toolchain/gcc/newlib/libm/mathfp/s_fmod.c

   1
   2 /* @(#)z_fmod.c 1.0 98/08/13 */
   3 /*
   4  * ====================================================
   5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   6  *
   7  * Developed at SunPro, a Sun Microsystems, Inc. business.
   8  * Permission to use, copy, modify, and distribute this
   9  * software is freely granted, provided that this notice
  10  * is preserved.
  11  * ====================================================
  12  */
  13
  14 /*
  15 FUNCTION
  16 <<fmod>>, <<fmodf>>---floating-point remainder (modulo)
  17
  18 INDEX
  19 fmod
  20 INDEX
  21 fmodf
  22
  23 ANSI_SYNOPSIS
  24 #include <math.h>
  25 double fmod(double <[x]>, double <[y]>)
  26 float fmodf(float <[x]>, float <[y]>)
  27
  28 TRAD_SYNOPSIS
  29 #include <math.h>
  30 double fmod(<[x]>, <[y]>)
  31 double (<[x]>, <[y]>);
  32
  33 float fmodf(<[x]>, <[y]>)
  34 float (<[x]>, <[y]>);
  35
  36 DESCRIPTION
  37 The <<fmod>> and <<fmodf>> functions compute the floating-point
  38 remainder of <[x]>/<[y]> (<[x]> modulo <[y]>).
  39
  40 RETURNS
  41 The <<fmod>> function returns the value
  42 @ifnottex
  43 <[x]>-<[i]>*<[y]>,
  44 @end ifnottex
  45 @tex
  46 $x-i\times y$,
  47 @end tex
  48 for the largest integer <[i]> such that, if <[y]> is nonzero, the
  49 result has the same sign as <[x]> and magnitude less than the
  50 magnitude of <[y]>.
  51
  52 <<fmod(<[x]>,0)>> returns NaN, and sets <<errno>> to <<EDOM>>.
  53
  54 You can modify error treatment for these functions using <<matherr>>.
  55
  56 PORTABILITY
  57 <<fmod>> is ANSI C. <<fmodf>> is an extension.
  58 */
  59
  60 /*
  61  * fmod(x,y)
  62  * Return x mod y in exact arithmetic
  63  * Method: shift and subtract
  64  */
  65
  66 #include "fdlibm.h"
  67 #include "zmath.h"
  68
  69 #ifndef _DOUBLE_IS_32BITS
  70
  71 #ifdef __STDC__
  72 static const double one = 1.0, Zero[] = {0.0, -0.0,};
  73 #else
  74 static double one = 1.0, Zero[] = {0.0, -0.0,};
  75 #endif
  76
  77 #ifdef __STDC__
  78         double fmod(double x, double y)
  79 #else
  80         double fmod(x,y)
  81         double x,y ;
  82 #endif
  83 {
  84         __int32_t n,hx,hy,hz,ix,iy,sx,i;
  85         __uint32_t lx,ly,lz;
  86
  87         EXTRACT_WORDS(hx,lx,x);
  88         EXTRACT_WORDS(hy,ly,y);
  89         sx = hx&0x80000000;             /* sign of x */
  90         hx ^=sx;                /* |x| */
  91         hy &= 0x7fffffff;       /* |y| */
  92
  93     /* purge off exception values */
  94         if((hy|ly)==0||(hx>=0x7ff00000)||       /* y=0,or x not finite */
  95           ((hy|((ly|-ly)>>31))>0x7ff00000))     /* or y is NaN */
  96             return (x*y)/(x*y);
  97         if(hx<=hy) {
  98             if((hx<hy)||(lx<ly)) return x;      /* |x|<|y| return x */
  99             if(lx==ly)
 100                 return Zero[(__uint32_t)sx>>31];        /* |x|=|y| return x*0*/
 101         }
 102
 103     /* determine ix = ilogb(x) */
 104         if(hx<0x00100000) {     /* subnormal x */
 105             if(hx==0) {
 106                 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
 107             } else {
 108                 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
 109             }
 110         } else ix = (hx>>20)-1023;
 111
 112     /* determine iy = ilogb(y) */
 113         if(hy<0x00100000) {     /* subnormal y */
 114             if(hy==0) {
 115                 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
 116             } else {
 117                 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
 118             }
 119         } else iy = (hy>>20)-1023;
 120
 121     /* set up {hx,lx}, {hy,ly} and align y to x */
 122         if(ix >= -1022)
 123             hx = 0x00100000|(0x000fffff&hx);
 124         else {          /* subnormal x, shift x to normal */
 125             n = -1022-ix;
 126             if(n<=31) {
 127                 hx = (hx<<n)|(lx>>(32-n));
 128                 lx <<= n;
 129             } else {
 130                 hx = lx<<(n-32);
 131                 lx = 0;
 132             }
 133         }
 134         if(iy >= -1022)
 135             hy = 0x00100000|(0x000fffff&hy);
 136         else {          /* subnormal y, shift y to normal */
 137             n = -1022-iy;
 138             if(n<=31) {
 139                 hy = (hy<<n)|(ly>>(32-n));
 140                 ly <<= n;
 141             } else {
 142                 hy = ly<<(n-32);
 143                 ly = 0;
 144             }
 145         }
 146
 147     /* fix point fmod */
 148         n = ix - iy;
 149         while(n--) {
 150             hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
 151             if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
 152             else {
 153                 if((hz|lz)==0)          /* return sign(x)*0 */
 154                     return Zero[(__uint32_t)sx>>31];
 155                 hx = hz+hz+(lz>>31); lx = lz+lz;
 156             }
 157         }
 158         hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
 159         if(hz>=0) {hx=hz;lx=lz;}
 160
 161     /* convert back to floating value and restore the sign */
 162         if((hx|lx)==0)                  /* return sign(x)*0 */
 163             return Zero[(__uint32_t)sx>>31];
 164         while(hx<0x00100000) {          /* normalize x */
 165             hx = hx+hx+(lx>>31); lx = lx+lx;
 166             iy -= 1;
 167         }
 168         if(iy>= -1022) {        /* normalize output */
 169             hx = ((hx-0x00100000)|((iy+1023)<<20));
 170             INSERT_WORDS(x,hx|sx,lx);
 171         } else {                /* subnormal output */
 172             n = -1022 - iy;
 173             if(n<=20) {
 174                 lx = (lx>>n)|((__uint32_t)hx<<(32-n));
 175                 hx >>= n;
 176             } else if (n<=31) {
 177                 lx = (hx<<(32-n))|(lx>>n); hx = sx;
 178             } else {
 179                 lx = hx>>(n-32); hx = sx;
 180             }
 181             INSERT_WORDS(x,hx|sx,lx);
 182             x *= one;           /* create necessary signal */
 183         }
 184         return x;               /* exact output */
 185 }
 186
 187 #endif /* defined(_DOUBLE_IS_32BITS) */