libwebp: update snapshot to v0.2.0-rc1

third_party/libwebp/enc/histogram.c

+// Copyright 2012 Google Inc. All Rights Reserved.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Author: Jyrki Alakuijala (jyrki@google.com)
+//
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <math.h>
+#include <stdio.h>
+
+#include "./backward_references.h"
+#include "./histogram.h"
+#include "../dsp/lossless.h"
+#include "../utils/utils.h"
+
+static void HistogramClear(VP8LHistogram* const p) {
+  memset(p->literal_, 0, sizeof(p->literal_));
+  memset(p->red_, 0, sizeof(p->red_));
+  memset(p->blue_, 0, sizeof(p->blue_));
+  memset(p->alpha_, 0, sizeof(p->alpha_));
+  memset(p->distance_, 0, sizeof(p->distance_));
+  p->bit_cost_ = 0;
+}
+
+void VP8LHistogramStoreRefs(const VP8LBackwardRefs* const refs,
+                            VP8LHistogram* const histo) {
+  int i;
+  for (i = 0; i < refs->size; ++i) {
+    VP8LHistogramAddSinglePixOrCopy(histo, &refs->refs[i]);
+  }
+}
+
+void VP8LHistogramCreate(VP8LHistogram* const p,
+                         const VP8LBackwardRefs* const refs,
+                         int palette_code_bits) {
+  if (palette_code_bits >= 0) {
+    p->palette_code_bits_ = palette_code_bits;
+  }
+  HistogramClear(p);
+  VP8LHistogramStoreRefs(refs, p);
+}
+
+void VP8LHistogramInit(VP8LHistogram* const p, int palette_code_bits) {
+  p->palette_code_bits_ = palette_code_bits;
+  HistogramClear(p);
+}
+
+VP8LHistogramSet* VP8LAllocateHistogramSet(int size, int cache_bits) {
+  int i;
+  VP8LHistogramSet* set;
+  VP8LHistogram* bulk;
+  const uint64_t total_size = (uint64_t)sizeof(*set)
+                            + size * sizeof(*set->histograms)
+                            + size * sizeof(**set->histograms);
+  uint8_t* memory = (uint8_t*)WebPSafeMalloc(total_size, sizeof(*memory));
+  if (memory == NULL) return NULL;
+
+  set = (VP8LHistogramSet*)memory;
+  memory += sizeof(*set);
+  set->histograms = (VP8LHistogram**)memory;
+  memory += size * sizeof(*set->histograms);
+  bulk = (VP8LHistogram*)memory;
+  set->max_size = size;
+  set->size = size;
+  for (i = 0; i < size; ++i) {
+    set->histograms[i] = bulk + i;
+    VP8LHistogramInit(set->histograms[i], cache_bits);
+  }
+  return set;
+}
+
+// -----------------------------------------------------------------------------
+
+void VP8LHistogramAddSinglePixOrCopy(VP8LHistogram* const histo,
+                                     const PixOrCopy* const v) {
+  if (PixOrCopyIsLiteral(v)) {
+    ++histo->alpha_[PixOrCopyLiteral(v, 3)];
+    ++histo->red_[PixOrCopyLiteral(v, 2)];
+    ++histo->literal_[PixOrCopyLiteral(v, 1)];
+    ++histo->blue_[PixOrCopyLiteral(v, 0)];
+  } else if (PixOrCopyIsCacheIdx(v)) {
+    int literal_ix = 256 + NUM_LENGTH_CODES + PixOrCopyCacheIdx(v);
+    ++histo->literal_[literal_ix];
+  } else {
+    int code, extra_bits_count, extra_bits_value;
+    PrefixEncode(PixOrCopyLength(v),
+                 &code, &extra_bits_count, &extra_bits_value);
+    ++histo->literal_[256 + code];
+    PrefixEncode(PixOrCopyDistance(v),
+                 &code, &extra_bits_count, &extra_bits_value);
+    ++histo->distance_[code];
+  }
+}
+
+
+
+static double BitsEntropy(const int* const array, int n) {
+  double retval = 0.;
+  int sum = 0;
+  int nonzeros = 0;
+  int max_val = 0;
+  int i;
+  double mix;
+  for (i = 0; i < n; ++i) {
+    if (array[i] != 0) {
+      sum += array[i];
+      ++nonzeros;
+      retval -= VP8LFastSLog2(array[i]);
+      if (max_val < array[i]) {
+        max_val = array[i];
+      }
+    }
+  }
+  retval += VP8LFastSLog2(sum);
+
+  if (nonzeros < 5) {
+    if (nonzeros <= 1) {
+      return 0;
+    }
+    // Two symbols, they will be 0 and 1 in a Huffman code.
