3 = Load(d, keys + offset3 + i);
const V v4 = Load(d, keys + offset4 + i);
const V v5 = Load(d, keys + offset5 + i);
const V medians1 = MedianOf3(st, v3, v4, v5);
Store(medians1, d, buf + i + kLanesPerChunk);
}
}
template <class V>
V OrXor(const V o, const V x1, const V x2) {
return Or(o, Xor(x1, x2)); // ternlog on AVX3
}
// For detecting inputs where (almost) all keys are equal.
template <class D, class Traits>
HWY_INLINE bool UnsortedSampleEqual(D d, Traits st,
const TFromD<D>* HWY_RESTRICT samples) {
constexpr size_t kSampleLanes = Constants::SampleLanes<TFromD<D>>();
const size_t N = Lanes(d);
// Both are powers of two, so there will be no remainders.
HWY_DASSERT(N < kSampleLanes);
using V = Vec<D>;
const V first = st.SetKey(d, samples);
if (!hwy::IsFloat<TFromD<D>>()) {
// OR of XOR-difference may be faster than comparison.
V diff = Zero(d);
for (size_t i = 0; i < kSampleLanes; i += N) {
const V v = Load(d, samples + i);
diff = OrXor(diff, first, v);
}
return st.NoKeyDifference(d, diff);
} else {
// Disable the OrXor optimization for floats because OrXor will not treat
// subnormals the same as actual comparisons, leading to logic errors for
// 2-value cases.
for (size_t i = 0; i < kSampleLanes; i += N) {
const V v = Load(d, samples + i);
if (!AllTrue(d, st.EqualKeys(d, v, first))) {
return false;
}
}
return true;
}
}
template <class D, class Traits, typename T>
HWY_INLINE void SortSamples(D d, Traits st, T* HWY_RESTRICT buf) {
const size_t N = Lanes(d);
constexpr size_t kSampleLanes = Constants::SampleLanes<T>();
// Network must be large enough to sort two chunks.
HWY_DASSERT(Constants::BaseCaseNumLanes<st.LanesPerKey()>(N) >= kSampleLanes);
BaseCase(d, st, buf, kSampleLanes, buf + kSampleLanes);
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Samples:\n");
for (size_t i = 0; i < kSampleLanes; i += N) {
MaybePrintVector(d, "", Load(d, buf + i), 0, N);
}
}
}
// ------------------------------ Pivot selection
enum class PivotResult {
kDone, // stop without partitioning (all equal, or two-value partition)
kNormal, // partition and recurse left and right
kIsFirst, // partition but skip left recursion
kWasLast, // partition but skip right recursion
};
HWY_INLINE const char* PivotResultString(PivotResult result) {
switch (result) {
case PivotResult::kDone:
return "done";
case PivotResult::kNormal:
return "normal";
case PivotResult::kIsFirst:
return "first";
case PivotResult::kWasLast:
return "last";
}
return "unknown";
}
// (Could vectorize, but only 0.2% of total time)
template <class Traits, typename T>
HWY_INLINE size_t PivotRank(Traits st, const T* HWY_RESTRICT samples) {
constexpr size_t kSampleLanes = Constants::SampleLanes<T>();
constexpr size_t N1 = st.LanesPerKey();
constexpr size_t kRankMid = kSampleLanes / 2;
static_assert(kRankMid % N1 == 0, "Mid is not an aligned key");
// Find the previous value not equal to the median.
size_t rank_prev = kRankMid - N1;
for (; st.Equal1(samples + rank_prev, samples + kRankMid); rank_prev -= N1) {
// All previous samples are equal to the median.
if (rank_prev == 0) return 0;
}
size_t rank_next = rank_prev + N1;
for (; st.Equal1(samples + rank_next, samples + kRankMid); rank_next += N1) {
// The median is also the largest sample. If it is also the largest key,
// we'd end up with an empty right partition, so choose the previous key.
if (rank_next == kSampleLanes - N1) return rank_prev;
}
// If we choose the median as pivot, the ratio of keys ending in the left
// partition will likely be rank_next/kSampleLanes (if the sample is
// representative). This is because equal-to-pivot values also land in the
// left - it's infeasible to do an in-place vectorized 3-way partition.
