StdLib/LibC/Math/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 #include  <LibConfig.h>
  13 #include  <sys/EfiCdefs.h>
  14 #if defined(LIBM_SCCS) && !defined(lint)
  15 __RCSID("$NetBSD: e_fmod.c,v 1.11 2002/05/26 22:01:49 wiz Exp $");
  16 #endif
  17
  18 /*
  19  * __ieee754_fmod(x,y)
  20  * Return x mod y in exact arithmetic
  21  * Method: shift and subtract
  22  */
  23
  24 #include "math.h"
  25 #include "math_private.h"
  26
  27 #if defined(_MSC_VER)           /* Handle Microsoft VC++ compiler specifics. */
  28   // unary minus operator applied to unsigned type, result still unsigned
  29   #pragma warning ( disable : 4146 )
  30 #endif
  31
  32 static const double one = 1.0, Zero[] = {0.0, -0.0,};
  33
  34 double
  35 __ieee754_fmod(double x, double y)
  36 {
  37   int32_t n,hx,hy,hz,ix,iy,sx,i;
  38   u_int32_t lx,ly,lz;
  39
  40   EXTRACT_WORDS(hx,lx,x);
  41   EXTRACT_WORDS(hy,ly,y);
  42   sx = hx&0x80000000;   /* sign of x */
  43   hx ^=sx;    /* |x| */
  44   hy &= 0x7fffffff; /* |y| */
  45
  46     /* purge off exception values */
  47   if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */
  48     ((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */
  49       return (x*y)/(x*y);
  50   if(hx<=hy) {
  51       if((hx<hy)||(lx<ly)) return x;  /* |x|<|y| return x */
  52       if(lx==ly)
  53     return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
  54   }
  55
  56     /* determine ix = ilogb(x) */
  57   if(hx<0x00100000) { /* subnormal x */
  58       if(hx==0) {
  59     for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
  60       } else {
  61     for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
  62       }
  63   } else ix = (hx>>20)-1023;
  64
  65     /* determine iy = ilogb(y) */
  66   if(hy<0x00100000) { /* subnormal y */
  67       if(hy==0) {
  68     for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
  69       } else {
  70     for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
  71       }
  72   } else iy = (hy>>20)-1023;
  73
  74     /* set up {hx,lx}, {hy,ly} and align y to x */
  75   if(ix >= -1022)
  76       hx = 0x00100000|(0x000fffff&hx);
  77   else {    /* subnormal x, shift x to normal */
  78       n = -1022-ix;
  79       if(n<=31) {
  80           hx = (hx<<n)|(lx>>(32-n));
  81           lx <<= n;
  82       } else {
  83     hx = lx<<(n-32);
  84     lx = 0;
  85       }
  86   }
  87   if(iy >= -1022)
  88       hy = 0x00100000|(0x000fffff&hy);
  89   else {    /* subnormal y, shift y to normal */
  90       n = -1022-iy;
  91       if(n<=31) {
  92           hy = (hy<<n)|(ly>>(32-n));
  93           ly <<= n;
  94       } else {
  95     hy = ly<<(n-32);
  96     ly = 0;
  97       }
  98   }
  99
 100     /* fix point fmod */
 101   n = ix - iy;
 102   while(n--) {
 103       hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
 104       if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
 105       else {
 106         if((hz|lz)==0)    /* return sign(x)*0 */
 107         return Zero[(u_int32_t)sx>>31];
 108         hx = hz+hz+(lz>>31); lx = lz+lz;
 109       }
 110   }
 111   hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
 112   if(hz>=0) {hx=hz;lx=lz;}
 113
 114     /* convert back to floating value and restore the sign */
 115   if((hx|lx)==0)      /* return sign(x)*0 */
 116       return Zero[(u_int32_t)sx>>31];
 117   while(hx<0x00100000) {    /* normalize x */
 118       hx = hx+hx+(lx>>31); lx = lx+lx;
 119       iy -= 1;
 120   }
 121   if(iy>= -1022) {  /* normalize output */
 122       hx = ((hx-0x00100000)|((iy+1023)<<20));
 123       INSERT_WORDS(x,hx|sx,lx);
 124   } else {    /* subnormal output */
 125       n = -1022 - iy;
 126       if(n<=20) {
 127     lx = (lx>>n)|((u_int32_t)hx<<(32-n));
 128     hx >>= n;
 129       } else if (n<=31) {
 130     lx = (hx<<(32-n))|(lx>>n); hx = sx;
 131       } else {
 132     lx = hx>>(n-32); hx = sx;
 133       }
 134       INSERT_WORDS(x,hx|sx,lx);
 135       x *= one;   /* create necessary signal */
 136   }
 137   return x;   /* exact output */
 138 }