+    // Let's mix in a bit of entropy to favor good clustering when
+    // distributions of these are combined.
+    if (nonzeros == 2) {
+      return 0.99 * sum + 0.01 * retval;
+    }
+    // No matter what the entropy says, we cannot be better than min_limit
+    // with Huffman coding. I am mixing a bit of entropy into the
+    // min_limit since it produces much better (~0.5 %) compression results
+    // perhaps because of better entropy clustering.
+    if (nonzeros == 3) {
+      mix = 0.95;
+    } else {
+      mix = 0.7;  // nonzeros == 4.
+    }
+  } else {
+    mix = 0.627;
+  }
+
+  {
+    double min_limit = 2 * sum - max_val;
+    min_limit = mix * min_limit + (1.0 - mix) * retval;
+    return (retval < min_limit) ? min_limit : retval;
+  }
+}
+
+double VP8LHistogramEstimateBitsBulk(const VP8LHistogram* const p) {
+  double retval = BitsEntropy(&p->literal_[0], VP8LHistogramNumCodes(p))
+                + BitsEntropy(&p->red_[0], 256)
+                + BitsEntropy(&p->blue_[0], 256)
+                + BitsEntropy(&p->alpha_[0], 256)
+                + BitsEntropy(&p->distance_[0], NUM_DISTANCE_CODES);
+  // Compute the extra bits cost.
+  int i;
+  for (i = 2; i < NUM_LENGTH_CODES - 2; ++i) {
+    retval +=
+        (i >> 1) * p->literal_[256 + i + 2];
+  }
+  for (i = 2; i < NUM_DISTANCE_CODES - 2; ++i) {
+    retval += (i >> 1) * p->distance_[i + 2];
+  }
+  return retval;
+}
+
+
+// Returns the cost encode the rle-encoded entropy code.
+// The constants in this function are experimental.
+static double HuffmanCost(const int* const population, int length) {
+  // Small bias because Huffman code length is typically not stored in
+  // full length.
+  static const int kHuffmanCodeOfHuffmanCodeSize = CODE_LENGTH_CODES * 3;
+  static const double kSmallBias = 9.1;
+  double retval = kHuffmanCodeOfHuffmanCodeSize - kSmallBias;
+  int streak = 0;
+  int i = 0;
+  for (; i < length - 1; ++i) {
+    ++streak;
+    if (population[i] == population[i + 1]) {
+      continue;
+    }
+ last_streak_hack:
+    // population[i] points now to the symbol in the streak of same values.
+    if (streak > 3) {
+      if (population[i] == 0) {
+        retval += 1.5625 + 0.234375 * streak;
+      } else {
+        retval += 2.578125 + 0.703125 * streak;
+      }
+    } else {
+      if (population[i] == 0) {
+        retval += 1.796875 * streak;
+      } else {
+        retval += 3.28125 * streak;
+      }
+    }
+    streak = 0;
+  }
+  if (i == length - 1) {
+    ++streak;
+    goto last_streak_hack;
+  }
+  return retval;
+}
+
+// Estimates the Huffman dictionary + other block overhead size.
