1/*
2Copyright 2011 Google Inc. All Rights Reserved.
3
4Licensed under the Apache License, Version 2.0 (the "License");
5you may not use this file except in compliance with the License.
6You may obtain a copy of the License at
7
8    http://www.apache.org/licenses/LICENSE-2.0
9
10Unless required by applicable law or agreed to in writing, software
11distributed under the License is distributed on an "AS IS" BASIS,
12WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13See the License for the specific language governing permissions and
14limitations under the License.
15
16Author: lode.vandevenne@gmail.com (Lode Vandevenne)
17Author: jyrki.alakuijala@gmail.com (Jyrki Alakuijala)
18*/
19
20#include "tree.h"
21
22#include <assert.h>
23#include <math.h>
24#include <stdio.h>
25#include <stdlib.h>
26
27#include "katajainen.h"
28#include "util.h"
29
30void ZopfliLengthsToSymbols(const unsigned* lengths, size_t n, unsigned maxbits,
31                            unsigned* symbols) {
32  size_t* bl_count = (size_t*)malloc(sizeof(size_t) * (maxbits + 1));
33  size_t* next_code = (size_t*)malloc(sizeof(size_t) * (maxbits + 1));
34  unsigned bits, i;
35  unsigned code;
36
37  for (i = 0; i < n; i++) {
38    symbols[i] = 0;
39  }
40
41  /* 1) Count the number of codes for each code length. Let bl_count[N] be the
42  number of codes of length N, N >= 1. */
43  for (bits = 0; bits <= maxbits; bits++) {
44    bl_count[bits] = 0;
45  }
46  for (i = 0; i < n; i++) {
47    assert(lengths[i] <= maxbits);
48    bl_count[lengths[i]]++;
49  }
50  /* 2) Find the numerical value of the smallest code for each code length. */
51  code = 0;
52  bl_count[0] = 0;
53  for (bits = 1; bits <= maxbits; bits++) {
54    code = (code + bl_count[bits-1]) << 1;
55    next_code[bits] = code;
56  }
57  /* 3) Assign numerical values to all codes, using consecutive values for all
58  codes of the same length with the base values determined at step 2. */
59  for (i = 0;  i < n; i++) {
60    unsigned len = lengths[i];
61    if (len != 0) {
62      symbols[i] = next_code[len];
63      next_code[len]++;
64    }
65  }
66
67  free(bl_count);
68  free(next_code);
69}
70
71void ZopfliCalculateEntropy(const size_t* count, size_t n, double* bitlengths) {
72  static const double kInvLog2 = 1.4426950408889;  /* 1.0 / log(2.0) */
73  unsigned sum = 0;
74  unsigned i;
75  double log2sum;
76  for (i = 0; i < n; ++i) {
77    sum += count[i];
78  }
79  log2sum = (sum == 0 ? log(n) : log(sum)) * kInvLog2;
80  for (i = 0; i < n; ++i) {
81    /* When the count of the symbol is 0, but its cost is requested anyway, it
82    means the symbol will appear at least once anyway, so give it the cost as if
83    its count is 1.*/
84    if (count[i] == 0) bitlengths[i] = log2sum;
85    else bitlengths[i] = log2sum - log(count[i]) * kInvLog2;
86    /* Depending on compiler and architecture, the above subtraction of two
87    floating point numbers may give a negative result very close to zero
88    instead of zero (e.g. -5.973954e-17 with gcc 4.1.2 on Ubuntu 11.4). Clamp
89    it to zero. These floating point imprecisions do not affect the cost model
90    significantly so this is ok. */
91    if (bitlengths[i] < 0 && bitlengths[i] > -1e-5) bitlengths[i] = 0;
92    assert(bitlengths[i] >= 0);
93  }
94}
95
96void ZopfliCalculateBitLengths(const size_t* count, size_t n, int maxbits,
97                               unsigned* bitlengths) {
98  int error = ZopfliLengthLimitedCodeLengths(count, n, maxbits, bitlengths);
99  (void) error;
100  assert(!error);
101}
102