// Check whether prev would lead to a more balanced partition.
const size_t excess_if_median = rank_next - kRankMid;
const size_t excess_if_prev = kRankMid - rank_prev;
return excess_if_median < excess_if_prev ? kRankMid : rank_prev;
}
// Returns pivot chosen from `samples`. It will never be the largest key
// (thus the right partition will never be empty).
template <class D, class Traits, typename T>
HWY_INLINE Vec<D> ChoosePivotByRank(D d, Traits st,
const T* HWY_RESTRICT samples) {
const size_t pivot_rank = PivotRank(st, samples);
const Vec<D> pivot = st.SetKey(d, samples + pivot_rank);
if (VQSORT_PRINT >= 2) {
fprintf(stderr, " Pivot rank %3zu\n", pivot_rank);
HWY_ALIGN T pivot_lanes[MaxLanes(d)];
Store(pivot, d, pivot_lanes);
using KeyType = typename Traits::KeyType;
KeyType key;
CopyBytes<sizeof(KeyType)>(pivot_lanes, &key);
PrintValue(key);
}
// Verify pivot is not equal to the last sample.
constexpr size_t kSampleLanes = Constants::SampleLanes<T>();
constexpr size_t N1 = st.LanesPerKey();
const Vec<D> last = st.SetKey(d, samples + kSampleLanes - N1);
const bool all_neq = AllTrue(d, st.NotEqualKeys(d, pivot, last));
(void)all_neq;
HWY_DASSERT(all_neq);
return pivot;
}
// Returns true if all keys equal `pivot`, otherwise returns false and sets
// `*first_mismatch' to the index of the first differing key.
template <class D, class Traits, typename T>
HWY_INLINE bool AllEqual(D d, Traits st, const Vec<D> pivot,
const T* HWY_RESTRICT keys, size_t num,
size_t* HWY_RESTRICT first_mismatch) {
const size_t N = Lanes(d);
// Ensures we can use overlapping loads for the tail; see HandleSpecialCases.
HWY_DASSERT(num >= N);
const Vec<D> zero = Zero(d);
// Vector-align keys + i.
const size_t misalign =
(reinterpret_cast<uintptr_t>(keys) / sizeof(T)) & (N - 1);
HWY_DASSERT(misalign % st.LanesPerKey() == 0);
const size_t consume = N - misalign;
{
const Vec<D> v = LoadU(d, keys);
// Only check masked lanes; consider others to be equal.
const Mask<D> diff = And(FirstN(d, consume), st.NotEqualKeys(d, v, pivot));
if (HWY_UNLIKELY(!AllFalse(d, diff))) {
const size_t lane = FindKnownFirstTrue(d, diff);
*first_mismatch = lane;
return false;
}
}
size_t i = consume;
HWY_DASSERT(((reinterpret_cast<uintptr_t>(keys + i) / sizeof(T)) & (N - 1)) ==
0);
// Disable the OrXor optimization for floats because OrXor will not treat
// subnormals the same as actual comparisons, leading to logic errors for
// 2-value cases.
if (!hwy::IsFloat<T>()) {
// Sticky bits registering any difference between `keys` and the first key.
// We use vector XOR because it may be cheaper than comparisons, especially
// for 128-bit. 2x unrolled for more ILP.
