src/math/remquof.c

   1 #include <math.h>
   2 #include <stdint.h>
   3
   4 float remquof(float x, float y, int *quo)
   5 {
   6         union {float f; uint32_t i;} ux = {x}, uy = {y};
   7         int ex = ux.i>>23 & 0xff;
   8         int ey = uy.i>>23 & 0xff;
   9         int sx = ux.i>>31;
  10         int sy = uy.i>>31;
  11         uint32_t q;
  12         uint32_t i;
  13         uint32_t uxi = ux.i;
  14
  15         *quo = 0;
  16         if (uy.i<<1 == 0 || isnan(y) || ex == 0xff)
  17                 return (x*y)/(x*y);
  18         if (ux.i<<1 == 0)
  19                 return x;
  20
  21         /* normalize x and y */
  22         if (!ex) {
  23                 for (i = uxi<<9; i>>31 == 0; ex--, i <<= 1);
  24                 uxi <<= -ex + 1;
  25         } else {
  26                 uxi &= -1U >> 9;
  27                 uxi |= 1U << 23;
  28         }
  29         if (!ey) {
  30                 for (i = uy.i<<9; i>>31 == 0; ey--, i <<= 1);
  31                 uy.i <<= -ey + 1;
  32         } else {
  33                 uy.i &= -1U >> 9;
  34                 uy.i |= 1U << 23;
  35         }
  36
  37         q = 0;
  38         if (ex < ey) {
  39                 if (ex+1 == ey)
  40                         goto end;
  41                 return x;
  42         }
  43
  44         /* x mod y */
  45         for (; ex > ey; ex--) {
  46                 i = uxi - uy.i;
  47                 if (i >> 31 == 0) {
  48                         uxi = i;
  49                         q++;
  50                 }
  51                 uxi <<= 1;
  52                 q <<= 1;
  53         }
  54         i = uxi - uy.i;
  55         if (i >> 31 == 0) {
  56                 uxi = i;
  57                 q++;
  58         }
  59         if (uxi == 0)
  60                 ex = -30;
  61         else
  62                 for (; uxi>>23 == 0; uxi <<= 1, ex--);
  63 end:
  64         /* scale result and decide between |x| and |x|-|y| */
  65         if (ex > 0) {
  66                 uxi -= 1U << 23;
  67                 uxi |= (uint32_t)ex << 23;
  68         } else {
  69                 uxi >>= -ex + 1;
  70         }
  71         ux.i = uxi;
  72         x = ux.f;
  73         if (sy)
  74                 y = -y;
  75         if (ex == ey || (ex+1 == ey && (2*x > y || (2*x == y && q%2)))) {
  76                 x -= y;
  77                 q++;
  78         }
  79         q &= 0x7fffffff;
  80         *quo = sx^sy ? -(int)q : (int)q;
  81         return sx ? -x : x;
  82 }