diff options
Diffstat (limited to 'src/main/jni/libwebp/utils/huffman_encode.c')
| -rw-r--r-- | src/main/jni/libwebp/utils/huffman_encode.c | 417 |
1 files changed, 0 insertions, 417 deletions
diff --git a/src/main/jni/libwebp/utils/huffman_encode.c b/src/main/jni/libwebp/utils/huffman_encode.c deleted file mode 100644 index 6421c2bee..000000000 --- a/src/main/jni/libwebp/utils/huffman_encode.c +++ /dev/null @@ -1,417 +0,0 @@ -// Copyright 2011 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. -// ----------------------------------------------------------------------------- -// -// Author: Jyrki Alakuijala (jyrki@google.com) -// -// Entropy encoding (Huffman) for webp lossless. - -#include <assert.h> -#include <stdlib.h> -#include <string.h> -#include "./huffman_encode.h" -#include "../utils/utils.h" -#include "../webp/format_constants.h" - -// ----------------------------------------------------------------------------- -// Util function to optimize the symbol map for RLE coding - -// Heuristics for selecting the stride ranges to collapse. -static int ValuesShouldBeCollapsedToStrideAverage(int a, int b) { - return abs(a - b) < 4; -} - -// Change the population counts in a way that the consequent -// Huffman tree compression, especially its RLE-part, give smaller output. -static void OptimizeHuffmanForRle(int length, uint8_t* const good_for_rle, - uint32_t* const counts) { - // 1) Let's make the Huffman code more compatible with rle encoding. - int i; - for (; length >= 0; --length) { - if (length == 0) { - return; // All zeros. - } - if (counts[length - 1] != 0) { - // Now counts[0..length - 1] does not have trailing zeros. - break; - } - } - // 2) Let's mark all population counts that already can be encoded - // with an rle code. - { - // Let's not spoil any of the existing good rle codes. - // Mark any seq of 0's that is longer as 5 as a good_for_rle. - // Mark any seq of non-0's that is longer as 7 as a good_for_rle. - uint32_t symbol = counts[0]; - int stride = 0; - for (i = 0; i < length + 1; ++i) { - if (i == length || counts[i] != symbol) { - if ((symbol == 0 && stride >= 5) || - (symbol != 0 && stride >= 7)) { - int k; - for (k = 0; k < stride; ++k) { - good_for_rle[i - k - 1] = 1; - } - } - stride = 1; - if (i != length) { - symbol = counts[i]; - } - } else { - ++stride; - } - } - } - // 3) Let's replace those population counts that lead to more rle codes. - { - uint32_t stride = 0; - uint32_t limit = counts[0]; - uint32_t sum = 0; - for (i = 0; i < length + 1; ++i) { - if (i == length || good_for_rle[i] || - (i != 0 && good_for_rle[i - 1]) || - !ValuesShouldBeCollapsedToStrideAverage(counts[i], limit)) { - if (stride >= 4 || (stride >= 3 && sum == 0)) { - uint32_t k; - // The stride must end, collapse what we have, if we have enough (4). - uint32_t count = (sum + stride / 2) / stride; - if (count < 1) { - count = 1; - } - if (sum == 0) { - // Don't make an all zeros stride to be upgraded to ones. - count = 0; - } - for (k = 0; k < stride; ++k) { - // We don't want to change value at counts[i], - // that is already belonging to the next stride. Thus - 1. - counts[i - k - 1] = count; - } - } - stride = 0; - sum = 0; - if (i < length - 3) { - // All interesting strides have a count of at least 4, - // at least when non-zeros. - limit = (counts[i] + counts[i + 1] + - counts[i + 2] + counts[i + 3] + 2) / 4; - } else if (i < length) { - limit = counts[i]; - } else { - limit = 0; - } - } - ++stride; - if (i != length) { - sum += counts[i]; - if (stride >= 4) { - limit = (sum + stride / 2) / stride; - } - } - } - } -} - -// A comparer function for two Huffman trees: sorts first by 'total count' -// (more comes first), and then by 'value' (more comes first). -static int CompareHuffmanTrees(const void* ptr1, const void* ptr2) { - const HuffmanTree* const t1 = (const HuffmanTree*)ptr1; - const HuffmanTree* const t2 = (const HuffmanTree*)ptr2; - if (t1->total_count_ > t2->total_count_) { - return -1; - } else if (t1->total_count_ < t2->total_count_) { - return 1; - } else { - assert(t1->value_ != t2->value_); - return (t1->value_ < t2->value_) ? -1 : 1; - } -} - -static void SetBitDepths(const HuffmanTree* const tree, - const HuffmanTree* const pool, - uint8_t* const bit_depths, int level) { - if (tree->pool_index_left_ >= 0) { - SetBitDepths(&pool[tree->pool_index_left_], pool, bit_depths, level + 1); - SetBitDepths(&pool[tree->pool_index_right_], pool, bit_depths, level + 1); - } else { - bit_depths[tree->value_] = level; - } -} - -// Create an optimal Huffman tree. -// -// (data,length): population counts. -// tree_limit: maximum bit depth (inclusive) of the codes. -// bit_depths[]: how many bits are used for the symbol. -// -// Returns 0 when an error has occurred. -// -// The catch here is that the tree cannot be arbitrarily deep -// -// count_limit is the value that is to be faked as the minimum value -// and this minimum value is raised until the tree matches the -// maximum length requirement. -// -// This algorithm is not of excellent performance for very long data blocks, -// especially when population counts are longer than 2**tree_limit, but -// we are not planning to use this with extremely long blocks. -// -// See http://en.wikipedia.org/wiki/Huffman_coding -static void GenerateOptimalTree(const uint32_t* const histogram, - int histogram_size, - HuffmanTree* tree, int tree_depth_limit, - uint8_t* const bit_depths) { - uint32_t count_min; - HuffmanTree* tree_pool; - int tree_size_orig = 0; - int i; - - for (i = 0; i < histogram_size; ++i) { - if (histogram[i] != 0) { - ++tree_size_orig; - } - } - - if (tree_size_orig == 0) { // pretty optimal already! - return; - } - - tree_pool = tree + tree_size_orig; - - // For block sizes with less than 64k symbols we never need to do a - // second iteration of this loop. - // If we actually start running inside this loop a lot, we would perhaps - // be better off with the Katajainen algorithm. - assert(tree_size_orig <= (1 << (tree_depth_limit - 1))); - for (count_min = 1; ; count_min *= 2) { - int tree_size = tree_size_orig; - // We need to pack the Huffman tree in tree_depth_limit bits. - // So, we try by faking histogram entries to be at least 'count_min'. - int idx = 0; - int j; - for (j = 0; j < histogram_size; ++j) { - if (histogram[j] != 0) { - const uint32_t count = - (histogram[j] < count_min) ? count_min : histogram[j]; - tree[idx].total_count_ = count; - tree[idx].value_ = j; - tree[idx].pool_index_left_ = -1; - tree[idx].pool_index_right_ = -1; - ++idx; - } - } - - // Build the Huffman tree. - qsort(tree, tree_size, sizeof(*tree), CompareHuffmanTrees); - - if (tree_size > 1) { // Normal case. - int tree_pool_size = 0; - while (tree_size > 1) { // Finish when we have only one root. - uint32_t count; - tree_pool[tree_pool_size++] = tree[tree_size - 1]; - tree_pool[tree_pool_size++] = tree[tree_size - 2]; - count = tree_pool[tree_pool_size - 1].total_count_ + - tree_pool[tree_pool_size - 2].total_count_; - tree_size -= 2; - { - // Search for the insertion point. - int k; - for (k = 0; k < tree_size; ++k) { - if (tree[k].total_count_ <= count) { - break; - } - } - memmove(tree + (k + 1), tree + k, (tree_size - k) * sizeof(*tree)); - tree[k].total_count_ = count; - tree[k].value_ = -1; - - tree[k].pool_index_left_ = tree_pool_size - 1; - tree[k].pool_index_right_ = tree_pool_size - 2; - tree_size = tree_size + 1; - } - } - SetBitDepths(&tree[0], tree_pool, bit_depths, 0); - } else if (tree_size == 1) { // Trivial case: only one element. - bit_depths[tree[0].value_] = 1; - } - - { - // Test if this Huffman tree satisfies our 'tree_depth_limit' criteria. - int max_depth = bit_depths[0]; - for (j = 1; j < histogram_size; ++j) { - if (max_depth < bit_depths[j]) { - max_depth = bit_depths[j]; - } - } - if (max_depth <= tree_depth_limit) { - break; - } - } - } -} - -// ----------------------------------------------------------------------------- -// Coding of the Huffman tree values - -static HuffmanTreeToken* CodeRepeatedValues(int repetitions, - HuffmanTreeToken* tokens, - int value, int prev_value) { - assert(value <= MAX_ALLOWED_CODE_LENGTH); - if (value != prev_value) { - tokens->code = value; - tokens->extra_bits = 0; - ++tokens; - --repetitions; - } - while (repetitions >= 1) { - if (repetitions < 3) { - int i; - for (i = 0; i < repetitions; ++i) { - tokens->code = value; - tokens->extra_bits = 0; - ++tokens; - } - break; - } else if (repetitions < 7) { - tokens->code = 16; - tokens->extra_bits = repetitions - 3; - ++tokens; - break; - } else { - tokens->code = 16; - tokens->extra_bits = 3; - ++tokens; - repetitions -= 6; - } - } - return tokens; -} - -static HuffmanTreeToken* CodeRepeatedZeros(int repetitions, - HuffmanTreeToken* tokens) { - while (repetitions >= 1) { - if (repetitions < 3) { - int i; - for (i = 0; i < repetitions; ++i) { - tokens->code = 0; // 0-value - tokens->extra_bits = 0; - ++tokens; - } - break; - } else if (repetitions < 11) { - tokens->code = 17; - tokens->extra_bits = repetitions - 3; - ++tokens; - break; - } else if (repetitions < 139) { - tokens->code = 18; - tokens->extra_bits = repetitions - 11; - ++tokens; - break; - } else { - tokens->code = 18; - tokens->extra_bits = 0x7f; // 138 repeated 0s - ++tokens; - repetitions -= 138; - } - } - return tokens; -} - -int VP8LCreateCompressedHuffmanTree(const HuffmanTreeCode* const tree, - HuffmanTreeToken* tokens, int max_tokens) { - HuffmanTreeToken* const starting_token = tokens; - HuffmanTreeToken* const ending_token = tokens + max_tokens; - const int depth_size = tree->num_symbols; - int prev_value = 8; // 8 is the initial value for rle. - int i = 0; - assert(tokens != NULL); - while (i < depth_size) { - const int value = tree->code_lengths[i]; - int k = i + 1; - int runs; - while (k < depth_size && tree->code_lengths[k] == value) ++k; - runs = k - i; - if (value == 0) { - tokens = CodeRepeatedZeros(runs, tokens); - } else { - tokens = CodeRepeatedValues(runs, tokens, value, prev_value); - prev_value = value; - } - i += runs; - assert(tokens <= ending_token); - } - (void)ending_token; // suppress 'unused variable' warning - return (int)(tokens - starting_token); -} - -// ----------------------------------------------------------------------------- - -// Pre-reversed 4-bit values. -static const uint8_t kReversedBits[16] = { - 0x0, 0x8, 0x4, 0xc, 0x2, 0xa, 0x6, 0xe, - 0x1, 0x9, 0x5, 0xd, 0x3, 0xb, 0x7, 0xf -}; - -static uint32_t ReverseBits(int num_bits, uint32_t bits) { - uint32_t retval = 0; - int i = 0; - while (i < num_bits) { - i += 4; - retval |= kReversedBits[bits & 0xf] << (MAX_ALLOWED_CODE_LENGTH + 1 - i); - bits >>= 4; - } - retval >>= (MAX_ALLOWED_CODE_LENGTH + 1 - num_bits); - return retval; -} - -// Get the actual bit values for a tree of bit depths. -static void ConvertBitDepthsToSymbols(HuffmanTreeCode* const tree) { - // 0 bit-depth means that the symbol does not exist. - int i; - int len; - uint32_t next_code[MAX_ALLOWED_CODE_LENGTH + 1]; - int depth_count[MAX_ALLOWED_CODE_LENGTH + 1] = { 0 }; - - assert(tree != NULL); - len = tree->num_symbols; - for (i = 0; i < len; ++i) { - const int code_length = tree->code_lengths[i]; - assert(code_length <= MAX_ALLOWED_CODE_LENGTH); - ++depth_count[code_length]; - } - depth_count[0] = 0; // ignore unused symbol - next_code[0] = 0; - { - uint32_t code = 0; - for (i = 1; i <= MAX_ALLOWED_CODE_LENGTH; ++i) { - code = (code + depth_count[i - 1]) << 1; - next_code[i] = code; - } - } - for (i = 0; i < len; ++i) { - const int code_length = tree->code_lengths[i]; - tree->codes[i] = ReverseBits(code_length, next_code[code_length]++); - } -} - -// ----------------------------------------------------------------------------- -// Main entry point - -void VP8LCreateHuffmanTree(uint32_t* const histogram, int tree_depth_limit, - uint8_t* const buf_rle, - HuffmanTree* const huff_tree, - HuffmanTreeCode* const huff_code) { - const int num_symbols = huff_code->num_symbols; - memset(buf_rle, 0, num_symbols * sizeof(*buf_rle)); - OptimizeHuffmanForRle(num_symbols, buf_rle, histogram); - GenerateOptimalTree(histogram, num_symbols, huff_tree, tree_depth_limit, - huff_code->code_lengths); - // Create the actual bit codes for the bit lengths. - ConvertBitDepthsToSymbols(huff_code); -} |