Vec<D> diff0 = zero;
Vec<D> diff1 = zero;
// We want to stop once a difference has been found, but without slowing
// down the loop by comparing during each iteration. The compromise is to
// compare after a 'group', which consists of kLoops times two vectors.
constexpr size_t kLoops = 8;
const size_t lanes_per_group = kLoops * 2 * N;
if (num >= lanes_per_group) {
for (; i <= num - lanes_per_group; i += lanes_per_group) {
HWY_DEFAULT_UNROLL
for (size_t loop = 0; loop < kLoops; ++loop) {
const Vec<D> v0 = Load(d, keys + i + loop * 2 * N);
const Vec<D> v1 = Load(d, keys + i + loop * 2 * N + N);
diff0 = OrXor(diff0, v0, pivot);
diff1 = OrXor(diff1, v1, pivot);
}
// If there was a difference in the entire group:
if (HWY_UNLIKELY(!st.NoKeyDifference(d, Or(diff0, diff1)))) {
// .. then loop until the first one, with termination guarantee.
for (;; i += N) {
const Vec<D> v = Load(d, keys + i);
const Mask<D> diff = st.NotEqualKeys(d, v, pivot);
if (HWY_UNLIKELY(!AllFalse(d, diff))) {
const size_t lane = FindKnownFirstTrue(d, diff);
*first_mismatch = i + lane;
return false;
}
}
}
}
}
} // !hwy::IsFloat<T>()
// Whole vectors, no unrolling, compare directly
for (; i <= num - N; i += N) {
const Vec<D> v = Load(d, keys + i);
const Mask<D> diff = st.NotEqualKeys(d, v, pivot);
if (HWY_UNLIKELY(!AllFalse(d, diff))) {
const size_t lane = FindKnownFirstTrue(d, diff);
*first_mismatch = i + lane;
return false;
}
}
// Always re-check the last (unaligned) vector to reduce branching.
i = num - N;
const Vec<D> v = LoadU(d, keys + i);
const Mask<D> diff = st.NotEqualKeys(d, v, pivot);
if (HWY_UNLIKELY(!AllFalse(d, diff))) {
const size_t lane = FindKnownFirstTrue(d, diff);
*first_mismatch = i + lane;
return false;
}
if (VQSORT_PRINT >= 1) {
fprintf(stderr, "All keys equal\n");
}
return true; // all equal
}
// Called from 'two locations', but only one is active (IsKV is constexpr).
template <class D, class Traits, typename T>
HWY_INLINE bool ExistsAnyBefore(D d, Traits st, const T* HWY_RESTRICT keys,
size_t num, const Vec<D> pivot) {
const size_t N = Lanes(d);
HWY_DASSERT(num >= N); // See HandleSpecialCases
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Scanning for before\n");
}
size_t i = 0;
constexpr size_t kLoops = 16;
const size_t lanes_per_group = kLoops * N;
Vec<D> first = pivot;
// Whole group, unrolled
if (num >= lanes_per_group) {
for (; i <= num - lanes_per_group; i += lanes_per_group) {
HWY_DEFAULT_UNROLL
for (size_t loop = 0; loop < kLoops; ++loop) {
const Vec<D> curr = LoadU(d, keys + i + loop * N);
first = st.First(d, first, curr);
}
if (HWY_UNLIKELY(!AllFalse(d, st.Compare(d, first, pivot)))) {
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Stopped scanning at end of group %zu\n",
i + lanes_per_group);
}
return true;
}
}
}
// Whole vectors, no unrolling
for (; i <= num - N; i += N) {
const Vec<D> curr = LoadU(d, keys + i);
if (HWY_UNLIKELY(!AllFalse(d, st.Compare(d, curr, pivot)))) {
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Stopped scanning at %zu\n", i);
}
return true;
}
}
// If there are remainders, re-check the last whole vector.
if (HWY_LIKELY(i != num)) {
const Vec<D> curr = LoadU(d, keys + num - N);
if (HWY_UNLIKELY(!AllFalse(d, st.Compare(d, curr, pivot)))) {
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Stopped scanning at last %zu\n", num - N);
}
return true;
}
}
return false; // pivot is the first
}
// Called from 'two locations', but only one is active (IsKV is constexpr).
