apps/codecs/libatrac/fixp_math.c

   1 #include "fixp_math.h"
   2
   3 inline int32_t fixmul31(int32_t x, int32_t y)
   4 {
   5     int64_t temp;
   6     temp = x;
   7     temp *= y;
   8
   9     temp >>= 31;        //16+31-16 = 31 bits
  10
  11     return (int32_t)temp;
  12 }
  13
  14 /*
  15  * Fast integer square root adapted from algorithm,
  16  * Martin Guy @ UKC, June 1985.
  17  * Originally from a book on programming abaci by Mr C. Woo.
  18  * This is taken from :
  19  * http://wiki.forum.nokia.com/index.php/How_to_use_fixed_point_maths#How_to_get_square_root_for_integers
  20  * with a added shift up of the result by 8 bits to return result in 16.16 fixed-point representation.
  21  */
  22 inline int32_t fastSqrt(int32_t n)
  23 {
  24    /*
  25     * Logically, these are unsigned.
  26     * We need the sign bit to test
  27     *   whether (op - res - one) underflowed.
  28     */
  29     int32_t op, res, one;
  30     op = n;
  31     res = 0;
  32     /* "one" starts at the highest power of four <= than the argument. */
  33     one = 1 << 30;      /* second-to-top bit set */
  34     while (one > op) one >>= 2;
  35     while (one != 0)
  36     {
  37         if (op >= res + one)
  38         {
  39             op = op - (res + one);
  40             res = res +  (one<<1);
  41         }
  42         res >>= 1;
  43         one >>= 2;
  44     }
  45     return(res << 8);
  46 }
  47
  48 inline int32_t fixmul16(int32_t x, int32_t y)
  49 {
  50     int64_t temp;
  51     temp = x;
  52     temp *= y;
  53
  54     temp >>= 16;
  55
  56     return (int32_t)temp;
  57 }
  58
  59 inline int32_t fixdiv16(int32_t x, int32_t y)
  60 {
  61     int64_t temp;
  62     temp = x << 16;
  63     temp /= y;
  64
  65     return (int32_t)temp;
  66 }