| /* NOLINT(build/header_guard) */ |
| /* Copyright 2013 Google Inc. All Rights Reserved. |
| |
| Distributed under MIT license. |
| See file LICENSE for detail or copy at https://opensource.org/licenses/MIT |
| */ |
| |
| /* template parameters: FN, CODE */ |
| |
| #define HistogramType FN(Histogram) |
| |
| /* Computes the bit cost reduction by combining out[idx1] and out[idx2] and if |
| it is below a threshold, stores the pair (idx1, idx2) in the *pairs queue. */ |
| BROTLI_INTERNAL void FN(BrotliCompareAndPushToQueue)( |
| const HistogramType* out, const uint32_t* cluster_size, uint32_t idx1, |
| uint32_t idx2, size_t max_num_pairs, HistogramPair* pairs, |
| size_t* num_pairs) CODE({ |
| BROTLI_BOOL is_good_pair = BROTLI_FALSE; |
| HistogramPair p; |
| p.idx1 = p.idx2 = 0; |
| p.cost_diff = p.cost_combo = 0; |
| if (idx1 == idx2) { |
| return; |
| } |
| if (idx2 < idx1) { |
| uint32_t t = idx2; |
| idx2 = idx1; |
| idx1 = t; |
| } |
| p.idx1 = idx1; |
| p.idx2 = idx2; |
| p.cost_diff = 0.5 * ClusterCostDiff(cluster_size[idx1], cluster_size[idx2]); |
| p.cost_diff -= out[idx1].bit_cost_; |
| p.cost_diff -= out[idx2].bit_cost_; |
| |
| if (out[idx1].total_count_ == 0) { |
| p.cost_combo = out[idx2].bit_cost_; |
| is_good_pair = BROTLI_TRUE; |
| } else if (out[idx2].total_count_ == 0) { |
| p.cost_combo = out[idx1].bit_cost_; |
| is_good_pair = BROTLI_TRUE; |
| } else { |
| double threshold = *num_pairs == 0 ? 1e99 : |
| BROTLI_MAX(double, 0.0, pairs[0].cost_diff); |
| HistogramType combo = out[idx1]; |
| double cost_combo; |
| FN(HistogramAddHistogram)(&combo, &out[idx2]); |
| cost_combo = FN(BrotliPopulationCost)(&combo); |
| if (cost_combo < threshold - p.cost_diff) { |
| p.cost_combo = cost_combo; |
| is_good_pair = BROTLI_TRUE; |
| } |
| } |
| if (is_good_pair) { |
| p.cost_diff += p.cost_combo; |
| if (*num_pairs > 0 && HistogramPairIsLess(&pairs[0], &p)) { |
| /* Replace the top of the queue if needed. */ |
| if (*num_pairs < max_num_pairs) { |
| pairs[*num_pairs] = pairs[0]; |
| ++(*num_pairs); |
| } |
| pairs[0] = p; |
| } else if (*num_pairs < max_num_pairs) { |
| pairs[*num_pairs] = p; |
| ++(*num_pairs); |
| } |
| } |
| }) |
| |
| BROTLI_INTERNAL size_t FN(BrotliHistogramCombine)(HistogramType* out, |
| uint32_t* cluster_size, |
| uint32_t* symbols, |
| uint32_t* clusters, |
| HistogramPair* pairs, |
| size_t num_clusters, |
| size_t symbols_size, |
| size_t max_clusters, |
| size_t max_num_pairs) CODE({ |
| double cost_diff_threshold = 0.0; |
| size_t min_cluster_size = 1; |
| size_t num_pairs = 0; |
| |
| { |
| /* We maintain a vector of histogram pairs, with the property that the pair |
| with the maximum bit cost reduction is the first. */ |
| size_t idx1; |
| for (idx1 = 0; idx1 < num_clusters; ++idx1) { |
| size_t idx2; |
| for (idx2 = idx1 + 1; idx2 < num_clusters; ++idx2) { |
| FN(BrotliCompareAndPushToQueue)(out, cluster_size, clusters[idx1], |
| clusters[idx2], max_num_pairs, &pairs[0], &num_pairs); |
| } |
| } |
| } |
| |
| while (num_clusters > min_cluster_size) { |
| uint32_t best_idx1; |
| uint32_t best_idx2; |
| size_t i; |
| if (pairs[0].cost_diff >= cost_diff_threshold) { |
| cost_diff_threshold = 1e99; |
| min_cluster_size = max_clusters; |
| continue; |
| } |
| /* Take the best pair from the top of heap. */ |
| best_idx1 = pairs[0].idx1; |
| best_idx2 = pairs[0].idx2; |
| FN(HistogramAddHistogram)(&out[best_idx1], &out[best_idx2]); |
| out[best_idx1].bit_cost_ = pairs[0].cost_combo; |
| cluster_size[best_idx1] += cluster_size[best_idx2]; |
| for (i = 0; i < symbols_size; ++i) { |
| if (symbols[i] == best_idx2) { |
