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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/jpeg/enc_jpeg_huffman_decode.h"
#include "lib/jxl/jpeg/jpeg_data.h"
namespace jxl {
namespace jpeg {
// Returns the table width of the next 2nd level table, count is the histogram
// of bit lengths for the remaining symbols, len is the code length of the next
// processed symbol.
static inline int NextTableBitSize(const int* count, int len) {
int left = 1 << (len - kJpegHuffmanRootTableBits);
while (len < static_cast<int>(kJpegHuffmanMaxBitLength)) {
left -= count[len];
if (left <= 0) break;
++len;
left <<= 1;
}
return len - kJpegHuffmanRootTableBits;
}
void BuildJpegHuffmanTable(const uint32_t* count, const uint32_t* symbols,
HuffmanTableEntry* lut) {
HuffmanTableEntry code; // current table entry
HuffmanTableEntry* table; // next available space in table
int len; // current code length
int idx; // symbol index
int key; // prefix code
int reps; // number of replicate key values in current table
int low; // low bits for current root entry
int table_bits; // key length of current table
int table_size; // size of current table
// Make a local copy of the input bit length histogram.
int tmp_count[kJpegHuffmanMaxBitLength + 1] = {0};
int total_count = 0;
for (len = 1; len <= static_cast<int>(kJpegHuffmanMaxBitLength); ++len) {
tmp_count[len] = count[len];
total_count += tmp_count[len];
}
table = lut;
table_bits = kJpegHuffmanRootTableBits;
table_size = 1 << table_bits;
// Special case code with only one value.
if (total_count == 1) {
code.bits = 0;
code.value = symbols[0];
for (key = 0; key < table_size; ++key) {
table[key] = code;
}
return;
}
// Fill in root table.
key = 0;
idx = 0;
for (len = 1; len <= kJpegHuffmanRootTableBits; ++len) {
for (; tmp_count[len] > 0; --tmp_count[len]) {
code.bits = len;
code.value = symbols[idx++];
reps = 1 << (kJpegHuffmanRootTableBits - len);
while (reps--) {
table[key++] = code;
}
}
}
// Fill in 2nd level tables and add pointers to root table.
table += table_size;
table_size = 0;
low = 0;
for (len = kJpegHuffmanRootTableBits + 1;
len <= static_cast<int>(kJpegHuffmanMaxBitLength); ++len) {
for (; tmp_count[len] > 0; --tmp_count[len]) {
// Start a new sub-table if the previous one is full.
if (low >= table_size) {
table += table_size;
table_bits = NextTableBitSize(tmp_count, len);
table_size = 1 << table_bits;
low = 0;
lut[key].bits = table_bits + kJpegHuffmanRootTableBits;
lut[key].value = (table - lut) - key;
++key;
}
code.bits = len - kJpegHuffmanRootTableBits;
code.value = symbols[idx++];
reps = 1 << (table_bits - code.bits);
while (reps--) {
table[low++] = code;
}
}
}
}
} // namespace jpeg
} // namespace jxl
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