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// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#include "lib/jxl/dec_huffman.h"
#include <jxl/types.h>
#include <string.h> /* for memset */
#include <vector>
#include "lib/jxl/ans_params.h"
#include "lib/jxl/base/bits.h"
#include "lib/jxl/huffman_table.h"
namespace jxl {
static const int kCodeLengthCodes = 18;
static const uint8_t kCodeLengthCodeOrder[kCodeLengthCodes] = {
1, 2, 3, 4, 0, 5, 17, 6, 16, 7, 8, 9, 10, 11, 12, 13, 14, 15,
};
static const uint8_t kDefaultCodeLength = 8;
static const uint8_t kCodeLengthRepeatCode = 16;
JXL_BOOL ReadHuffmanCodeLengths(const uint8_t* code_length_code_lengths,
int num_symbols, uint8_t* code_lengths,
BitReader* br) {
int symbol = 0;
uint8_t prev_code_len = kDefaultCodeLength;
int repeat = 0;
uint8_t repeat_code_len = 0;
int space = 32768;
HuffmanCode table[32];
uint16_t counts[16] = {0};
for (int i = 0; i < kCodeLengthCodes; ++i) {
++counts[code_length_code_lengths[i]];
}
if (!BuildHuffmanTable(table, 5, code_length_code_lengths, kCodeLengthCodes,
&counts[0])) {
return JXL_FALSE;
}
while (symbol < num_symbols && space > 0) {
const HuffmanCode* p = table;
uint8_t code_len;
br->Refill();
p += br->PeekFixedBits<5>();
br->Consume(p->bits);
code_len = static_cast<uint8_t>(p->value);
if (code_len < kCodeLengthRepeatCode) {
repeat = 0;
code_lengths[symbol++] = code_len;
if (code_len != 0) {
prev_code_len = code_len;
space -= 32768u >> code_len;
}
} else {
const int extra_bits = code_len - 14;
int old_repeat;
int repeat_delta;
uint8_t new_len = 0;
if (code_len == kCodeLengthRepeatCode) {
new_len = prev_code_len;
}
if (repeat_code_len != new_len) {
repeat = 0;
repeat_code_len = new_len;
}
old_repeat = repeat;
if (repeat > 0) {
repeat -= 2;
repeat <<= extra_bits;
}
repeat += static_cast<int>(br->ReadBits(extra_bits) + 3);
repeat_delta = repeat - old_repeat;
if (symbol + repeat_delta > num_symbols) {
return 0;
}
memset(&code_lengths[symbol], repeat_code_len,
static_cast<size_t>(repeat_delta));
symbol += repeat_delta;
if (repeat_code_len != 0) {
space -= repeat_delta << (15 - repeat_code_len);
}
}
}
if (space != 0) {
return JXL_FALSE;
}
memset(&code_lengths[symbol], 0, static_cast<size_t>(num_symbols - symbol));
return JXL_TRUE;
}
static JXL_INLINE bool ReadSimpleCode(size_t alphabet_size, BitReader* br,
HuffmanCode* table) {
size_t max_bits =
(alphabet_size > 1u) ? FloorLog2Nonzero(alphabet_size - 1u) + 1 : 0;
size_t num_symbols = br->ReadFixedBits<2>() + 1;
uint16_t symbols[4] = {0};
for (size_t i = 0; i < num_symbols; ++i) {
uint16_t symbol = br->ReadBits(max_bits);
if (symbol >= alphabet_size) {
return false;
}
symbols[i] = symbol;
}
for (size_t i = 0; i < num_symbols - 1; ++i) {
for (size_t j = i + 1; j < num_symbols; ++j) {
if (symbols[i] == symbols[j]) return false;
}
}
// 4 symbols have to option to encode.
