lib/libm/src/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  * $NetBSD: e_remainder.c,v 1.11 2002/05/26 22:01:52 wiz Exp $
  13  * $DragonFly: src/lib/libm/src/e_remainder.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  14  */
  15
  16 /* remainder(x,p)
  17  * Return :
  18  *      returns  x REM p  =  x - [x/p]*p as if in infinite
  19  *      precise arithmetic, where [x/p] is the (infinite bit)
  20  *      integer nearest x/p (in half way case choose the even one).
  21  * Method :
  22  *      Based on fmod() return x-[x/p]chopped*p exactlp.
  23  */
  24
  25 #include <math.h>
  26 #include "math_private.h"
  27
  28 static const double zero = 0.0;
  29
  30
  31 double
  32 remainder(double x, double p)
  33 {
  34         int32_t hx,hp;
  35         u_int32_t sx,lx,lp;
  36         double p_half;
  37
  38         EXTRACT_WORDS(hx,lx,x);
  39         EXTRACT_WORDS(hp,lp,p);
  40         sx = hx&0x80000000;
  41         hp &= 0x7fffffff;
  42         hx &= 0x7fffffff;
  43
  44     /* purge off exception values */
  45         if((hp|lp)==0) return (x*p)/(x*p);      /* p = 0 */
  46         if((hx>=0x7ff00000)||                   /* x not finite */
  47           ((hp>=0x7ff00000)&&                   /* p is NaN */
  48           (((hp-0x7ff00000)|lp)!=0)))
  49             return (x*p)/(x*p);
  50
  51
  52         if (hp<=0x7fdfffff) x = fmod(x,p+p);    /* now x < 2p */
  53         if (((hx-hp)|(lx-lp))==0) return zero*x;
  54         x  = fabs(x);
  55         p  = fabs(p);
  56         if (hp<0x00200000) {
  57             if(x+x>p) {
  58                 x-=p;
  59                 if(x+x>=p) x -= p;
  60             }
  61         } else {
  62             p_half = 0.5*p;
  63             if(x>p_half) {
  64                 x-=p;
  65                 if(x>=p_half) x -= p;
  66             }
  67         }
  68         GET_HIGH_WORD(hx,x);
  69         SET_HIGH_WORD(x,hx^sx);
  70         return x;
  71 }