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Diffstat (limited to 'media/libwebp/utils/huffman_utils.c')
| -rw-r--r-- | media/libwebp/utils/huffman_utils.c | 223 |
1 files changed, 223 insertions, 0 deletions
diff --git a/media/libwebp/utils/huffman_utils.c b/media/libwebp/utils/huffman_utils.c new file mode 100644 index 000000000..008b5d746 --- /dev/null +++ b/media/libwebp/utils/huffman_utils.c @@ -0,0 +1,223 @@ +// Copyright 2012 Google Inc. All Rights Reserved. +// +// Use of this source code is governed by a BSD-style license +// that can be found in the COPYING file in the root of the source +// tree. An additional intellectual property rights grant can be found +// in the file PATENTS. All contributing project authors may +// be found in the AUTHORS file in the root of the source tree. +// ----------------------------------------------------------------------------- +// +// Utilities for building and looking up Huffman trees. +// +// Author: Urvang Joshi (urvang@google.com) + +#include <assert.h> +#include <stdlib.h> +#include <string.h> +#include "./huffman_utils.h" +#include "./utils.h" +#include "../webp/format_constants.h" + +// Huffman data read via DecodeImageStream is represented in two (red and green) +// bytes. +#define MAX_HTREE_GROUPS 0x10000 + +HTreeGroup* VP8LHtreeGroupsNew(int num_htree_groups) { + HTreeGroup* const htree_groups = + (HTreeGroup*)WebPSafeMalloc(num_htree_groups, sizeof(*htree_groups)); + if (htree_groups == NULL) { + return NULL; + } + assert(num_htree_groups <= MAX_HTREE_GROUPS); + return htree_groups; +} + +void VP8LHtreeGroupsFree(HTreeGroup* const htree_groups) { + if (htree_groups != NULL) { + WebPSafeFree(htree_groups); + } +} + +// Returns reverse(reverse(key, len) + 1, len), where reverse(key, len) is the +// bit-wise reversal of the len least significant bits of key. +static WEBP_INLINE uint32_t GetNextKey(uint32_t key, int len) { + uint32_t step = 1 << (len - 1); + while (key & step) { + step >>= 1; + } + return step ? (key & (step - 1)) + step : key; +} + +// Stores code in table[0], table[step], table[2*step], ..., table[end]. +// Assumes that end is an integer multiple of step. +static WEBP_INLINE void ReplicateValue(HuffmanCode* table, + int step, int end, + HuffmanCode code) { + assert(end % step == 0); + do { + end -= step; + table[end] = code; + } while (end > 0); +} + +// 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 WEBP_INLINE int NextTableBitSize(const int* const count, + int len, int root_bits) { + int left = 1 << (len - root_bits); + while (len < MAX_ALLOWED_CODE_LENGTH) { + left -= count[len]; + if (left <= 0) break; + ++len; + left <<= 1; + } + return len - root_bits; +} + +// sorted[code_lengths_size] is a pre-allocated array for sorting symbols +// by code length. +static int BuildHuffmanTable(HuffmanCode* const root_table, int root_bits, + const int code_lengths[], int code_lengths_size, + uint16_t sorted[]) { + HuffmanCode* table = root_table; // next available space in table + int total_size = 1 << root_bits; // total size root table + 2nd level table + int len; // current code length + int symbol; // symbol index in original or sorted table + // number of codes of each length: + int count[MAX_ALLOWED_CODE_LENGTH + 1] = { 0 }; + // offsets in sorted table for each length: + int offset[MAX_ALLOWED_CODE_LENGTH + 1]; + + assert(code_lengths_size != 0); + assert(code_lengths != NULL); + assert(root_table != NULL); + assert(root_bits > 0); + + // Build histogram of code lengths. + for (symbol = 0; symbol < code_lengths_size; ++symbol) { + if (code_lengths[symbol] > MAX_ALLOWED_CODE_LENGTH) { + return 0; + } + ++count[code_lengths[symbol]]; + } + + // Error, all code lengths are zeros. + if (count[0] == code_lengths_size) { + return 0; + } + + // Generate offsets into sorted symbol table by code length. + offset[1] = 0; + for (len = 1; len < MAX_ALLOWED_CODE_LENGTH; ++len) { + if (count[len] > (1 << len)) { + return 0; + } + offset[len + 1] = offset[len] + count[len]; + } + + // Sort symbols by length, by symbol order within each length. + for (symbol = 0; symbol < code_lengths_size; ++symbol) { + const int symbol_code_length = code_lengths[symbol]; + if (code_lengths[symbol] > 0) { + sorted[offset[symbol_code_length]++] = symbol; + } + } + + // Special case code with only one value. + if (offset[MAX_ALLOWED_CODE_LENGTH] == 1) { + HuffmanCode code; + code.bits = 0; + code.value = (uint16_t)sorted[0]; + ReplicateValue(table, 1, total_size, code); + return total_size; + } + + { + int step; // step size to replicate values in current table + uint32_t low = -1; // low bits for current root entry + uint32_t mask = total_size - 1; // mask for low bits + uint32_t key = 0; // reversed prefix code + int num_nodes = 1; // number of Huffman tree nodes + int num_open = 1; // number of open branches in current tree level + int table_bits = root_bits; // key length of current table + int table_size = 1 << table_bits; // size of current table + symbol = 0; + // Fill in root table. + for (len = 1, step = 2; len <= root_bits; ++len, step <<= 1) { + num_open <<= 1; + num_nodes += num_open; + num_open -= count[len]; + if (num_open < 0) { + return 0; + } + for (; count[len] > 0; --count[len]) { + HuffmanCode code; + code.bits = (uint8_t)len; + code.value = (uint16_t)sorted[symbol++]; + ReplicateValue(&table[key], step, table_size, code); + key = GetNextKey(key, len); + } + } + + // Fill in 2nd level tables and add pointers to root table. + for (len = root_bits + 1, step = 2; len <= MAX_ALLOWED_CODE_LENGTH; + ++len, step <<= 1) { + num_open <<= 1; + num_nodes += num_open; + num_open -= count[len]; + if (num_open < 0) { + return 0; + } + for (; count[len] > 0; --count[len]) { + HuffmanCode code; + if ((key & mask) != low) { + table += table_size; + table_bits = NextTableBitSize(count, len, root_bits); + table_size = 1 << table_bits; + total_size += table_size; + low = key & mask; + root_table[low].bits = (uint8_t)(table_bits + root_bits); + root_table[low].value = (uint16_t)((table - root_table) - low); + } + code.bits = (uint8_t)(len - root_bits); + code.value = (uint16_t)sorted[symbol++]; + ReplicateValue(&table[key >> root_bits], step, table_size, code); + key = GetNextKey(key, len); + } + } + + // Check if tree is full. + if (num_nodes != 2 * offset[MAX_ALLOWED_CODE_LENGTH] - 1) { + return 0; + } + } + + return total_size; +} + +// Maximum code_lengths_size is 2328 (reached for 11-bit color_cache_bits). +// More commonly, the value is around ~280. +#define MAX_CODE_LENGTHS_SIZE \ + ((1 << MAX_CACHE_BITS) + NUM_LITERAL_CODES + NUM_LENGTH_CODES) +// Cut-off value for switching between heap and stack allocation. +#define SORTED_SIZE_CUTOFF 512 +int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits, + const int code_lengths[], int code_lengths_size) { + int total_size; + assert(code_lengths_size <= MAX_CODE_LENGTHS_SIZE); + if (code_lengths_size <= SORTED_SIZE_CUTOFF) { + // use local stack-allocated array. + uint16_t sorted[SORTED_SIZE_CUTOFF]; + total_size = BuildHuffmanTable(root_table, root_bits, + code_lengths, code_lengths_size, sorted); + } else { // rare case. Use heap allocation. + uint16_t* const sorted = + (uint16_t*)WebPSafeMalloc(code_lengths_size, sizeof(*sorted)); + if (sorted == NULL) return 0; + total_size = BuildHuffmanTable(root_table, root_bits, + code_lengths, code_lengths_size, sorted); + WebPSafeFree(sorted); + } + return total_size; +} |