newlib/libm/mathfp/e_remainder.c

   1
   2 /* @(#)e_remainder.c 5.1 93/09/24 */
   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 <<remainder>>, <<remainderf>>---round and  remainder
  17 INDEX
  18         remainder
  19 INDEX
  20         remainderf
  21
  22 SYNOPSIS
  23         #include <math.h>
  24         double remainder(double <[x]>, double <[y]>);
  25         float remainderf(float <[x]>, float <[y]>);
  26
  27 DESCRIPTION
  28 <<remainder>> and <<remainderf>> find the remainder of
  29 <[x]>/<[y]>; this value is in the range -<[y]>/2 .. +<[y]>/2.
  30
  31 RETURNS
  32 <<remainder>> returns the integer result as a double.
  33
  34 PORTABILITY
  35 <<remainder>> is a System V release 4.
  36 <<remainderf>> is an extension.
  37
  38 */
  39
  40 /* remainder(x,p)
  41  * Return :
  42  *      returns  x REM p  =  x - [x/p]*p as if in infinite
  43  *      precise arithmetic, where [x/p] is the (infinite bit)
  44  *      integer nearest x/p (in half way case choose the even one).
  45  * Method :
  46  *      Based on fmod() return x-[x/p]chopped*p exactlp.
  47  */
  48
  49 #include "fdlibm.h"
  50
  51 #ifndef _DOUBLE_IS_32BITS
  52
  53 #ifdef __STDC__
  54 static const double zero = 0.0;
  55 #else
  56 static double zero = 0.0;
  57 #endif
  58
  59
  60 #ifdef __STDC__
  61         double remainder(double x, double p)
  62 #else
  63         double remainder(x,p)
  64         double x,p;
  65 #endif
  66 {
  67         __int32_t hx,hp;
  68         __uint32_t sx,lx,lp;
  69         double p_half;
  70
  71         EXTRACT_WORDS(hx,lx,x);
  72         EXTRACT_WORDS(hp,lp,p);
  73         sx = hx&0x80000000;
  74         hp &= 0x7fffffff;
  75         hx &= 0x7fffffff;
  76
  77     /* purge off exception values */
  78         if((hp|lp)==0) return (x*p)/(x*p);      /* p = 0 */
  79         if((hx>=0x7ff00000)||                   /* x not finite */
  80           ((hp>=0x7ff00000)&&                   /* p is NaN */
  81           (((hp-0x7ff00000)|lp)!=0)))
  82             return (x*p)/(x*p);
  83
  84
  85         if (hp<=0x7fdfffff) x = fmod(x,p+p);    /* now x < 2p */
  86         if (((hx-hp)|(lx-lp))==0) return zero*x;
  87         x  = fabs(x);
  88         p  = fabs(p);
  89         if (hp<0x00200000) {
  90             if(x+x>p) {
  91                 x-=p;
  92                 if(x+x>=p) x -= p;
  93             }
  94         } else {
  95             p_half = 0.5*p;
  96             if(x>p_half) {
  97                 x-=p;
  98                 if(x>=p_half) x -= p;
  99             }
 100         }
 101         GET_HIGH_WORD(hx,x);
 102         SET_HIGH_WORD(x,hx^sx);
 103         return x;
 104 }
 105
 106 #endif /* defined(_DOUBLE_IS_32BITS) */