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 #include <sys/cdefs.h> 14 #if defined(LIBM_SCCS) && !defined(lint) 15 __RCSID("$NetBSD: e_remainder.c,v 1.11 2002/05/26 22:01:52 wiz Exp $"); 16 #endif 17 18 /* __ieee754_remainder(x,p) 19 * Return : 20 * returns x REM p = x - [x/p]*p as if in infinite 21 * precise arithmetic, where [x/p] is the (infinite bit) 22 * integer nearest x/p (in half way case choose the even one). 23 * Method : 24 * Based on fmod() return x-[x/p]chopped*p exactlp. 25 */ 26 27 #include "math.h" 28 #include "math_private.h" 29 30 static const double zero = 0.0; 31 32 33 double 34 __ieee754_remainder(double x, double p) 35 { 36 int32_t hx,hp; 37 u_int32_t sx,lx,lp; 38 double p_half; 39 40 EXTRACT_WORDS(hx,lx,x); 41 EXTRACT_WORDS(hp,lp,p); 42 sx = hx&0x80000000; 43 hp &= 0x7fffffff; 44 hx &= 0x7fffffff; 45 46 /* purge off exception values */ 47 if((hp|lp)==0) return (x*p)/(x*p); /* p = 0 */ 48 if((hx>=0x7ff00000)|| /* x not finite */ 49 ((hp>=0x7ff00000)&& /* p is NaN */ 50 (((hp-0x7ff00000)|lp)!=0))) 51 return (x*p)/(x*p); 52 53 54 if (hp<=0x7fdfffff) x = __ieee754_fmod(x,p+p); /* now x < 2p */ 55 if (((hx-hp)|(lx-lp))==0) return zero*x; 56 x = fabs(x); 57 p = fabs(p); 58 if (hp<0x00200000) { 59 if(x+x>p) { 60 x-=p; 61 if(x+x>=p) x -= p; 62 } 63 } else { 64 p_half = 0.5*p; 65 if(x>p_half) { 66 x-=p; 67 if(x>=p_half) x -= p; 68 } 69 } 70 GET_HIGH_WORD(hx,x); 71 SET_HIGH_WORD(x,hx^sx); 72 return x; 73 } 74