sysdeps/libm-ieee754/e_remainder.c

   1 /* @(#)e_remainder.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_remainder.c,v 1.8 1995/05/10 20:46:05 jtc Exp $";
  15 #endif
  16
  17 /* __ieee754_remainder(x,p)
  18  * Return :
  19  *      returns  x REM p  =  x - [x/p]*p as if in infinite
  20  *      precise arithmetic, where [x/p] is the (infinite bit)
  21  *      integer nearest x/p (in half way case choose the even one).
  22  * Method :
  23  *      Based on fmod() return x-[x/p]chopped*p exactlp.
  24  */
  25
  26 #include "math.h"
  27 #include "math_private.h"
  28
  29 #ifdef __STDC__
  30 static const double zero = 0.0;
  31 #else
  32 static double zero = 0.0;
  33 #endif
  34
  35
  36 #ifdef __STDC__
  37         double __ieee754_remainder(double x, double p)
  38 #else
  39         double __ieee754_remainder(x,p)
  40         double x,p;
  41 #endif
  42 {
  43         int32_t hx,hp;
  44         u_int32_t sx,lx,lp;
  45         double p_half;
  46
  47         EXTRACT_WORDS(hx,lx,x);
  48         EXTRACT_WORDS(hp,lp,p);
  49         sx = hx&0x80000000;
  50         hp &= 0x7fffffff;
  51         hx &= 0x7fffffff;
  52
  53     /* purge off exception values */
  54         if((hp|lp)==0) return (x*p)/(x*p);      /* p = 0 */
  55         if((hx>=0x7ff00000)||                   /* x not finite */
  56           ((hp>=0x7ff00000)&&                   /* p is NaN */
  57           (((hp-0x7ff00000)|lp)!=0)))
  58             return (x*p)/(x*p);
  59
  60
  61         if (hp<=0x7fdfffff) x = __ieee754_fmod(x,p+p);  /* now x < 2p */
  62         if (((hx-hp)|(lx-lp))==0) return zero*x;
  63         x  = fabs(x);
  64         p  = fabs(p);
  65         if (hp<0x00200000) {
  66             if(x+x>p) {
  67                 x-=p;
  68                 if(x+x>=p) x -= p;
  69             }
  70         } else {
  71             p_half = 0.5*p;
  72             if(x>p_half) {
  73                 x-=p;
  74                 if(x>=p_half) x -= p;
  75             }
  76         }
  77         GET_HIGH_WORD(hx,x);
  78         SET_HIGH_WORD(x,hx^sx);
  79         return x;
  80 }