kc3-lang/brotli/c/enc/fast_log.h

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• Hash : 103b25fb
  Author :
  Date : 2025-08-13T02:10:36
  

  explicitly specify model for relocatable variables
  
  PiperOrigin-RevId: 794473371
  

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• c/enc/fast_log.h

• /* Copyright 2013 Google Inc. All Rights Reserved.
  
     Distributed under MIT license.
     See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
  */
  
  /* Utilities for fast computation of logarithms. */
  
  #ifndef BROTLI_ENC_FAST_LOG_H_
  #define BROTLI_ENC_FAST_LOG_H_
  
  #include <math.h>
  
  #include "../common/platform.h"
  
  #if defined(__cplusplus) || defined(c_plusplus)
  extern "C" {
  #endif
  
  static BROTLI_INLINE uint32_t Log2FloorNonZero(size_t n) {
  #if defined(BROTLI_BSR32)
    return BROTLI_BSR32((uint32_t)n);
  #else
    uint32_t result = 0;
    while (n >>= 1) result++;
    return result;
  #endif
  }
  
  #define BROTLI_LOG2_TABLE_SIZE 256
  
  /* A lookup table for small values of log2(int) to be used in entropy
     computation. */
  BROTLI_INTERNAL extern const BROTLI_MODEL("small")
  double kBrotliLog2Table[BROTLI_LOG2_TABLE_SIZE];
  
  /* Visual Studio 2012 and Android API levels < 18 do not have the log2()
   * function defined, so we use log() and a multiplication instead. */
  #if !defined(BROTLI_HAVE_LOG2)
  #if ((defined(_MSC_VER) && _MSC_VER <= 1700) || \
       (defined(__ANDROID_API__) && __ANDROID_API__ < 18))
  #define BROTLI_HAVE_LOG2 0
  #else
  #define BROTLI_HAVE_LOG2 1
  #endif
  #endif
  
  #define LOG_2_INV 1.4426950408889634
  
  /* Faster logarithm for small integers, with the property of log2(0) == 0. */
  static BROTLI_INLINE double FastLog2(size_t v) {
    if (v < BROTLI_LOG2_TABLE_SIZE) {
      return kBrotliLog2Table[v];
    }
  #if !(BROTLI_HAVE_LOG2)
    return log((double)v) * LOG_2_INV;
  #else
    return log2((double)v);
  #endif
  }
  
  #if defined(__cplusplus) || defined(c_plusplus)
  }  /* extern "C" */
  #endif
  
  #endif  /* BROTLI_ENC_FAST_LOG_H_ */
  

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