| symbols[i] = best_idx1; |
| } |
| } |
| for (i = 0; i < num_clusters; ++i) { |
| if (clusters[i] == best_idx2) { |
| memmove(&clusters[i], &clusters[i + 1], |
| (num_clusters - i - 1) * sizeof(clusters[0])); |
| break; |
| } |
| } |
| --num_clusters; |
| { |
| /* Remove pairs intersecting the just combined best pair. */ |
| size_t copy_to_idx = 0; |
| for (i = 0; i < num_pairs; ++i) { |
| HistogramPair* p = &pairs[i]; |
| if (p->idx1 == best_idx1 || p->idx2 == best_idx1 || |
| p->idx1 == best_idx2 || p->idx2 == best_idx2) { |
| /* Remove invalid pair from the queue. */ |
| continue; |
| } |
| if (HistogramPairIsLess(&pairs[0], p)) { |
| /* Replace the top of the queue if needed. */ |
| HistogramPair front = pairs[0]; |
| pairs[0] = *p; |
| pairs[copy_to_idx] = front; |
| } else { |
| pairs[copy_to_idx] = *p; |
| } |
| ++copy_to_idx; |
| } |
| num_pairs = copy_to_idx; |
| } |
| |
| /* Push new pairs formed with the combined histogram to the heap. */ |
| for (i = 0; i < num_clusters; ++i) { |
| FN(BrotliCompareAndPushToQueue)(out, cluster_size, best_idx1, clusters[i], |
| max_num_pairs, &pairs[0], &num_pairs); |
| } |
| } |
| return num_clusters; |
| }) |
| |
| /* What is the bit cost of moving histogram from cur_symbol to candidate. */ |
| BROTLI_INTERNAL double FN(BrotliHistogramBitCostDistance)( |
| const HistogramType* histogram, const HistogramType* candidate) CODE({ |
| if (histogram->total_count_ == 0) { |
| return 0.0; |
| } else { |
| HistogramType tmp = *histogram; |
| FN(HistogramAddHistogram)(&tmp, candidate); |
| return FN(BrotliPopulationCost)(&tmp) - candidate->bit_cost_; |
| } |
| }) |
| |
| /* Find the best 'out' histogram for each of the 'in' histograms. |
| When called, clusters[0..num_clusters) contains the unique values from |
| symbols[0..in_size), but this property is not preserved in this function. |
| Note: we assume that out[]->bit_cost_ is already up-to-date. */ |
| BROTLI_INTERNAL void FN(BrotliHistogramRemap)(const HistogramType* in, |
| size_t in_size, const uint32_t* clusters, size_t num_clusters, |
| HistogramType* out, uint32_t* symbols) CODE({ |
| size_t i; |
| for (i = 0; i < in_size; ++i) { |
| uint32_t best_out = i == 0 ? symbols[0] : symbols[i - 1]; |
| double best_bits = |
| FN(BrotliHistogramBitCostDistance)(&in[i], &out[best_out]); |
| size_t j; |
| for (j = 0; j < num_clusters; ++j) { |
| const double cur_bits = |
| FN(BrotliHistogramBitCostDistance)(&in[i], &out[clusters[j]]); |
| if (cur_bits < best_bits) { |
| best_bits = cur_bits; |
| best_out = clusters[j]; |
| } |
| } |
| symbols[i] = best_out; |
| } |
| |
| /* Recompute each out based on raw and symbols. */ |
| for (i = 0; i < num_clusters; ++i) { |
| FN(HistogramClear)(&out[clusters[i]]); |
| } |
| for (i = 0; i < in_size; ++i) { |
| FN(HistogramAddHistogram)(&out[symbols[i]], &in[i]); |
| } |
| }) |
| |
| /* Reorders elements of the out[0..length) array and changes values in |
| symbols[0..length) array in the following way: |
| * when called, symbols[] contains indexes into out[], and has N unique |
| values (possibly N < length) |
| * on return, symbols'[i] = f(symbols[i]) and |
| out'[symbols'[i]] = out[symbols[i]], for each 0 <= i < length, |
| where f is a bijection between the range of symbols[] and [0..N), and |
| the first occurrences of values in symbols'[i] come in consecutive |
| increasing order. |
| Returns N, the number of unique values in symbols[]. */ |
| BROTLI_INTERNAL size_t FN(BrotliHistogramReindex)(MemoryManager* m, |
| HistogramType* out, uint32_t* symbols, size_t length) CODE({ |
