drivers/media/dvb-core/dvb_math.h

   1 /*
   2  * dvb-math provides some complex fixed-point math
   3  * operations shared between the dvb related stuff
   4  *
   5  * Copyright (C) 2006 Christoph Pfister (christophpfister@gmail.com)
   6  *
   7  * This library is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU Lesser General Public License as
   9  * published by the Free Software Foundation; either version 2.1 of
  10  * the License, or (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  15  * GNU Lesser General Public License for more details.
  16  */
  17
  18 #ifndef __DVB_MATH_H
  19 #define __DVB_MATH_H
  20
  21 #include <linux/types.h>
  22
  23 /**
  24  * intlog2 - computes log2 of a value; the result is shifted left by 24 bits
  25  *
  26  * @value: The value (must be != 0)
  27  *
  28  * to use rational values you can use the following method:
  29  *
  30  *   intlog2(value) = intlog2(value * 2^x) - x * 2^24
  31  *
  32  * Some usecase examples:
  33  *
  34  *      intlog2(8) will give 3 << 24 = 3 * 2^24
  35  *
  36  *      intlog2(9) will give 3 << 24 + ... = 3.16... * 2^24
  37  *
  38  *      intlog2(1.5) = intlog2(3) - 2^24 = 0.584... * 2^24
  39  *
  40  *
  41  * return: log2(value) * 2^24
  42  */
  43 extern unsigned int intlog2(u32 value);
  44
  45 /**
  46  * intlog10 - computes log10 of a value; the result is shifted left by 24 bits
  47  *
  48  * @value: The value (must be != 0)
  49  *
  50  * to use rational values you can use the following method:
  51  *
  52  *   intlog10(value) = intlog10(value * 10^x) - x * 2^24
  53  *
  54  * An usecase example:
  55  *
  56  *      intlog10(1000) will give 3 << 24 = 3 * 2^24
  57  *
  58  *   due to the implementation intlog10(1000) might be not exactly 3 * 2^24
  59  *
  60  * look at intlog2 for similar examples
  61  *
  62  * return: log10(value) * 2^24
  63  */
  64 extern unsigned int intlog10(u32 value);
  65
  66 #endif