BaseTools/Source/C/BrotliCompress/enc/quality.h

   1 /* Copyright 2016 Google Inc. All Rights Reserved.
   2
   3    Distributed under MIT license.
   4    See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
   5 */
   6
   7 /* Constants and formulas that affect speed-ratio trade-offs and thus define
   8    quality levels. */
   9
  10 #ifndef BROTLI_ENC_QUALITY_H_
  11 #define BROTLI_ENC_QUALITY_H_
  12
  13 #include "./encode.h"
  14
  15 #define FAST_ONE_PASS_COMPRESSION_QUALITY 0
  16 #define FAST_TWO_PASS_COMPRESSION_QUALITY 1
  17 #define ZOPFLIFICATION_QUALITY 10
  18 #define HQ_ZOPFLIFICATION_QUALITY 11
  19
  20 #define MAX_QUALITY_FOR_STATIC_ENRTOPY_CODES 2
  21 #define MIN_QUALITY_FOR_BLOCK_SPLIT 4
  22 #define MIN_QUALITY_FOR_OPTIMIZE_HISTOGRAMS 4
  23 #define MIN_QUALITY_FOR_EXTENSIVE_REFERENCE_SEARCH 5
  24 #define MIN_QUALITY_FOR_CONTEXT_MODELING 5
  25 #define MIN_QUALITY_FOR_HQ_CONTEXT_MODELING 7
  26 #define MIN_QUALITY_FOR_HQ_BLOCK_SPLITTING 10
  27 /* Only for "font" mode. */
  28 #define MIN_QUALITY_FOR_RECOMPUTE_DISTANCE_PREFIXES 10
  29
  30 /* For quality below MIN_QUALITY_FOR_BLOCK_SPLIT there is no block splitting,
  31    so we buffer at most this much literals and commands. */
  32 #define MAX_NUM_DELAYED_SYMBOLS 0x2fff
  33
  34 /* Encoding parameters */
  35 typedef struct BrotliEncoderParams {
  36   BrotliEncoderMode mode;
  37   int quality;
  38   int lgwin;
  39   int lgblock;
  40 } BrotliEncoderParams;
  41
  42 /* Returns hashtable size for quality levels 0 and 1. */
  43 static BROTLI_INLINE size_t MaxHashTableSize(int quality) {
  44   return quality == FAST_ONE_PASS_COMPRESSION_QUALITY ? 1 << 15 : 1 << 17;
  45 }
  46
  47 /* The maximum length for which the zopflification uses distinct distances. */
  48 #define MAX_ZOPFLI_LEN_QUALITY_10 150
  49 #define MAX_ZOPFLI_LEN_QUALITY_11 325
  50
  51 static BROTLI_INLINE size_t MaxZopfliLen(const BrotliEncoderParams* params) {
  52   return params->quality <= 10 ?
  53       MAX_ZOPFLI_LEN_QUALITY_10 :
  54       MAX_ZOPFLI_LEN_QUALITY_11;
  55 }
  56
  57 /* Number of best candidates to evaluate to expand zopfli chain. */
  58 static BROTLI_INLINE size_t MaxZopfliCandidates(
  59   const BrotliEncoderParams* params) {
  60   return params->quality <= 10 ? 1 : 5;
  61 }
  62
  63 static BROTLI_INLINE void SanitizeParams(BrotliEncoderParams* params) {
  64   params->quality = BROTLI_MIN(int, BROTLI_MAX_QUALITY,
  65       BROTLI_MAX(int, BROTLI_MIN_QUALITY, params->quality));
  66   if (params->lgwin < kBrotliMinWindowBits) {
  67     params->lgwin = kBrotliMinWindowBits;
  68   } else if (params->lgwin > kBrotliMaxWindowBits) {
  69     params->lgwin = kBrotliMaxWindowBits;
  70   }
  71 }
  72
  73 /* Returns optimized lg_block value. */
  74 static BROTLI_INLINE int ComputeLgBlock(const BrotliEncoderParams* params) {
  75   int lgblock = params->lgblock;
  76   if (params->quality == FAST_ONE_PASS_COMPRESSION_QUALITY ||
  77       params->quality == FAST_TWO_PASS_COMPRESSION_QUALITY) {
  78     lgblock = params->lgwin;
  79   } else if (params->quality < MIN_QUALITY_FOR_BLOCK_SPLIT) {
  80     lgblock = 14;
  81   } else if (lgblock == 0) {
  82     lgblock = 16;
  83     if (params->quality >= 9 && params->lgwin > lgblock) {
  84       lgblock = BROTLI_MIN(int, 18, params->lgwin);
  85     }
  86   } else {
  87     lgblock = BROTLI_MIN(int, kBrotliMaxInputBlockBits,
  88         BROTLI_MAX(int, kBrotliMinInputBlockBits, lgblock));
  89   }
  90   return lgblock;
  91 }
  92
  93 /* Returns log2 of the size of main ring buffer area.
  94    Allocate at least lgwin + 1 bits for the ring buffer so that the newly
  95    added block fits there completely and we still get lgwin bits and at least
  96    read_block_size_bits + 1 bits because the copy tail length needs to be
  97    smaller than ringbuffer size. */
  98 static BROTLI_INLINE int ComputeRbBits(const BrotliEncoderParams* params) {
  99   return 1 + BROTLI_MAX(int, params->lgwin, params->lgblock);
 100 }
 101
 102 static BROTLI_INLINE size_t MaxMetablockSize(
 103     const BrotliEncoderParams* params) {
 104   int bits = BROTLI_MIN(int, ComputeRbBits(params), kBrotliMaxInputBlockBits);
 105   return (size_t)1 << bits;
 106 }
 107
 108 /* When searching for backward references and have not seen matches for a long
 109    time, we can skip some match lookups. Unsuccessful match lookups are very
 110    expensive and this kind of a heuristic speeds up compression quite a lot.
 111    At first 8 byte strides are taken and every second byte is put to hasher.
 112    After 4x more literals stride by 16 bytes, every put 4-th byte to hasher.
 113    Applied only to qualities 2 to 9. */
 114 static BROTLI_INLINE size_t LiteralSpreeLengthForSparseSearch(
 115     const BrotliEncoderParams* params) {
 116   return params->quality < 9 ? 64 : 512;
 117 }
 118
 119 static BROTLI_INLINE int ChooseHasher(const BrotliEncoderParams* params) {
 120   if (params->quality > 9) {
 121     return 10;
 122   } else if (params->quality < 5) {
 123     return params->quality;
 124   } else if (params->lgwin <= 16) {
 125     return params->quality < 7 ? 40 : params->quality < 9 ? 41 : 42;
 126   }
 127   return params->quality;
 128 }
 129
 130 #endif  /* BROTLI_ENC_QUALITY_H_ */