libwebp: update snapshot to v0.2.0-rc1

third_party/libwebp/utils/huffman_encode.c

+// Copyright 2011 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)
+//
+// 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
+// Hufmann tree compression, especially its RLE-part, give smaller output.
+static int OptimizeHuffmanForRle(int length, int* const counts) {
+  uint8_t* good_for_rle;
+  // 1) Let's make the Huffman code more compatible with rle encoding.
+  int i;
+  for (; length >= 0; --length) {
+    if (length == 0) {
+      return 1;  // 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.
+  good_for_rle = (uint8_t*)calloc(length, 1);
+  if (good_for_rle == NULL) {
+    return 0;
+  }
+  {
+    // 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.
+    int 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.
+  {
+    int stride = 0;
+    int limit = counts[0];
+    int 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)) {
+          int k;
+          // The stride must end, collapse what we have, if we have enough (4).
+          int 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;
+        }
+      }
+    }
+  }
+  free(good_for_rle);
+  return 1;
+}
+
+typedef struct {
+  int total_count_;
+  int value_;
+  int pool_index_left_;
+  int pool_index_right_;
+} HuffmanTree;
+
+// 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 {
+    if (t1->value_ < t2->value_) {
+      return -1;
+    }
+    if (t1->value_ > t2->value_) {
+      return 1;
+    }
+    return 0;
+  }
+}
+
+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 int GenerateOptimalTree(const int* const histogram, int histogram_size,
+                               int tree_depth_limit,
+                               uint8_t* const bit_depths) {
+  int count_min;
+  HuffmanTree* tree_pool;
+  HuffmanTree* tree;
+  int tree_size_orig = 0;
+  int i;
+
+  for (i = 0; i < histogram_size; ++i) {
+    if (histogram[i] != 0) {
+      ++tree_size_orig;
+    }
+  }
+
+  // 3 * tree_size is enough to cover all the nodes representing a
+  // population and all the inserted nodes combining two existing nodes.
+  // The tree pool needs 2 * (tree_size_orig - 1) entities, and the
+  // tree needs exactly tree_size_orig entities.
+  tree = (HuffmanTree*)WebPSafeMalloc(3ULL * tree_size_orig, sizeof(*tree));
+  if (tree == NULL) return 0;
+  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 int 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.
+        int 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;
+      }
+    }
+  }
+  free(tree);
+  return 1;
+}
+
+// -----------------------------------------------------------------------------
+// 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
+
+int VP8LCreateHuffmanTree(int* const histogram, int tree_depth_limit,
+                          HuffmanTreeCode* const tree) {
+  const int num_symbols = tree->num_symbols;
+  if (!OptimizeHuffmanForRle(num_symbols, histogram)) {
+    return 0;
+  }
+  if (!GenerateOptimalTree(histogram, num_symbols,
+                           tree_depth_limit, tree->code_lengths)) {
+    return 0;
+  }
+  // Create the actual bit codes for the bit lengths.
+  ConvertBitDepthsToSymbols(tree);
+  return 1;
+}