if (num_symbols == 4) num_symbols += br->ReadFixedBits<1>();
const auto swap_symbols = [&symbols](size_t i, size_t j) {
uint16_t t = symbols[j];
symbols[j] = symbols[i];
symbols[i] = t;
};
size_t table_size = 1;
switch (num_symbols) {
case 1:
table[0] = {0, symbols[0]};
break;
case 2:
if (symbols[0] > symbols[1]) swap_symbols(0, 1);
table[0] = {1, symbols[0]};
table[1] = {1, symbols[1]};
table_size = 2;
break;
case 3:
if (symbols[1] > symbols[2]) swap_symbols(1, 2);
table[0] = {1, symbols[0]};
table[2] = {1, symbols[0]};
table[1] = {2, symbols[1]};
table[3] = {2, symbols[2]};
table_size = 4;
break;
case 4: {
for (size_t i = 0; i < 3; ++i) {
for (size_t j = i + 1; j < 4; ++j) {
if (symbols[i] > symbols[j]) swap_symbols(i, j);
}
}
table[0] = {2, symbols[0]};
table[2] = {2, symbols[1]};
table[1] = {2, symbols[2]};
table[3] = {2, symbols[3]};
table_size = 4;
break;
}
case 5: {
if (symbols[2] > symbols[3]) swap_symbols(2, 3);
table[0] = {1, symbols[0]};
table[1] = {2, symbols[1]};
table[2] = {1, symbols[0]};
table[3] = {3, symbols[2]};
table[4] = {1, symbols[0]};
table[5] = {2, symbols[1]};
table[6] = {1, symbols[0]};
table[7] = {3, symbols[3]};
table_size = 8;
break;
}
default: {
// Unreachable.
return false;
}
}
const uint32_t goal_size = 1u << kHuffmanTableBits;
while (table_size != goal_size) {
memcpy(&table[table_size], &table[0],
static_cast<size_t>(table_size) * sizeof(table[0]));
table_size <<= 1;
}
return true;
}
bool HuffmanDecodingData::ReadFromBitStream(size_t alphabet_size,
BitReader* br) {
if (alphabet_size > (1 << PREFIX_MAX_BITS)) return false;
/* simple_code_or_skip is used as follows:
1 for simple code;
0 for no skipping, 2 skips 2 code lengths, 3 skips 3 code lengths */
uint32_t simple_code_or_skip = br->ReadFixedBits<2>();
if (simple_code_or_skip == 1u) {
table_.resize(1u << kHuffmanTableBits);
return ReadSimpleCode(alphabet_size, br, table_.data());
}
std::vector<uint8_t> code_lengths(alphabet_size, 0);
uint8_t code_length_code_lengths[kCodeLengthCodes] = {0};
int space = 32;
int num_codes = 0;
/* Static Huffman code for the code length code lengths */
static const HuffmanCode huff[16] = {
{2, 0}, {2, 4}, {2, 3}, {3, 2}, {2, 0}, {2, 4}, {2, 3}, {4, 1},
{2, 0}, {2, 4}, {2, 3}, {3, 2}, {2, 0}, {2, 4}, {2, 3}, {4, 5},
};
for (size_t i = simple_code_or_skip; i < kCodeLengthCodes && space > 0; ++i) {
const int code_len_idx = kCodeLengthCodeOrder[i];
const HuffmanCode* p = huff;
uint8_t v;
br->Refill();
p += br->PeekFixedBits<4>();
br->Consume(p->bits);
v = static_cast<uint8_t>(p->value);
code_length_code_lengths[code_len_idx] = v;
if (v != 0) {
space -= (32u >> v);
++num_codes;
}
}
bool ok =
(num_codes == 1 || space == 0) &&
FROM_JXL_BOOL(ReadHuffmanCodeLengths(
code_length_code_lengths, alphabet_size, code_lengths.data(), br));
if (!ok) return false;
uint16_t counts[16] = {0};
for (size_t i = 0; i < alphabet_size; ++i) {
++counts[code_lengths[i]];
}
table_.resize(alphabet_size + 376);
uint32_t table_size =
BuildHuffmanTable(table_.data(), kHuffmanTableBits, code_lengths.data(),
alphabet_size, &counts[0]);
table_.resize(table_size);
return (table_size > 0);
}
// Decodes the next Huffman coded symbol from the bit-stream.
uint16_t HuffmanDecodingData::ReadSymbol(BitReader* br) const {
size_t n_bits;
const HuffmanCode* table = table_.data();
table += br->PeekBits(kHuffmanTableBits);
n_bits = table->bits;
if (n_bits > kHuffmanTableBits) {
br->Consume(kHuffmanTableBits);
n_bits -= kHuffmanTableBits;
table += table->value;
table += br->PeekBits(n_bits);
}
br->Consume(table->bits);
return table->value;
}
} // namespace jxl