sysdeps/libm-ieee754/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 #if defined(LIBM_SCCS) && !defined(lint)
  17 static char rcsid[] = "$NetBSD: e_fmodf.c,v 1.4 1995/05/10 20:45:10 jtc 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 #ifdef __STDC__
  30 static const float one = 1.0, Zero[] = {0.0, -0.0,};
  31 #else
  32 static float one = 1.0, Zero[] = {0.0, -0.0,};
  33 #endif
  34
  35 #ifdef __STDC__
  36         float __ieee754_fmodf(float x, float y)
  37 #else
  38         float __ieee754_fmodf(x,y)
  39         float x,y ;
  40 #endif
  41 {
  42         int32_t n,hx,hy,hz,ix,iy,sx,i;
  43
  44         GET_FLOAT_WORD(hx,x);
  45         GET_FLOAT_WORD(hy,y);
  46         sx = hx&0x80000000;             /* sign of x */
  47         hx ^=sx;                /* |x| */
  48         hy &= 0x7fffffff;       /* |y| */
  49
  50     /* purge off exception values */
  51         if(hy==0||(hx>=0x7f800000)||            /* y=0,or x not finite */
  52            (hy>0x7f800000))                     /* or y is NaN */
  53             return (x*y)/(x*y);
  54         if(hx<hy) return x;                     /* |x|<|y| return x */
  55         if(hx==hy)
  56             return Zero[(u_int32_t)sx>>31];     /* |x|=|y| return x*0*/
  57
  58     /* determine ix = ilogb(x) */
  59         if(hx<0x00800000) {     /* subnormal x */
  60             for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
  61         } else ix = (hx>>23)-127;
  62
  63     /* determine iy = ilogb(y) */
  64         if(hy<0x00800000) {     /* subnormal y */
  65             for (iy = -126,i=(hy<<8); i>=0; i<<=1) iy -=1;
  66         } else iy = (hy>>23)-127;
  67
  68     /* set up {hx,lx}, {hy,ly} and align y to x */
  69         if(ix >= -126)
  70             hx = 0x00800000|(0x007fffff&hx);
  71         else {          /* subnormal x, shift x to normal */
  72             n = -126-ix;
  73             hx = hx<<n;
  74         }
  75         if(iy >= -126)
  76             hy = 0x00800000|(0x007fffff&hy);
  77         else {          /* subnormal y, shift y to normal */
  78             n = -126-iy;
  79             hy = hy<<n;
  80         }
  81
  82     /* fix point fmod */
  83         n = ix - iy;
  84         while(n--) {
  85             hz=hx-hy;
  86             if(hz<0){hx = hx+hx;}
  87             else {
  88                 if(hz==0)               /* return sign(x)*0 */
  89                     return Zero[(u_int32_t)sx>>31];
  90                 hx = hz+hz;
  91             }
  92         }
  93         hz=hx-hy;
  94         if(hz>=0) {hx=hz;}
  95
  96     /* convert back to floating value and restore the sign */
  97         if(hx==0)                       /* return sign(x)*0 */
  98             return Zero[(u_int32_t)sx>>31];
  99         while(hx<0x00800000) {          /* normalize x */
 100             hx = hx+hx;
 101             iy -= 1;
 102         }
 103         if(iy>= -126) {         /* normalize output */
 104             hx = ((hx-0x00800000)|((iy+127)<<23));
 105             SET_FLOAT_WORD(x,hx|sx);
 106         } else {                /* subnormal output */
 107             n = -126 - iy;
 108             hx >>= n;
 109             SET_FLOAT_WORD(x,hx|sx);
 110             x *= one;           /* create necessary signal */
 111         }
 112         return x;               /* exact output */
 113 }