+static double HistogramEstimateBitsHeader(const VP8LHistogram* const p) {
+  return HuffmanCost(&p->alpha_[0], 256) +
+         HuffmanCost(&p->red_[0], 256) +
+         HuffmanCost(&p->literal_[0], VP8LHistogramNumCodes(p)) +
+         HuffmanCost(&p->blue_[0], 256) +
+         HuffmanCost(&p->distance_[0], NUM_DISTANCE_CODES);
+}
+
+double VP8LHistogramEstimateBits(const VP8LHistogram* const p) {
+  return HistogramEstimateBitsHeader(p) + VP8LHistogramEstimateBitsBulk(p);
+}
+
+static void HistogramBuildImage(int xsize, int histo_bits,
+                                const VP8LBackwardRefs* const backward_refs,
+                                VP8LHistogramSet* const image) {
+  int i;
+  int x = 0, y = 0;
+  const int histo_xsize = VP8LSubSampleSize(xsize, histo_bits);
+  VP8LHistogram** const histograms = image->histograms;
+  assert(histo_bits > 0);
+  for (i = 0; i < backward_refs->size; ++i) {
+    const PixOrCopy* const v = &backward_refs->refs[i];
+    const int ix = (y >> histo_bits) * histo_xsize + (x >> histo_bits);
+    VP8LHistogramAddSinglePixOrCopy(histograms[ix], v);
+    x += PixOrCopyLength(v);
+    while (x >= xsize) {
+      x -= xsize;
+      ++y;
+    }
+  }
+}
+
+static uint32_t MyRand(uint32_t *seed) {
+  *seed *= 16807U;
+  if (*seed == 0) {
+    *seed = 1;
+  }
+  return *seed;
+}
+
+static int HistogramCombine(const VP8LHistogramSet* const in,
+                            VP8LHistogramSet* const out, int num_pairs) {
+  int ok = 0;
+  int i, iter;
+  uint32_t seed = 0;
+  int tries_with_no_success = 0;
+  const int min_cluster_size = 2;
+  int out_size = in->size;
+  const int outer_iters = in->size * 3;
+  VP8LHistogram* const histos = (VP8LHistogram*)malloc(2 * sizeof(*histos));
+  VP8LHistogram* cur_combo = histos + 0;    // trial merged histogram
+  VP8LHistogram* best_combo = histos + 1;   // best merged histogram so far
+  if (histos == NULL) goto End;
+
+  // Copy histograms from in[] to out[].
+  assert(in->size <= out->size);
+  for (i = 0; i < in->size; ++i) {
+    in->histograms[i]->bit_cost_ = VP8LHistogramEstimateBits(in->histograms[i]);
+    *out->histograms[i] = *in->histograms[i];
+  }
+
+  // Collapse similar histograms in 'out'.
+  for (iter = 0; iter < outer_iters && out_size >= min_cluster_size; ++iter) {
+    // We pick the best pair to be combined out of 'inner_iters' pairs.
+    double best_cost_diff = 0.;
+    int best_idx1 = 0, best_idx2 = 1;
+    int j;
+    seed += iter;
+    for (j = 0; j < num_pairs; ++j) {
+      double curr_cost_diff;
+      // Choose two histograms at random and try to combine them.
+      const uint32_t idx1 = MyRand(&seed) % out_size;
+      const uint32_t tmp = ((j & 7) + 1) % (out_size - 1);
+      const uint32_t diff = (tmp < 3) ? tmp : MyRand(&seed) % (out_size - 1);
+      const uint32_t idx2 = (idx1 + diff + 1) % out_size;
+      if (idx1 == idx2) {
+        continue;
+      }
+      *cur_combo = *out->histograms[idx1];
+      VP8LHistogramAdd(cur_combo, out->histograms[idx2]);
+      cur_combo->bit_cost_ = VP8LHistogramEstimateBits(cur_combo);
+      // Calculate cost reduction on combining.
+      curr_cost_diff = cur_combo->bit_cost_
+                     - out->histograms[idx1]->bit_cost_
+                     - out->histograms[idx2]->bit_cost_;
+      if (best_cost_diff > curr_cost_diff) {    // found a better pair?
