libm/e_remainder.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /* __ieee754_remainder(x,p)
  13  * Return :
  14  *      returns  x REM p  =  x - [x/p]*p as if in infinite
  15  *      precise arithmetic, where [x/p] is the (infinite bit)
  16  *      integer nearest x/p (in half way case choose the even one).
  17  * Method :
  18  *      Based on fmod() return x-[x/p]chopped*p exactlp.
  19  */
  20
  21 #include "math.h"
  22 #include "math_private.h"
  23
  24 static const double zero = 0.0;
  25
  26 double __ieee754_remainder(double x, double p)
  27 {
  28         int32_t hx,hp;
  29         u_int32_t sx,lx,lp;
  30         double p_half;
  31
  32         EXTRACT_WORDS(hx,lx,x);
  33         EXTRACT_WORDS(hp,lp,p);
  34         sx = hx&0x80000000;
  35         hp &= 0x7fffffff;
  36         hx &= 0x7fffffff;
  37
  38     /* purge off exception values */
  39         if((hp|lp)==0) return (x*p)/(x*p);      /* p = 0 */
  40         if((hx>=0x7ff00000)||                   /* x not finite */
  41           ((hp>=0x7ff00000)&&                   /* p is NaN */
  42           (((hp-0x7ff00000)|lp)!=0)))
  43             return (x*p)/(x*p);
  44
  45
  46         if (hp<=0x7fdfffff) x = __ieee754_fmod(x,p+p);  /* now x < 2p */
  47         if (((hx-hp)|(lx-lp))==0) return zero*x;
  48         x  = fabs(x);
  49         p  = fabs(p);
  50         if (hp<0x00200000) {
  51             if(x+x>p) {
  52                 x-=p;
  53                 if(x+x>=p) x -= p;
  54             }
  55         } else {
  56             p_half = 0.5*p;
  57             if(x>p_half) {
  58                 x-=p;
  59                 if(x>=p_half) x -= p;
  60             }
  61         }
  62         GET_HIGH_WORD(hx,x);
  63         SET_HIGH_WORD(x,hx^sx);
  64         return x;
  65 }
  66
  67 strong_alias(__ieee754_remainder, remainder)
  68 strong_alias(__ieee754_remainder, drem)
  69 libm_hidden_def(remainder)