1 files changed, 127 insertions, 0 deletions
diff --git a/c/enc/bit_cost_inc.h b/c/enc/bit_cost_inc.h
new file mode 100644
index 0000000..453c226
--- /dev/null
+++ b/c/enc/bit_cost_inc.h
@@ -0,0 +1,127 @@
+/* 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 */
+
+#define HistogramType FN(Histogram)
+
+double FN(BrotliPopulationCost)(const HistogramType* histogram) {
+  static const double kOneSymbolHistogramCost = 12;
+  static const double kTwoSymbolHistogramCost = 20;
+  static const double kThreeSymbolHistogramCost = 28;
+  static const double kFourSymbolHistogramCost = 37;
+  const size_t data_size = FN(HistogramDataSize)();
+  int count = 0;
+  size_t s[5];
+  double bits = 0.0;
+  size_t i;
+  if (histogram->total_count_ == 0) {
+    return kOneSymbolHistogramCost;
+  }
+  for (i = 0; i < data_size; ++i) {
+    if (histogram->data_[i] > 0) {
+      s[count] = i;
+      ++count;
+      if (count > 4) break;
+    }
+  }
+  if (count == 1) {
+    return kOneSymbolHistogramCost;
+  }
+  if (count == 2) {
+    return (kTwoSymbolHistogramCost + (double)histogram->total_count_);
+  }
+  if (count == 3) {
+    const uint32_t histo0 = histogram->data_[s[0]];
+    const uint32_t histo1 = histogram->data_[s[1]];
+    const uint32_t histo2 = histogram->data_[s[2]];
+    const uint32_t histomax =
+        BROTLI_MAX(uint32_t, histo0, BROTLI_MAX(uint32_t, histo1, histo2));
+    return (kThreeSymbolHistogramCost +
+            2 * (histo0 + histo1 + histo2) - histomax);
+  }
+  if (count == 4) {
+    uint32_t histo[4];
+    uint32_t h23;
+    uint32_t histomax;
+    for (i = 0; i < 4; ++i) {
+      histo[i] = histogram->data_[s[i]];
+    }
+    /* Sort */
+    for (i = 0; i < 4; ++i) {
+      size_t j;
+      for (j = i + 1; j < 4; ++j) {
+        if (histo[j] > histo[i]) {
+          BROTLI_SWAP(uint32_t, histo, j, i);
+        }
+      }
+    }
+    h23 = histo[2] + histo[3];
+    histomax = BROTLI_MAX(uint32_t, h23, histo[0]);
+    return (kFourSymbolHistogramCost +
+            3 * h23 + 2 * (histo[0] + histo[1]) - histomax);
+  }
+
+  {
+    /* In this loop we compute the entropy of the histogram and simultaneously
+       build a simplified histogram of the code length codes where we use the
+       zero repeat code 17, but we don't use the non-zero repeat code 16. */
+    size_t max_depth = 1;
+    uint32_t depth_histo[BROTLI_CODE_LENGTH_CODES] = { 0 };
+    const double log2total = FastLog2(histogram->total_count_);
+    for (i = 0; i < data_size;) {
+      if (histogram->data_[i] > 0) {
+        /* Compute -log2(P(symbol)) = -log2(count(symbol)/total_count) =
+                                    = log2(total_count) - log2(count(symbol)) */
+        double log2p = log2total - FastLog2(histogram->data_[i]);
+        /* Approximate the bit depth by round(-log2(P(symbol))) */
+        size_t depth = (size_t)(log2p + 0.5);
+        bits += histogram->data_[i] * log2p;
+        if (depth > 15) {
+          depth = 15;
+        }
+        if (depth > max_depth) {
+          max_depth = depth;
+        }
+        ++depth_histo[depth];
+        ++i;
+      } else {
+        /* Compute the run length of zeros and add the appropriate number of 0
+           and 17 code length codes to the code length code histogram. */
+        uint32_t reps = 1;
+        size_t k;
+        for (k = i + 1; k < data_size && histogram->data_[k] == 0; ++k) {
+          ++reps;
+        }
+        i += reps;
+        if (i == data_size) {
+          /* Don't add any cost for the last zero run, since these are encoded
+             only implicitly. */
+          break;
+        }
+        if (reps < 3) {
+          depth_histo[0] += reps;
+        } else {
+          reps -= 2;
+          while (reps > 0) {
+            ++depth_histo[BROTLI_REPEAT_ZERO_CODE_LENGTH];
+            /* Add the 3 extra bits for the 17 code length code. */
+            bits += 3;
+            reps >>= 3;
+          }
+        }
+      }
+    }
+    /* Add the estimated encoding cost of the code length code histogram. */
+    bits += (double)(18 + 2 * max_depth);
+    /* Add the entropy of the code length code histogram. */
+    bits += BitsEntropy(depth_histo, BROTLI_CODE_LENGTH_CODES);
+  }
+  return bits;
+}
+
+#undef HistogramType