template <class D, class Traits, typename T>
HWY_INLINE bool ExistsAnyAfter(D d, Traits st, const T* HWY_RESTRICT keys,
size_t num, const Vec<D> pivot) {
const size_t N = Lanes(d);
HWY_DASSERT(num >= N); // See HandleSpecialCases
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Scanning for after\n");
}
size_t i = 0;
constexpr size_t kLoops = 16;
const size_t lanes_per_group = kLoops * N;
Vec<D> last = pivot;
// Whole group, unrolled
if (num >= lanes_per_group) {
for (; i + lanes_per_group <= num; i += lanes_per_group) {
HWY_DEFAULT_UNROLL
for (size_t loop = 0; loop < kLoops; ++loop) {
const Vec<D> curr = LoadU(d, keys + i + loop * N);
last = st.Last(d, last, curr);
}
if (HWY_UNLIKELY(!AllFalse(d, st.Compare(d, pivot, last)))) {
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Stopped scanning at end of group %zu\n",
i + lanes_per_group);
}
return true;
}
}
}
// Whole vectors, no unrolling
for (; i <= num - N; i += N) {
const Vec<D> curr = LoadU(d, keys + i);
if (HWY_UNLIKELY(!AllFalse(d, st.Compare(d, pivot, curr)))) {
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Stopped scanning at %zu\n", i);
}
return true;
}
}
// If there are remainders, re-check the last whole vector.
if (HWY_LIKELY(i != num)) {
const Vec<D> curr = LoadU(d, keys + num - N);
if (HWY_UNLIKELY(!AllFalse(d, st.Compare(d, pivot, curr)))) {
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Stopped scanning at last %zu\n", num - N);
}
return true;
}
}
return false; // pivot is the last
}
// Returns pivot chosen from `keys[0, num)`. It will never be the largest key
// (thus the right partition will never be empty).
template <class D, class Traits, typename T>
HWY_INLINE Vec<D> ChoosePivotForEqualSamples(D d, Traits st,
T* HWY_RESTRICT keys, size_t num,
T* HWY_RESTRICT samples,
Vec<D> second, Vec<D> third,
PivotResult& result) {
const Vec<D> pivot = st.SetKey(d, samples); // the single unique sample
// Early out for mostly-0 arrays, where pivot is often FirstValue.
if (HWY_UNLIKELY(AllTrue(d, st.EqualKeys(d, pivot, st.FirstValue(d))))) {
result = PivotResult::kIsFirst;
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Pivot equals first possible value\n");
}
return pivot;
}
if (HWY_UNLIKELY(AllTrue(d, st.EqualKeys(d, pivot, st.LastValue(d))))) {
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "Pivot equals last possible value\n");
}
result = PivotResult::kWasLast;
return st.PrevValue(d, pivot);
}
// If key-value, we didn't run PartitionIfTwo* and thus `third` is unknown and
// cannot be used.
if (st.IsKV()) {
// If true, pivot is either middle or last.
const bool before = !AllFalse(d, st.Compare(d, second, pivot));
if (HWY_UNLIKELY(before)) {
// Not last, so middle.
if (HWY_UNLIKELY(ExistsAnyAfter(d, st, keys, num, pivot))) {
result = PivotResult::kNormal;
return pivot;
}
// We didn't find anything after pivot, so it is the last. Because keys
// equal to the pivot go to the left partition, the right partition would
// be empty and Partition will not have changed anything. Instead use the
// previous value in sort order, which is not necessarily an actual key.
result = PivotResult::kWasLast;
return st.PrevValue(d, pivot);
}
// Otherwise, pivot is first or middle. Rule out it being first:
if (HWY_UNLIKELY(ExistsAnyBefore(d, st, keys, num, pivot))) {
result = PivotResult::kNormal;
return pivot;
}
// It is first: fall through to shared code below.
} else {
// Check if pivot is between two known values. If so, it is not the first
// nor the last and we can avoid scanning.
st.Sort2(d, second, third);
HWY_DASSERT(AllTrue(d, st.Compare(d, second, third)));
const bool before = !AllFalse(d, st.Compare(d, second, pivot));
const bool after = !AllFalse(d, st.Compare(d, pivot, third));
// Only reached if there are three keys, which means pivot is either first,
// last, or in between. Thus there is another key that comes before or
// after.
