sysdeps/libm-ieee754/e_fmod.c

   1 /* @(#)e_fmod.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 #if defined(LIBM_SCCS) && !defined(lint)
  14 static char rcsid[] = "$NetBSD: e_fmod.c,v 1.8 1995/05/10 20:45:07 jtc Exp $";
  15 #endif
  16
  17 /*
  18  * __ieee754_fmod(x,y)
  19  * Return x mod y in exact arithmetic
  20  * Method: shift and subtract
  21  */
  22
  23 #include "math.h"
  24 #include "math_private.h"
  25
  26 #ifdef __STDC__
  27 static const double one = 1.0, Zero[] = {0.0, -0.0,};
  28 #else
  29 static double one = 1.0, Zero[] = {0.0, -0.0,};
  30 #endif
  31
  32 #ifdef __STDC__
  33         double __ieee754_fmod(double x, double y)
  34 #else
  35         double __ieee754_fmod(x,y)
  36         double x,y ;
  37 #endif
  38 {
  39         int32_t n,hx,hy,hz,ix,iy,sx,i;
  40         u_int32_t lx,ly,lz;
  41
  42         EXTRACT_WORDS(hx,lx,x);
  43         EXTRACT_WORDS(hy,ly,y);
  44         sx = hx&0x80000000;             /* sign of x */
  45         hx ^=sx;                /* |x| */
  46         hy &= 0x7fffffff;       /* |y| */
  47
  48     /* purge off exception values */
  49         if((hy|ly)==0||(hx>=0x7ff00000)||       /* y=0,or x not finite */
  50           ((hy|((ly|-ly)>>31))>0x7ff00000))     /* or y is NaN */
  51             return (x*y)/(x*y);
  52         if(hx<=hy) {
  53             if((hx<hy)||(lx<ly)) return x;      /* |x|<|y| return x */
  54             if(lx==ly)
  55                 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
  56         }
  57
  58     /* determine ix = ilogb(x) */
  59         if(hx<0x00100000) {     /* subnormal x */
  60             if(hx==0) {
  61                 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
  62             } else {
  63                 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
  64             }
  65         } else ix = (hx>>20)-1023;
  66
  67     /* determine iy = ilogb(y) */
  68         if(hy<0x00100000) {     /* subnormal y */
  69             if(hy==0) {
  70                 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
  71             } else {
  72                 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
  73             }
  74         } else iy = (hy>>20)-1023;
  75
  76     /* set up {hx,lx}, {hy,ly} and align y to x */
  77         if(ix >= -1022)
  78             hx = 0x00100000|(0x000fffff&hx);
  79         else {          /* subnormal x, shift x to normal */
  80             n = -1022-ix;
  81             if(n<=31) {
  82                 hx = (hx<<n)|(lx>>(32-n));
  83                 lx <<= n;
  84             } else {
  85                 hx = lx<<(n-32);
  86                 lx = 0;
  87             }
  88         }
  89         if(iy >= -1022)
  90             hy = 0x00100000|(0x000fffff&hy);
  91         else {          /* subnormal y, shift y to normal */
  92             n = -1022-iy;
  93             if(n<=31) {
  94                 hy = (hy<<n)|(ly>>(32-n));
  95                 ly <<= n;
  96             } else {
  97                 hy = ly<<(n-32);
  98                 ly = 0;
  99             }
 100         }
 101
 102     /* fix point fmod */
 103         n = ix - iy;
 104         while(n--) {
 105             hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
 106             if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
 107             else {
 108                 if((hz|lz)==0)          /* return sign(x)*0 */
 109                     return Zero[(u_int32_t)sx>>31];
 110                 hx = hz+hz+(lz>>31); lx = lz+lz;
 111             }
 112         }
 113         hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
 114         if(hz>=0) {hx=hz;lx=lz;}
 115
 116     /* convert back to floating value and restore the sign */
 117         if((hx|lx)==0)                  /* return sign(x)*0 */
 118             return Zero[(u_int32_t)sx>>31];
 119         while(hx<0x00100000) {          /* normalize x */
 120             hx = hx+hx+(lx>>31); lx = lx+lx;
 121             iy -= 1;
 122         }
 123         if(iy>= -1022) {        /* normalize output */
 124             hx = ((hx-0x00100000)|((iy+1023)<<20));
 125             INSERT_WORDS(x,hx|sx,lx);
 126         } else {                /* subnormal output */
 127             n = -1022 - iy;
 128             if(n<=20) {
 129                 lx = (lx>>n)|((u_int32_t)hx<<(32-n));
 130                 hx >>= n;
 131             } else if (n<=31) {
 132                 lx = (hx<<(32-n))|(lx>>n); hx = sx;
 133             } else {
 134                 lx = hx>>(n-32); hx = sx;
 135             }
 136             INSERT_WORDS(x,hx|sx,lx);
 137             x *= one;           /* create necessary signal */
 138         }
 139         return x;               /* exact output */
 140 }