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src/Source/LibWebP/src/enc/enc.backward_references.c  view on Meta::CPAN

                              1 /* Low effort. */, hash_chain, refs_lz77)) {
    return NULL;
  }
  BackwardReferences2DLocality(width, refs_lz77);
  return refs_lz77;
}

static VP8LBackwardRefs* GetBackwardReferences(
    int width, int height, const uint32_t* const argb, int quality,
    int* const cache_bits, VP8LHashChain* const hash_chain,
    VP8LBackwardRefs refs_array[2]) {
  int lz77_is_useful;
  int lz77_computed;
  double bit_cost_lz77, bit_cost_rle;
  VP8LBackwardRefs* best = NULL;
  VP8LBackwardRefs* refs_lz77 = &refs_array[0];
  VP8LBackwardRefs* refs_rle = &refs_array[1];
  VP8LHistogram* histo = NULL;

  if (!CalculateBestCacheSize(argb, width, height, quality, hash_chain,
                              refs_lz77, &lz77_computed, cache_bits)) {
    goto Error;
  }

  if (lz77_computed) {
    // Transform refs_lz77 for the optimized cache_bits.
    if (*cache_bits > 0) {
      if (!BackwardRefsWithLocalCache(argb, *cache_bits, refs_lz77)) {
        goto Error;
      }
    }
  } else {
    if (!BackwardReferencesLz77(width, height, argb, *cache_bits, quality,
                                0 /* Low effort. */, hash_chain, refs_lz77)) {
      goto Error;
    }
  }

  if (!BackwardReferencesRle(width, height, argb, *cache_bits, refs_rle)) {
    goto Error;
  }

  histo = VP8LAllocateHistogram(*cache_bits);
  if (histo == NULL) goto Error;

  {
    // Evaluate LZ77 coding.
    VP8LHistogramCreate(histo, refs_lz77, *cache_bits);
    bit_cost_lz77 = VP8LHistogramEstimateBits(histo);
    // Evaluate RLE coding.
    VP8LHistogramCreate(histo, refs_rle, *cache_bits);
    bit_cost_rle = VP8LHistogramEstimateBits(histo);
    // Decide if LZ77 is useful.
    lz77_is_useful = (bit_cost_lz77 < bit_cost_rle);
  }

  // Choose appropriate backward reference.
  if (lz77_is_useful) {
    // TraceBackwards is costly. Don't execute it at lower quality.
    const int try_lz77_trace_backwards = (quality >= 25);
    best = refs_lz77;   // default guess: lz77 is better
    if (try_lz77_trace_backwards) {
      VP8LBackwardRefs* const refs_trace = refs_rle;
      if (!VP8LBackwardRefsCopy(refs_lz77, refs_trace)) {
        best = NULL;
        goto Error;
      }
      if (BackwardReferencesTraceBackwards(width, height, argb, quality,
                                           *cache_bits, hash_chain,
                                           refs_trace)) {
        double bit_cost_trace;
        // Evaluate LZ77 coding.
        VP8LHistogramCreate(histo, refs_trace, *cache_bits);
        bit_cost_trace = VP8LHistogramEstimateBits(histo);
        if (bit_cost_trace < bit_cost_lz77) {
          best = refs_trace;
        }
      }
    }
  } else {
    best = refs_rle;
  }

  BackwardReferences2DLocality(width, best);

 Error:
  VP8LFreeHistogram(histo);
  return best;
}

VP8LBackwardRefs* VP8LGetBackwardReferences(
    int width, int height, const uint32_t* const argb, int quality,
    int low_effort, int* const cache_bits, VP8LHashChain* const hash_chain,
    VP8LBackwardRefs refs_array[2]) {
  if (low_effort) {
    return GetBackwardReferencesLowEffort(width, height, argb, quality,
                                          cache_bits, hash_chain, refs_array);
  } else {
    return GetBackwardReferences(width, height, argb, quality, cache_bits,
                                 hash_chain, refs_array);
  }
}