HWY_DASSERT(before || after);
if (HWY_UNLIKELY(before)) {
// Neither first nor last.
if (HWY_UNLIKELY(after || ExistsAnyAfter(d, st, keys, num, pivot))) {
result = PivotResult::kNormal;
return pivot;
}
// We didn't find anything after pivot, so it is the last. Because keys
// equal to the pivot go to the left partition, the right partition would
// be empty and Partition will not have changed anything. Instead use the
// previous value in sort order, which is not necessarily an actual key.
result = PivotResult::kWasLast;
return st.PrevValue(d, pivot);
}
// Has after, and we found one before: in the middle.
if (HWY_UNLIKELY(ExistsAnyBefore(d, st, keys, num, pivot))) {
result = PivotResult::kNormal;
return pivot;
}
}
// Pivot is first. We could consider a special partition mode that only
// reads from and writes to the right side, and later fills in the left
// side, which we know is equal to the pivot. However, that leads to more
// cache misses if the array is large, and doesn't save much, hence is a
// net loss.
result = PivotResult::kIsFirst;
return pivot;
}
// ------------------------------ Quicksort recursion
template <class D, class Traits, typename T>
HWY_NOINLINE void PrintMinMax(D d, Traits st, const T* HWY_RESTRICT keys,
size_t num, T* HWY_RESTRICT buf) {
if (VQSORT_PRINT >= 2) {
const size_t N = Lanes(d);
if (num < N) return;
Vec<D> first = st.LastValue(d);
Vec<D> last = st.FirstValue(d);
size_t i = 0;
for (; i <= num - N; i += N) {
const Vec<D> v = LoadU(d, keys + i);
first = st.First(d, v, first);
last = st.Last(d, v, last);
}
if (HWY_LIKELY(i != num)) {
HWY_DASSERT(num >= N); // See HandleSpecialCases
const Vec<D> v = LoadU(d, keys + num - N);
first = st.First(d, v, first);
last = st.Last(d, v, last);
}
first = st.FirstOfLanes(d, first, buf);
last = st.LastOfLanes(d, last, buf);
MaybePrintVector(d, "first", first, 0, st.LanesPerKey());
MaybePrintVector(d, "last", last, 0, st.LanesPerKey());
}
}
template <class D, class Traits, typename T>
HWY_NOINLINE void Recurse(D d, Traits st, T* HWY_RESTRICT keys,
const size_t num, T* HWY_RESTRICT buf,
uint64_t* HWY_RESTRICT state,
const size_t remaining_levels) {
HWY_DASSERT(num != 0);
const size_t N = Lanes(d);
constexpr size_t kLPK = st.LanesPerKey();
if (HWY_UNLIKELY(num <= Constants::BaseCaseNumLanes<kLPK>(N))) {
BaseCase(d, st, keys, num, buf);
return;
}
// Move after BaseCase so we skip printing for small subarrays.
if (VQSORT_PRINT >= 1) {
fprintf(stderr, "\n\n=== Recurse depth=%zu len=%zu\n", remaining_levels,
num);
PrintMinMax(d, st, keys, num, buf);
}
DrawSamples(d, st, keys, num, buf, state);
Vec<D> pivot;
PivotResult result = PivotResult::kNormal;
if (HWY_UNLIKELY(UnsortedSampleEqual(d, st, buf))) {
pivot = st.SetKey(d, buf);
size_t idx_second = 0;
if (HWY_UNLIKELY(AllEqual(d, st, pivot, keys, num, &idx_second))) {
return;
}
HWY_DASSERT(idx_second % st.LanesPerKey() == 0);
// Must capture the value before PartitionIfTwoKeys may overwrite it.
const Vec<D> second = st.SetKey(d, keys + idx_second);
MaybePrintVector(d, "pivot", pivot, 0, st.LanesPerKey());
MaybePrintVector(d, "second", second, 0, st.LanesPerKey());
Vec<D> third;
// Not supported for key-value types because two 'keys' may be equivalent
// but not interchangeable (their values may differ).
if (HWY_UNLIKELY(!st.IsKV() &&
PartitionIfTwoKeys(d, st, pivot, keys, num, idx_second,
second, third, buf))) {
return; // Done, skip recursion because each side has all-equal keys.
