e_remainder.c (1713B)
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 #ifndef lint 14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_remainder.c,v 1.9 2003/07/23 04:53:46 peter 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 static const double zero = 0.0; 30 31 32 double 33 __ieee754_remainder(double x, double p) 34 { 35 int32_t hx,hp; 36 u_int32_t sx,lx,lp; 37 double p_half; 38 39 EXTRACT_WORDS(hx,lx,x); 40 EXTRACT_WORDS(hp,lp,p); 41 sx = hx&0x80000000; 42 hp &= 0x7fffffff; 43 hx &= 0x7fffffff; 44 45 /* purge off exception values */ 46 if((hp|lp)==0) return (x*p)/(x*p); /* p = 0 */ 47 if((hx>=0x7ff00000)|| /* x not finite */ 48 ((hp>=0x7ff00000)&& /* p is NaN */ 49 (((hp-0x7ff00000)|lp)!=0))) 50 return (x*p)/(x*p); 51 52 53 if (hp<=0x7fdfffff) x = __ieee754_fmod(x,p+p); /* now x < 2p */ 54 if (((hx-hp)|(lx-lp))==0) return zero*x; 55 x = fabs(x); 56 p = fabs(p); 57 if (hp<0x00200000) { 58 if(x+x>p) { 59 x-=p; 60 if(x+x>=p) x -= p; 61 } 62 } else { 63 p_half = 0.5*p; 64 if(x>p_half) { 65 x-=p; 66 if(x>=p_half) x -= p; 67 } 68 } 69 GET_HIGH_WORD(hx,x); 70 SET_HIGH_WORD(x,hx^sx); 71 return x; 72 }