contrib/openbsd_libm/src/e_fmodf.c

   1 /* e_fmodf.c -- float version of e_fmod.c.
   2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
   3  */
   4
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  */
  15
  16 /*
  17  * fmodf(x,y)
  18  * Return x mod y in exact arithmetic
  19  * Method: shift and subtract
  20  */
  21
  22 #include "math.h"
  23 #include "math_private.h"
  24
  25 static const float one = 1.0, Zero[] = {0.0, -0.0,};
  26
  27 float
  28 fmodf(float x, float y)
  29 {
  30         int32_t n,hx,hy,hz,ix,iy,sx,i;
  31
  32         GET_FLOAT_WORD(hx,x);
  33         GET_FLOAT_WORD(hy,y);
  34         sx = hx&0x80000000;             /* sign of x */
  35         hx ^=sx;                /* |x| */
  36         hy &= 0x7fffffff;       /* |y| */
  37
  38     /* purge off exception values */
  39         if(hy==0||(hx>=0x7f800000)||            /* y=0,or x not finite */
  40            (hy>0x7f800000))                     /* or y is NaN */
  41             return (x*y)/(x*y);
  42         if(hx<hy) return x;                     /* |x|<|y| return x */
  43         if(hx==hy)
  44             return Zero[(u_int32_t)sx>>31];     /* |x|=|y| return x*0*/
  45
  46     /* determine ix = ilogb(x) */
  47         if(hx<0x00800000) {     /* subnormal x */
  48             for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
  49         } else ix = (hx>>23)-127;
  50
  51     /* determine iy = ilogb(y) */
  52         if(hy<0x00800000) {     /* subnormal y */
  53             for (iy = -126,i=(hy<<8); i>=0; i<<=1) iy -=1;
  54         } else iy = (hy>>23)-127;
  55
  56     /* set up {hx,lx}, {hy,ly} and align y to x */
  57         if(ix >= -126)
  58             hx = 0x00800000|(0x007fffff&hx);
  59         else {          /* subnormal x, shift x to normal */
  60             n = -126-ix;
  61             hx = hx<<n;
  62         }
  63         if(iy >= -126)
  64             hy = 0x00800000|(0x007fffff&hy);
  65         else {          /* subnormal y, shift y to normal */
  66             n = -126-iy;
  67             hy = hy<<n;
  68         }
  69
  70     /* fix point fmod */
  71         n = ix - iy;
  72         while(n--) {
  73             hz=hx-hy;
  74             if(hz<0){hx = hx+hx;}
  75             else {
  76                 if(hz==0)               /* return sign(x)*0 */
  77                     return Zero[(u_int32_t)sx>>31];
  78                 hx = hz+hz;
  79             }
  80         }
  81         hz=hx-hy;
  82         if(hz>=0) {hx=hz;}
  83
  84     /* convert back to floating value and restore the sign */
  85         if(hx==0)                       /* return sign(x)*0 */
  86             return Zero[(u_int32_t)sx>>31];
  87         while(hx<0x00800000) {          /* normalize x */
  88             hx = hx+hx;
  89             iy -= 1;
  90         }
  91         if(iy>= -126) {         /* normalize output */
  92             hx = ((hx-0x00800000)|((iy+127)<<23));
  93             SET_FLOAT_WORD(x,hx|sx);
  94         } else {                /* subnormal output */
  95             n = -126 - iy;
  96             hx >>= n;
  97             SET_FLOAT_WORD(x,hx|sx);
  98             x *= one;           /* create necessary signal */
  99         }
 100         return x;               /* exact output */
 101 }