}
// We can no longer start scanning from idx_second because
// PartitionIfTwoKeys may have reordered keys.
pivot = ChoosePivotForEqualSamples(d, st, keys, num, buf, second, third,
result);
// If kNormal, `pivot` is very common but not the first/last. It is
// tempting to do a 3-way partition (to avoid moving the =pivot keys a
// second time), but that is a net loss due to the extra comparisons.
} else {
SortSamples(d, st, buf);
// Not supported for key-value types because two 'keys' may be equivalent
// but not interchangeable (their values may differ).
if (HWY_UNLIKELY(!st.IsKV() &&
PartitionIfTwoSamples(d, st, keys, num, buf))) {
return;
}
pivot = ChoosePivotByRank(d, st, buf);
}
// Too many recursions. This is unlikely to happen because we select pivots
// from large (though still O(1)) samples.
if (HWY_UNLIKELY(remaining_levels == 0)) {
if (VQSORT_PRINT >= 1) {
fprintf(stderr, "HeapSort reached, size=%zu\n", num);
}
HeapSort(st, keys, num); // Slow but N*logN.
return;
}
const size_t bound = Partition(d, st, keys, num, pivot, buf);
if (VQSORT_PRINT >= 2) {
fprintf(stderr, "bound %zu num %zu result %s\n", bound, num,
PivotResultString(result));
}
// The left partition is not empty because the pivot is usually one of the
// keys. Exception: if kWasLast, we set pivot to PrevValue(pivot), but we
// still have at least one value <= pivot because AllEqual ruled out the case
// of only one unique value. Note that for floating-point, PrevValue can
// return the same value (for -inf inputs), but that would just mean the
// pivot is again one of the keys.
HWY_DASSERT(bound != 0);
// ChoosePivot* ensure pivot != last, so the right partition is never empty
// except in the rare case of the pivot matching the last-in-sort-order value,
// which implies we anyway skip the right partition due to kWasLast.
HWY_DASSERT(bound != num || result == PivotResult::kWasLast);
if (HWY_LIKELY(result != PivotResult::kIsFirst)) {
Recurse(d, st, keys, bound, buf, state, remaining_levels - 1);
}
if (HWY_LIKELY(result != PivotResult::kWasLast)) {
Recurse(d, st, keys + bound, num - bound, buf, state, remaining_levels - 1);
}
}
// Returns true if sorting is finished.
template <class D, class Traits, typename T>
HWY_INLINE bool HandleSpecialCases(D d, Traits st, T* HWY_RESTRICT keys,
size_t num, T* HWY_RESTRICT buf) {
const size_t N = Lanes(d);
constexpr size_t kLPK = st.LanesPerKey();
const size_t base_case_num = Constants::BaseCaseNumLanes<kLPK>(N);
// Recurse will also check this, but doing so here first avoids setting up
// the random generator state.
if (HWY_UNLIKELY(num <= base_case_num)) {
if (VQSORT_PRINT >= 1) {
fprintf(stderr, "Special-casing small, %d lanes\n",
static_cast<int>(num));
}
BaseCase(d, st, keys, num, buf);
return true;
}
// 128-bit keys require vectors with at least two u64 lanes, which is always
// the case unless `d` requests partial vectors (e.g. fraction = 1/2) AND the
// hardware vector width is less than 128bit / fraction.
const bool partial_128 = !IsFull(d) && N < 2 && st.Is128();
// Partition assumes its input is at least two vectors. If vectors are huge,
// base_case_num may actually be smaller. If so, which is only possible on
// RVV, pass a capped or partial d (LMUL < 1). Use HWY_MAX_BYTES instead of
// HWY_LANES to account for the largest possible LMUL.
