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
  16 #include <sys/cdefs.h>
  17 #if defined(LIBM_SCCS) && !defined(lint)
  18 __RCSID("$NetBSD: e_fmodf.c,v 1.7 2002/05/26 22:01:49 wiz Exp $");
  19 #endif
  20
  21 /*
  22  * __ieee754_fmodf(x,y)
  23  * Return x mod y in exact arithmetic
  24  * Method: shift and subtract
  25  */
  26
  27 #include "math.h"
  28 #include "math_private.h"
  29
  30 static const float one = 1.0, Zero[] = {0.0, -0.0,};
  31
  32 float
  33 __ieee754_fmodf(float x, float y)
  34 {
  35         int32_t n,hx,hy,hz,ix,iy,sx,i;
  36
  37         GET_FLOAT_WORD(hx,x);
  38         GET_FLOAT_WORD(hy,y);
  39         sx = hx&0x80000000;             /* sign of x */
  40         hx ^=sx;                /* |x| */
  41         hy &= 0x7fffffff;       /* |y| */
  42
  43     /* purge off exception values */
  44         if(hy==0||(hx>=0x7f800000)||            /* y=0,or x not finite */
  45            (hy>0x7f800000))                     /* or y is NaN */
  46             return (x*y)/(x*y);
  47         if(hx<hy) return x;                     /* |x|<|y| return x */
  48         if(hx==hy)
  49             return Zero[(u_int32_t)sx>>31];     /* |x|=|y| return x*0*/
  50
  51     /* determine ix = ilogb(x) */
  52         if(hx<0x00800000) {     /* subnormal x */
  53             for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
  54         } else ix = (hx>>23)-127;
  55
  56     /* determine iy = ilogb(y) */
  57         if(hy<0x00800000) {     /* subnormal y */
  58             for (iy = -126,i=(hy<<8); i>=0; i<<=1) iy -=1;
  59         } else iy = (hy>>23)-127;
  60
  61     /* set up {hx,lx}, {hy,ly} and align y to x */
  62         if(ix >= -126)
  63             hx = 0x00800000|(0x007fffff&hx);
  64         else {          /* subnormal x, shift x to normal */
  65             n = -126-ix;
  66             hx = hx<<n;
  67         }
  68         if(iy >= -126)
  69             hy = 0x00800000|(0x007fffff&hy);
  70         else {          /* subnormal y, shift y to normal */
  71             n = -126-iy;
  72             hy = hy<<n;
  73         }
  74
  75     /* fix point fmod */
  76         n = ix - iy;
  77         while(n--) {
  78             hz=hx-hy;
  79             if(hz<0){hx = hx+hx;}
  80             else {
  81                 if(hz==0)               /* return sign(x)*0 */
  82                     return Zero[(u_int32_t)sx>>31];
  83                 hx = hz+hz;
  84             }
  85         }
  86         hz=hx-hy;
  87         if(hz>=0) {hx=hz;}
  88
  89     /* convert back to floating value and restore the sign */
  90         if(hx==0)                       /* return sign(x)*0 */
  91             return Zero[(u_int32_t)sx>>31];
  92         while(hx<0x00800000) {          /* normalize x */
  93             hx = hx+hx;
  94             iy -= 1;
  95         }
  96         if(iy>= -126) {         /* normalize output */
  97             hx = ((hx-0x00800000)|((iy+127)<<23));
  98             SET_FLOAT_WORD(x,hx|sx);
  99         } else {                /* subnormal output */
 100             n = -126 - iy;
 101             hx >>= n;
 102             SET_FLOAT_WORD(x,hx|sx);
 103             x *= one;           /* create necessary signal */
 104         }
 105         return x;               /* exact output */
 106 }