compiler/stdc/math/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 #ifndef lint
  17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_fmodf.c,v 1.7 2008/02/22 02:30:34 das Exp $";
  18 #endif
  19
  20 /*
  21  * __ieee754_fmodf(x,y)
  22  * Return x mod y in exact arithmetic
  23  * Method: shift and subtract
  24  */
  25
  26 #include "math.h"
  27 #include "math_private.h"
  28
  29 static const float one = 1.0, Zero[] = {0.0, -0.0,};
  30
  31 float
  32 __ieee754_fmodf(float x, float y)
  33 {
  34         int32_t n,hx,hy,hz,ix,iy,sx,i;
  35
  36         GET_FLOAT_WORD(hx,x);
  37         GET_FLOAT_WORD(hy,y);
  38         sx = hx&0x80000000;             /* sign of x */
  39         hx ^=sx;                /* |x| */
  40         hy &= 0x7fffffff;       /* |y| */
  41
  42     /* purge off exception values */
  43         if(hy==0||(hx>=0x7f800000)||            /* y=0,or x not finite */
  44            (hy>0x7f800000))                     /* or y is NaN */
  45             return (x*y)/(x*y);
  46         if(hx<hy) return x;                     /* |x|<|y| return x */
  47         if(hx==hy)
  48             return Zero[(uint32_t)sx>>31];      /* |x|=|y| return x*0*/
  49
  50     /* determine ix = ilogb(x) */
  51         if(hx<0x00800000) {     /* subnormal x */
  52             for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
  53         } else ix = (hx>>23)-127;
  54
  55     /* determine iy = ilogb(y) */
  56         if(hy<0x00800000) {     /* subnormal y */
  57             for (iy = -126,i=(hy<<8); i>=0; i<<=1) iy -=1;
  58         } else iy = (hy>>23)-127;
  59
  60     /* set up {hx,lx}, {hy,ly} and align y to x */
  61         if(ix >= -126)
  62             hx = 0x00800000|(0x007fffff&hx);
  63         else {          /* subnormal x, shift x to normal */
  64             n = -126-ix;
  65             hx = hx<<n;
  66         }
  67         if(iy >= -126)
  68             hy = 0x00800000|(0x007fffff&hy);
  69         else {          /* subnormal y, shift y to normal */
  70             n = -126-iy;
  71             hy = hy<<n;
  72         }
  73
  74     /* fix point fmod */
  75         n = ix - iy;
  76         while(n--) {
  77             hz=hx-hy;
  78             if(hz<0){hx = hx+hx;}
  79             else {
  80                 if(hz==0)               /* return sign(x)*0 */
  81                     return Zero[(uint32_t)sx>>31];
  82                 hx = hz+hz;
  83             }
  84         }
  85         hz=hx-hy;
  86         if(hz>=0) {hx=hz;}
  87
  88     /* convert back to floating value and restore the sign */
  89         if(hx==0)                       /* return sign(x)*0 */
  90             return Zero[(uint32_t)sx>>31];
  91         while(hx<0x00800000) {          /* normalize x */
  92             hx = hx+hx;
  93             iy -= 1;
  94         }
  95         if(iy>= -126) {         /* normalize output */
  96             hx = ((hx-0x00800000)|((iy+127)<<23));
  97             SET_FLOAT_WORD(x,hx|sx);
  98         } else {                /* subnormal output */
  99             n = -126 - iy;
 100             hx >>= n;
 101             SET_FLOAT_WORD(x,hx|sx);
 102             x *= one;           /* create necessary signal */
 103         }
 104         return x;               /* exact output */
 105 }