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/*
* Copyright 2006 The Android Open Source Project
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkUtils_DEFINED
#define SkUtils_DEFINED
#include "include/private/base/SkAttributes.h"
#include <cstring>
#include <type_traits> // is_trivially_copyable
namespace SkHexadecimalDigits {
extern const char gUpper[16]; // 0-9A-F
extern const char gLower[16]; // 0-9a-f
} // namespace SkHexadecimalDigits
///////////////////////////////////////////////////////////////////////////////
// If T is an 8-byte GCC or Clang vector extension type, it would naturally pass or return in the
// MMX mm0 register on 32-bit x86 builds. This has the fun side effect of clobbering any state in
// the x87 st0 register. (There is no ABI governing who should preserve mm?/st? registers, so no
// one does!)
//
// We force-inline sk_unaligned_load() and sk_unaligned_store() to avoid that, making them safe to
// use for all types on all platforms, thus solving the problem once and for all!
// A separate problem exists with 32-bit x86. The default calling convention returns values in
// ST0 (the x87 FPU). Unfortunately, doing so can mutate some bit patterns (signaling NaNs
// become quiet). If you're using these functions to pass data around as floats, but it's actually
// integers, that can be bad -- raster pipeline does this.
//
// With GCC and Clang, the always_inline attribute ensures we don't have a problem. MSVC, though,
// ignores __forceinline in debug builds, so the return-via-ST0 is always present. Switching to
// __vectorcall changes the functions to return in xmm0.
#if defined(_MSC_VER) && defined(_M_IX86)
#define SK_FP_SAFE_ABI __vectorcall
#else
#define SK_FP_SAFE_ABI
#endif
template <typename T, typename P>
static SK_ALWAYS_INLINE T SK_FP_SAFE_ABI sk_unaligned_load(const P* ptr) {
static_assert(std::is_trivially_copyable_v<P> || std::is_void_v<P>);
static_assert(std::is_trivially_copyable_v<T>);
T val;
// gcc's class-memaccess sometimes triggers when:
// - `T` is trivially copyable but
// - `T` is non-trivial (e.g. at least one eligible default constructor is
// non-trivial).
// Use `reinterpret_cast<const void*>` to explicit suppress this warning; a
// trivially copyable type is safe to memcpy from/to.
memcpy(&val, static_cast<const void*>(ptr), sizeof(val));
return val;
}
template <typename T, typename P>
static SK_ALWAYS_INLINE void SK_FP_SAFE_ABI sk_unaligned_store(P* ptr, T val) {
static_assert(std::is_trivially_copyable<T>::value);
memcpy(ptr, &val, sizeof(val));
}
// Copy the bytes from src into an instance of type Dst and return it.
template <typename Dst, typename Src>
static SK_ALWAYS_INLINE Dst SK_FP_SAFE_ABI sk_bit_cast(const Src& src) {
static_assert(sizeof(Dst) == sizeof(Src));
static_assert(std::is_trivially_copyable<Dst>::value);
static_assert(std::is_trivially_copyable<Src>::value);
return sk_unaligned_load<Dst>(&src);
}
#undef SK_FP_SAFE_ABI
#endif