+        {     // swap cur/best combo histograms
+          VP8LHistogram* const tmp_histo = cur_combo;
+          cur_combo = best_combo;
+          best_combo = tmp_histo;
+        }
+        best_cost_diff = curr_cost_diff;
+        best_idx1 = idx1;
+        best_idx2 = idx2;
+      }
+    }
+
+    if (best_cost_diff < 0.0) {
+      *out->histograms[best_idx1] = *best_combo;
+      // swap best_idx2 slot with last one (which is now unused)
+      --out_size;
+      if (best_idx2 != out_size) {
+        out->histograms[best_idx2] = out->histograms[out_size];
+        out->histograms[out_size] = NULL;   // just for sanity check.
+      }
+      tries_with_no_success = 0;
+    }
+    if (++tries_with_no_success >= 50) {
+      break;
+    }
+  }
+  out->size = out_size;
+  ok = 1;
+
+ End:
+  free(histos);
+  return ok;
+}
+
+// -----------------------------------------------------------------------------
+// Histogram refinement
+
+// What is the bit cost of moving square_histogram from
+// cur_symbol to candidate_symbol.
+// TODO(skal): we don't really need to copy the histogram and Add(). Instead
+// we just need VP8LDualHistogramEstimateBits(A, B) estimation function.
+static double HistogramDistance(const VP8LHistogram* const square_histogram,
+                                const VP8LHistogram* const candidate) {
+  const double previous_bit_cost = candidate->bit_cost_;
+  double new_bit_cost;
+  VP8LHistogram modified_histo;
+  modified_histo = *candidate;
+  VP8LHistogramAdd(&modified_histo, square_histogram);
+  new_bit_cost = VP8LHistogramEstimateBits(&modified_histo);
+
+  return new_bit_cost - previous_bit_cost;
+}
+
+// Find the best 'out' histogram for each of the 'in' histograms.
+// Note: we assume that out[]->bit_cost_ is already up-to-date.
+static void HistogramRemap(const VP8LHistogramSet* const in,
+                           const VP8LHistogramSet* const out,
+                           uint16_t* const symbols) {
+  int i;
+  for (i = 0; i < in->size; ++i) {
+    int best_out = 0;
+    double best_bits = HistogramDistance(in->histograms[i], out->histograms[0]);
+    int k;
+    for (k = 1; k < out->size; ++k) {
+      const double cur_bits =
+          HistogramDistance(in->histograms[i], out->histograms[k]);
+      if (cur_bits < best_bits) {
+        best_bits = cur_bits;
+        best_out = k;
+      }
+    }
+    symbols[i] = best_out;
+  }
+
+  // Recompute each out based on raw and symbols.
+  for (i = 0; i < out->size; ++i) {
+    HistogramClear(out->histograms[i]);
+  }
+  for (i = 0; i < in->size; ++i) {
+    VP8LHistogramAdd(out->histograms[symbols[i]], in->histograms[i]);
+  }
+}
+
+int VP8LGetHistoImageSymbols(int xsize, int ysize,
+                             const VP8LBackwardRefs* const refs,
+                             int quality, int histo_bits, int cache_bits,
+                             VP8LHistogramSet* const image_in,
+                             uint16_t* const histogram_symbols) {
+  int ok = 0;
+  const int histo_xsize = histo_bits ? VP8LSubSampleSize(xsize, histo_bits) : 1;
+  const int histo_ysize = histo_bits ? VP8LSubSampleSize(ysize, histo_bits) : 1;
+  const int num_histo_pairs = 10 + quality / 2;  // For HistogramCombine().
+  const int histo_image_raw_size = histo_xsize * histo_ysize;
+  VP8LHistogramSet* const image_out =
+      VP8LAllocateHistogramSet(histo_image_raw_size, cache_bits);
+  if (image_out == NULL) return 0;
+
+  // Build histogram image.
+  HistogramBuildImage(xsize, histo_bits, refs, image_out);
+  // Collapse similar histograms.
+  if (!HistogramCombine(image_out, image_in, num_histo_pairs)) {
+    goto Error;
+  }
+  // Find the optimal map from original histograms to the final ones.
+  HistogramRemap(image_out, image_in, histogram_symbols);
+  ok = 1;
+
+Error:
+  free(image_out);
+  return ok;
+}