| static const uint32_t kInvalidIndex = BROTLI_UINT32_MAX; |
| uint32_t* new_index = BROTLI_ALLOC(m, uint32_t, length); |
| uint32_t next_index; |
| HistogramType* tmp; |
| size_t i; |
| if (BROTLI_IS_OOM(m)) return 0; |
| for (i = 0; i < length; ++i) { |
| new_index[i] = kInvalidIndex; |
| } |
| next_index = 0; |
| for (i = 0; i < length; ++i) { |
| if (new_index[symbols[i]] == kInvalidIndex) { |
| new_index[symbols[i]] = next_index; |
| ++next_index; |
| } |
| } |
| /* TODO: by using idea of "cycle-sort" we can avoid allocation of |
| tmp and reduce the number of copying by the factor of 2. */ |
| tmp = BROTLI_ALLOC(m, HistogramType, next_index); |
| if (BROTLI_IS_OOM(m)) return 0; |
| next_index = 0; |
| for (i = 0; i < length; ++i) { |
| if (new_index[symbols[i]] == next_index) { |
| tmp[next_index] = out[symbols[i]]; |
| ++next_index; |
| } |
| symbols[i] = new_index[symbols[i]]; |
| } |
| BROTLI_FREE(m, new_index); |
| for (i = 0; i < next_index; ++i) { |
| out[i] = tmp[i]; |
| } |
| BROTLI_FREE(m, tmp); |
| return next_index; |
| }) |
| |
| BROTLI_INTERNAL void FN(BrotliClusterHistograms)( |
| MemoryManager* m, const HistogramType* in, const size_t in_size, |
| size_t max_histograms, HistogramType* out, size_t* out_size, |
| uint32_t* histogram_symbols) CODE({ |
| uint32_t* cluster_size = BROTLI_ALLOC(m, uint32_t, in_size); |
| uint32_t* clusters = BROTLI_ALLOC(m, uint32_t, in_size); |
| size_t num_clusters = 0; |
| const size_t max_input_histograms = 64; |
| size_t pairs_capacity = max_input_histograms * max_input_histograms / 2; |
| /* For the first pass of clustering, we allow all pairs. */ |
| HistogramPair* pairs = BROTLI_ALLOC(m, HistogramPair, pairs_capacity + 1); |
| size_t i; |
| |
| if (BROTLI_IS_OOM(m)) return; |
| |
| for (i = 0; i < in_size; ++i) { |
| cluster_size[i] = 1; |
| } |
| |
| for (i = 0; i < in_size; ++i) { |
| out[i] = in[i]; |
| out[i].bit_cost_ = FN(BrotliPopulationCost)(&in[i]); |
| histogram_symbols[i] = (uint32_t)i; |
| } |
| |
| for (i = 0; i < in_size; i += max_input_histograms) { |
| size_t num_to_combine = |
| BROTLI_MIN(size_t, in_size - i, max_input_histograms); |
| size_t num_new_clusters; |
| size_t j; |
| for (j = 0; j < num_to_combine; ++j) { |
| clusters[num_clusters + j] = (uint32_t)(i + j); |
| } |
| num_new_clusters = |
| FN(BrotliHistogramCombine)(out, cluster_size, |
| &histogram_symbols[i], |
| &clusters[num_clusters], pairs, |
| num_to_combine, num_to_combine, |
| max_histograms, pairs_capacity); |
| num_clusters += num_new_clusters; |
| } |
| |
| { |
| /* For the second pass, we limit the total number of histogram pairs. |
| After this limit is reached, we only keep searching for the best pair. */ |
| size_t max_num_pairs = BROTLI_MIN(size_t, |
| 64 * num_clusters, (num_clusters / 2) * num_clusters); |
| BROTLI_ENSURE_CAPACITY( |
| m, HistogramPair, pairs, pairs_capacity, max_num_pairs + 1); |
| if (BROTLI_IS_OOM(m)) return; |
| |
| /* Collapse similar histograms. */ |
| num_clusters = FN(BrotliHistogramCombine)(out, cluster_size, |
| histogram_symbols, clusters, |
| pairs, num_clusters, in_size, |
| max_histograms, max_num_pairs); |
| } |
| BROTLI_FREE(m, pairs); |
| BROTLI_FREE(m, cluster_size); |
| /* Find the optimal map from original histograms to the final ones. */ |
| FN(BrotliHistogramRemap)(in, in_size, clusters, num_clusters, |
| out, histogram_symbols); |
| BROTLI_FREE(m, clusters); |
| /* Convert the context map to a canonical form. */ |
| *out_size = FN(BrotliHistogramReindex)(m, out, histogram_symbols, in_size); |
| if (BROTLI_IS_OOM(m)) return; |
| }) |
| |
| #undef HistogramType |
