include/linux/int_log.h

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2 /*
   3  * Provides fixed-point logarithm operations.
   4  *
   5  * Copyright (C) 2006 Christoph Pfister (christophpfister@gmail.com)
   6  */
   7
   8 #ifndef __LINUX_INT_LOG_H
   9 #define __LINUX_INT_LOG_H
  10
  11 #include <linux/types.h>
  12
  13 /**
  14  * intlog2 - computes log2 of a value; the result is shifted left by 24 bits
  15  *
  16  * @value: The value (must be != 0)
  17  *
  18  * to use rational values you can use the following method:
  19  *
  20  *   intlog2(value) = intlog2(value * 2^x) - x * 2^24
  21  *
  22  * Some usecase examples:
  23  *
  24  *      intlog2(8) will give 3 << 24 = 3 * 2^24
  25  *
  26  *      intlog2(9) will give 3 << 24 + ... = 3.16... * 2^24
  27  *
  28  *      intlog2(1.5) = intlog2(3) - 2^24 = 0.584... * 2^24
  29  *
  30  *
  31  * return: log2(value) * 2^24
  32  */
  33 extern unsigned int intlog2(u32 value);
  34
  35 /**
  36  * intlog10 - computes log10 of a value; the result is shifted left by 24 bits
  37  *
  38  * @value: The value (must be != 0)
  39  *
  40  * to use rational values you can use the following method:
  41  *
  42  *   intlog10(value) = intlog10(value * 10^x) - x * 2^24
  43  *
  44  * An usecase example:
  45  *
  46  *      intlog10(1000) will give 3 << 24 = 3 * 2^24
  47  *
  48  *   due to the implementation intlog10(1000) might be not exactly 3 * 2^24
  49  *
  50  * look at intlog2 for similar examples
  51  *
  52  * return: log10(value) * 2^24
  53  */
  54 extern unsigned int intlog10(u32 value);
  55
  56 #endif