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brotli/c/enc/quality.h  view on Meta::CPAN

/* Copyright 2016 Google Inc. All Rights Reserved.

   Distributed under MIT license.
   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/

/* Constants and formulas that affect speed-ratio trade-offs and thus define
   quality levels. */

#ifndef BROTLI_ENC_QUALITY_H_
#define BROTLI_ENC_QUALITY_H_

#include "../common/platform.h"
#include <brotli/encode.h>
#include "./params.h"

#define FAST_ONE_PASS_COMPRESSION_QUALITY 0
#define FAST_TWO_PASS_COMPRESSION_QUALITY 1
#define ZOPFLIFICATION_QUALITY 10
#define HQ_ZOPFLIFICATION_QUALITY 11

#define MAX_QUALITY_FOR_STATIC_ENTROPY_CODES 2
#define MIN_QUALITY_FOR_BLOCK_SPLIT 4
#define MIN_QUALITY_FOR_NONZERO_DISTANCE_PARAMS 4
#define MIN_QUALITY_FOR_OPTIMIZE_HISTOGRAMS 4
#define MIN_QUALITY_FOR_EXTENSIVE_REFERENCE_SEARCH 5
#define MIN_QUALITY_FOR_CONTEXT_MODELING 5
#define MIN_QUALITY_FOR_HQ_CONTEXT_MODELING 7
#define MIN_QUALITY_FOR_HQ_BLOCK_SPLITTING 10

/* For quality below MIN_QUALITY_FOR_BLOCK_SPLIT there is no block splitting,
   so we buffer at most this much literals and commands. */
#define MAX_NUM_DELAYED_SYMBOLS 0x2FFF

/* Returns hash-table size for quality levels 0 and 1. */
static BROTLI_INLINE size_t MaxHashTableSize(int quality) {
  return quality == FAST_ONE_PASS_COMPRESSION_QUALITY ? 1 << 15 : 1 << 17;
}

/* The maximum length for which the zopflification uses distinct distances. */
#define MAX_ZOPFLI_LEN_QUALITY_10 150
#define MAX_ZOPFLI_LEN_QUALITY_11 325

/* Do not thoroughly search when a long copy is found. */
#define BROTLI_LONG_COPY_QUICK_STEP 16384

static BROTLI_INLINE size_t MaxZopfliLen(const BrotliEncoderParams* params) {
  return params->quality <= 10 ?
      MAX_ZOPFLI_LEN_QUALITY_10 :
      MAX_ZOPFLI_LEN_QUALITY_11;
}

/* Number of best candidates to evaluate to expand Zopfli chain. */
static BROTLI_INLINE size_t MaxZopfliCandidates(
  const BrotliEncoderParams* params) {
  return params->quality <= 10 ? 1 : 5;
}

static BROTLI_INLINE void SanitizeParams(BrotliEncoderParams* params) {
  params->quality = BROTLI_MIN(int, BROTLI_MAX_QUALITY,
      BROTLI_MAX(int, BROTLI_MIN_QUALITY, params->quality));
  if (params->quality <= MAX_QUALITY_FOR_STATIC_ENTROPY_CODES) {
    params->large_window = BROTLI_FALSE;
  }
  if (params->lgwin < BROTLI_MIN_WINDOW_BITS) {
    params->lgwin = BROTLI_MIN_WINDOW_BITS;
  } else {