lib/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  * $NetBSD: e_fmodf.c,v 1.7 2002/05/26 22:01:49 wiz Exp $
  16  * $DragonFly: src/lib/libm/src/e_fmodf.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  17  */
  18
  19 /*
  20  * fmodf(x,y)
  21  * Return x mod y in exact arithmetic
  22  * Method: shift and subtract
  23  */
  24
  25 #include <math.h>
  26 #include "math_private.h"
  27
  28 static const float one = 1.0, Zero[] = {0.0, -0.0,};
  29
  30 float
  31 fmodf(float x, float y)
  32 {
  33         int32_t n,hx,hy,hz,ix,iy,sx,i;
  34
  35         GET_FLOAT_WORD(hx,x);
  36         GET_FLOAT_WORD(hy,y);
  37         sx = hx&0x80000000;             /* sign of x */
  38         hx ^=sx;                /* |x| */
  39         hy &= 0x7fffffff;       /* |y| */
  40
  41     /* purge off exception values */
  42         if(hy==0||(hx>=0x7f800000)||            /* y=0,or x not finite */
  43            (hy>0x7f800000))                     /* or y is NaN */
  44             return (x*y)/(x*y);
  45         if(hx<hy) return x;                     /* |x|<|y| return x */
  46         if(hx==hy)
  47             return Zero[(u_int32_t)sx>>31];     /* |x|=|y| return x*0*/
  48
  49     /* determine ix = ilogb(x) */
  50         if(hx<0x00800000) {     /* subnormal x */
  51             for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
  52         } else ix = (hx>>23)-127;
  53
  54     /* determine iy = ilogb(y) */
  55         if(hy<0x00800000) {     /* subnormal y */
  56             for (iy = -126,i=(hy<<8); i>=0; i<<=1) iy -=1;
  57         } else iy = (hy>>23)-127;
  58
  59     /* set up {hx,lx}, {hy,ly} and align y to x */
  60         if(ix >= -126)
  61             hx = 0x00800000|(0x007fffff&hx);
  62         else {          /* subnormal x, shift x to normal */
  63             n = -126-ix;
  64             hx = hx<<n;
  65         }
  66         if(iy >= -126)
  67             hy = 0x00800000|(0x007fffff&hy);
  68         else {          /* subnormal y, shift y to normal */
  69             n = -126-iy;
  70             hy = hy<<n;
  71         }
  72
  73     /* fix point fmod */
  74         n = ix - iy;
  75         while(n--) {
  76             hz=hx-hy;
  77             if(hz<0){hx = hx+hx;}
  78             else {
  79                 if(hz==0)               /* return sign(x)*0 */
  80                     return Zero[(u_int32_t)sx>>31];
  81                 hx = hz+hz;
  82             }
  83         }
  84         hz=hx-hy;
  85         if(hz>=0) {hx=hz;}
  86
  87     /* convert back to floating value and restore the sign */
  88         if(hx==0)                       /* return sign(x)*0 */
  89             return Zero[(u_int32_t)sx>>31];
  90         while(hx<0x00800000) {          /* normalize x */
  91             hx = hx+hx;
  92             iy -= 1;
  93         }
  94         if(iy>= -126) {         /* normalize output */
  95             hx = ((hx-0x00800000)|((iy+127)<<23));
  96             SET_FLOAT_WORD(x,hx|sx);
  97         } else {                /* subnormal output */
  98             n = -126 - iy;
  99             hx >>= n;
 100             SET_FLOAT_WORD(x,hx|sx);
 101             x *= one;           /* create necessary signal */
 102         }
 103         return x;               /* exact output */
 104 }