projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| 4acf9396 GCI |
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[] = "$Id: e_remainder.c,v 1.4 1994/03/03 17:04:20 jtc 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 <machine/endian.h> | |
| 28 | ||
| 29 | #if BYTE_ORDER == LITTLE_ENDIAN | |
| 30 | #define n0 1 | |
| 31 | #define n1 0 | |
| 32 | #else | |
| 33 | #define n0 0 | |
| 34 | #define n1 1 | |
| 35 | #endif | |
| 36 | ||
| 37 | #ifdef __STDC__ | |
| 38 | static const double zero = 0.0; | |
| 39 | #else | |
| 40 | static double zero = 0.0; | |
| 41 | #endif | |
| 42 | ||
| 43 | ||
| 44 | #ifdef __STDC__ | |
| 45 | double __ieee754_remainder(double x, double p) | |
| 46 | #else | |
| 47 | double __ieee754_remainder(x,p) | |
| 48 | double x,p; | |
| 49 | #endif | |
| 50 | { | |
| 51 | int hx,hp; | |
| 52 | unsigned sx,lx,lp; | |
| 53 | double p_half; | |
| 54 | ||
| 55 | hx = *( n0 + (int*)&x); /* high word of x */ | |
| 56 | lx = *( n1 + (int*)&x); /* low word of x */ | |
| 57 | hp = *( n0 + (int*)&p); /* high word of p */ | |
| 58 | lp = *( n1 + (int*)&p); /* low word of p */ | |
| 59 | sx = hx&0x80000000; | |
| 60 | hp &= 0x7fffffff; | |
| 61 | hx &= 0x7fffffff; | |
| 62 | ||
| 63 | /* purge off exception values */ | |
| 64 | if((hp|lp)==0) return (x*p)/(x*p); /* p = 0 */ | |
| 65 | if((hx>=0x7ff00000)|| /* x not finite */ | |
| 66 | ((hp>=0x7ff00000)&& /* p is NaN */ | |
| 67 | (((hp-0x7ff00000)|lp)!=0))) | |
| 68 | return (x*p)/(x*p); | |
| 69 | ||
| 70 | ||
| 71 | if (hp<=0x7fdfffff) x = __ieee754_fmod(x,p+p); /* now x < 2p */ | |
| 72 | if (((hx-hp)|(lx-lp))==0) return zero*x; | |
| 73 | x = fabs(x); | |
| 74 | p = fabs(p); | |
| 75 | if (hp<0x00200000) { | |
| 76 | if(x+x>p) { | |
| 77 | x-=p; | |
| 78 | if(x+x>=p) x -= p; | |
| 79 | } | |
| 80 | } else { | |
| 81 | p_half = 0.5*p; | |
| 82 | if(x>p_half) { | |
| 83 | x-=p; | |
| 84 | if(x>=p_half) x -= p; | |
| 85 | } | |
| 86 | } | |
| 87 | *(n0+(int*)&x) ^= sx; | |
| 88 | return x; | |
| 89 | } |