constexpr bool kPotentiallyHuge =
HWY_MAX_BYTES / sizeof(T) > Constants::kMaxRows * Constants::kMaxCols;
const bool huge_vec = kPotentiallyHuge && (2 * N > base_case_num);
if (partial_128 || huge_vec) {
if (VQSORT_PRINT >= 1) {
fprintf(stderr, "WARNING: using slow HeapSort: partial %d huge %d\n",
partial_128, huge_vec);
}
HeapSort(st, keys, num);
return true;
}
// We could also check for already sorted/reverse/equal, but that's probably
// counterproductive if vqsort is used as a base case.
return false; // not finished sorting
}
#endif // VQSORT_ENABLED
template <class D, class Traits, typename T, HWY_IF_FLOAT(T)>
HWY_INLINE size_t CountAndReplaceNaN(D d, Traits st, T* HWY_RESTRICT keys,
size_t num) {
const size_t N = Lanes(d);
// Will be sorted to the back of the array.
const Vec<D> sentinel = st.LastValue(d);
size_t num_nan = 0;
size_t i = 0;
if (num >= N) {
for (; i <= num - N; i += N) {
const Mask<D> is_nan = IsNaN(LoadU(d, keys + i));
BlendedStore(sentinel, is_nan, d, keys + i);
num_nan += CountTrue(d, is_nan);
}
}
const size_t remaining = num - i;
HWY_DASSERT(remaining < N);
const Vec<D> v = LoadN(d, keys + i, remaining);
const Mask<D> is_nan = IsNaN(v);
StoreN(IfThenElse(is_nan, sentinel, v), d, keys + i, remaining);
num_nan += CountTrue(d, is_nan);
return num_nan;
}
// IsNaN is not implemented for non-float, so skip it.
template <class D, class Traits, typename T, HWY_IF_NOT_FLOAT(T)>
HWY_INLINE size_t CountAndReplaceNaN(D, Traits, T* HWY_RESTRICT, size_t) {
return 0;
}
} // namespace detail
// Old interface with user-specified buffer, retained for compatibility. Called
// by the newer overload below. `buf` must be vector-aligned and hold at least
// SortConstants::BufBytes(HWY_MAX_BYTES, st.LanesPerKey()).
template <class D, class Traits, typename T>
void Sort(D d, Traits st, T* HWY_RESTRICT keys, size_t num,
T* HWY_RESTRICT buf) {
if (VQSORT_PRINT >= 1) {
fprintf(stderr,
"=============== Sort num %zu is128 %d isKV %d vec bytes %d\n", num,
st.Is128(), st.IsKV(), static_cast<int>(sizeof(T) * Lanes(d)));
}
#if HWY_MAX_BYTES > 64
// sorting_networks-inl and traits assume no more than 512 bit vectors.
if (HWY_UNLIKELY(Lanes(d) > 64 / sizeof(T))) {
return Sort(CappedTag<T, 64 / sizeof(T)>(), st, keys, num, buf);
}
#endif // HWY_MAX_BYTES > 64
const size_t num_nan = detail::CountAndReplaceNaN(d, st, keys, num);
#if VQSORT_ENABLED || HWY_IDE
if (!detail::HandleSpecialCases(d, st, keys, num, buf)) {
uint64_t* HWY_RESTRICT state = hwy::detail::GetGeneratorStateStatic();
// Introspection: switch to worst-case N*logN heapsort after this many.
// Should never be reached, so computing log2 exactly does not help.
const size_t max_levels = 50;
detail::Recurse(d, st, keys, num, buf, state, max_levels);
}
#else // !VQSORT_ENABLED
(void)d;
(void)buf;
if (VQSORT_PRINT >= 1) {
fprintf(stderr, "WARNING: using slow HeapSort because vqsort disabled\n");
}
detail::HeapSort(st, keys, num);
#endif // VQSORT_ENABLED
if (num_nan != 0) {
Fill(d, GetLane(NaN(d)), num_nan, keys + num - num_nan);
}
}
// Sorts `keys[0..num-1]` according to the order defined by `st.Compare`.
