js/src/fdlibm/e_fmod.c

   1 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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  14  * License.
  15  *
  16  * The Original Code is Mozilla Communicator client code, released
  17  * March 31, 1998.
  18  *
  19  * The Initial Developer of the Original Code is
  20  * Sun Microsystems, Inc.
  21  * Portions created by the Initial Developer are Copyright (C) 1998
  22  * the Initial Developer. All Rights Reserved.
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  39
  40 /* @(#)e_fmod.c 1.3 95/01/18 */
  41 /*
  42  * ====================================================
  43  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  44  *
  45  * Developed at SunSoft, a Sun Microsystems, Inc. business.
  46  * Permission to use, copy, modify, and distribute this
  47  * software is freely granted, provided that this notice
  48  * is preserved.
  49  * ====================================================
  50  */
  51
  52 /*
  53  * __ieee754_fmod(x,y)
  54  * Return x mod y in exact arithmetic
  55  * Method: shift and subtract
  56  */
  57
  58 #include "fdlibm.h"
  59
  60 #ifdef __STDC__
  61 static const double one = 1.0, Zero[] = {0.0, -0.0,};
  62 #else
  63 static double one = 1.0, Zero[] = {0.0, -0.0,};
  64 #endif
  65
  66 #ifdef __STDC__
  67         double __ieee754_fmod(double x, double y)
  68 #else
  69         double __ieee754_fmod(x,y)
  70         double x,y ;
  71 #endif
  72 {
  73         fd_twoints ux, uy;
  74         int n,hx,hy,hz,ix,iy,sx,i;
  75         unsigned lx,ly,lz;
  76
  77         ux.d = x; uy.d = y;
  78         hx = __HI(ux);          /* high word of x */
  79         lx = __LO(ux);          /* low  word of x */
  80         hy = __HI(uy);          /* high word of y */
  81         ly = __LO(uy);          /* low  word of y */
  82         sx = hx&0x80000000;             /* sign of x */
  83         hx ^=sx;                /* |x| */
  84         hy &= 0x7fffffff;       /* |y| */
  85
  86     /* purge off exception values */
  87         if((hy|ly)==0||(hx>=0x7ff00000)||       /* y=0,or x not finite */
  88           ((hy|((ly|-(int)ly)>>31))>0x7ff00000))        /* or y is NaN */
  89             return (x*y)/(x*y);
  90         if(hx<=hy) {
  91             if((hx<hy)||(lx<ly)) return x;      /* |x|<|y| return x */
  92             if(lx==ly)
  93                 return Zero[(unsigned)sx>>31];  /* |x|=|y| return x*0*/
  94         }
  95
  96     /* determine ix = ilogb(x) */
  97         if(hx<0x00100000) {     /* subnormal x */
  98             if(hx==0) {
  99                 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
 100             } else {
 101                 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
 102             }
 103         } else ix = (hx>>20)-1023;
 104
 105     /* determine iy = ilogb(y) */
 106         if(hy<0x00100000) {     /* subnormal y */
 107             if(hy==0) {
 108                 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
 109             } else {
 110                 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
 111             }
 112         } else iy = (hy>>20)-1023;
 113
 114     /* set up {hx,lx}, {hy,ly} and align y to x */
 115         if(ix >= -1022)
 116             hx = 0x00100000|(0x000fffff&hx);
 117         else {          /* subnormal x, shift x to normal */
 118             n = -1022-ix;
 119             if(n<=31) {
 120                 hx = (hx<<n)|(lx>>(32-n));
 121                 lx <<= n;
 122             } else {
 123                 hx = lx<<(n-32);
 124                 lx = 0;
 125             }
 126         }
 127         if(iy >= -1022)
 128             hy = 0x00100000|(0x000fffff&hy);
 129         else {          /* subnormal y, shift y to normal */
 130             n = -1022-iy;
 131             if(n<=31) {
 132                 hy = (hy<<n)|(ly>>(32-n));
 133                 ly <<= n;
 134             } else {
 135                 hy = ly<<(n-32);
 136                 ly = 0;
 137             }
 138         }
 139
 140     /* fix point fmod */
 141         n = ix - iy;
 142         while(n--) {
 143             hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
 144             if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
 145             else {
 146                 if((hz|lz)==0)          /* return sign(x)*0 */
 147                     return Zero[(unsigned)sx>>31];
 148                 hx = hz+hz+(lz>>31); lx = lz+lz;
 149             }
 150         }
 151         hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
 152         if(hz>=0) {hx=hz;lx=lz;}
 153
 154     /* convert back to floating value and restore the sign */
 155         if((hx|lx)==0)                  /* return sign(x)*0 */
 156             return Zero[(unsigned)sx>>31];
 157         while(hx<0x00100000) {          /* normalize x */
 158             hx = hx+hx+(lx>>31); lx = lx+lx;
 159             iy -= 1;
 160         }
 161         if(iy>= -1022) {        /* normalize output */
 162             hx = ((hx-0x00100000)|((iy+1023)<<20));
 163             ux.d = x;
 164             __HI(ux) = hx|sx;
 165             __LO(ux) = lx;
 166             x = ux.d;
 167         } else {                /* subnormal output */
 168             n = -1022 - iy;
 169             if(n<=20) {
 170                 lx = (lx>>n)|((unsigned)hx<<(32-n));
 171                 hx >>= n;
 172             } else if (n<=31) {
 173                 lx = (hx<<(32-n))|(lx>>n); hx = sx;
 174             } else {
 175                 lx = hx>>(n-32); hx = sx;
 176             }
 177             ux.d = x;
 178             __HI(ux) = hx|sx;
 179             __LO(ux) = lx;
 180             x = ux.d;
 181             x *= one;           /* create necessary signal */
 182         }
 183         return x;               /* exact output */
 184 }