// In-place i.e. O(1) additional storage. Worst-case N*logN comparisons.
// Non-stable (order of equal keys may change), except for the common case where
// the upper bits of T are the key, and the lower bits are a sequential or at
// least unique ID. Any NaN will be moved to the back of the array and replaced
// with the canonical NaN(d).
// There is no upper limit on `num`, but note that pivots may be chosen by
// sampling only from the first 256 GiB.
//
// `d` is typically SortTag<T> (chooses between full and partial vectors).
// `st` is SharedTraits<Traits*<Order*>>. This abstraction layer bridges
// differences in sort order and single-lane vs 128-bit keys.
template <class D, class Traits, typename T>
HWY_API void Sort(D d, Traits st, T* HWY_RESTRICT keys, size_t num) {
constexpr size_t kLPK = st.LanesPerKey();
HWY_ALIGN T buf[SortConstants::BufBytes<T, kLPK>(HWY_MAX_BYTES) / sizeof(T)];
return Sort(d, st, keys, num, buf);
}
#if VQSORT_ENABLED
// Adapter from VQSort[Static] to SortTag and Traits*/Order*.
namespace detail {
// Primary template for built-in key types
template <typename T>
struct KeyAdapter {
using Ascending = OrderAscending<T>;
using Descending = OrderDescending<T>;
template <class Order>
using Traits = TraitsLane<Order>;
};
template <>
struct KeyAdapter<hwy::uint128_t> {
using Ascending = OrderAscending128;
using Descending = OrderDescending128;
template <class Order>
using Traits = Traits128<Order>;
};
template <>
struct KeyAdapter<hwy::K64V64> {
using Ascending = OrderAscendingKV128;
using Descending = OrderDescendingKV128;
template <class Order>
using Traits = Traits128<Order>;
};
template <>
struct KeyAdapter<hwy::K32V32> {
using Ascending = OrderAscendingKV64;
using Descending = OrderDescendingKV64;
template <class Order>
using Traits = TraitsLane<Order>;
};
} // namespace detail
#endif // VQSORT_ENABLED
// Simpler interface matching VQSort(), but without dynamic dispatch. Uses the
// instructions available in the current target (HWY_NAMESPACE). Supported key
// types: 16-64 bit unsigned/signed/floating-point (but float64 only #if
// HWY_HAVE_FLOAT64), uint128_t, K64V64, K32V32.
template <typename T>
void VQSortStatic(T* HWY_RESTRICT keys, size_t num, SortAscending) {
#if VQSORT_ENABLED
using Adapter = detail::KeyAdapter<T>;
using Order = typename Adapter::Ascending;
const detail::SharedTraits<typename Adapter::template Traits<Order>> st;
using LaneType = typename decltype(st)::LaneType;
const SortTag<LaneType> d;
Sort(d, st, reinterpret_cast<LaneType*>(keys), num * st.LanesPerKey());
#else
(void)keys;
(void)num;
HWY_ASSERT(0);
#endif // VQSORT_ENABLED
}
template <typename T>
void VQSortStatic(T* HWY_RESTRICT keys, size_t num, SortDescending) {
#if VQSORT_ENABLED
using Adapter = detail::KeyAdapter<T>;
using Order = typename Adapter::Descending;
const detail::SharedTraits<typename Adapter::template Traits<Order>> st;
using LaneType = typename decltype(st)::LaneType;
const SortTag<LaneType> d;
Sort(d, st, reinterpret_cast<LaneType*>(keys), num * st.LanesPerKey());
#else
(void)keys;
(void)num;
HWY_ASSERT(0);
#endif // VQSORT_ENABLED
}
// NOLINTNEXTLINE(google-readability-namespace-comments)
} // namespace HWY_NAMESPACE
} // namespace hwy
HWY_AFTER_NAMESPACE();
#endif // HIGHWAY_HWY_CONTRIB_SORT_VQSORT_TOGGLE