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| 2 | /* @(#)e_remainder.c 5.1 93/09/24 */ |
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| 3 | /* |
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| 4 | * ==================================================== |
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| 5 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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| 6 | * |
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| 7 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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| 8 | * Permission to use, copy, modify, and distribute this |
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| 9 | * software is freely granted, provided that this notice |
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| 10 | * is preserved. |
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| 11 | * ==================================================== |
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| 12 | */ |
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| 13 | |
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| 14 | /* __ieee754_remainder(x,p) |
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| 15 | * Return : |
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| 16 | * returns x REM p = x - [x/p]*p as if in infinite |
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| 17 | * precise arithmetic, where [x/p] is the (infinite bit) |
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| 18 | * integer nearest x/p (in half way case choose the even one). |
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| 19 | * Method : |
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| 20 | * Based on fmod() return x-[x/p]chopped*p exactlp. |
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| 21 | */ |
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| 22 | |
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| 23 | #include <libm/fdlibm.h> |
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| 24 | |
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| 25 | #ifdef __STDC__ |
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| 26 | static const double zero = 0.0, one = 1.0; |
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| 27 | #else |
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| 28 | static double zero = 0.0, one = 1.0; |
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| 29 | #endif |
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| 30 | |
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| 31 | |
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| 32 | #ifdef __STDC__ |
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| 33 | double __ieee754_remainder(double x, double p) |
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| 34 | #else |
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| 35 | double __ieee754_remainder(x,p) |
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| 36 | double x,p; |
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| 37 | #endif |
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| 38 | { |
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| 39 | int hx,hp,n0,n1; |
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| 40 | unsigned sx,lx,lp; |
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| 41 | double p_half; |
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| 42 | |
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| 43 | n0 = ((*(int*)&one)>>29)^1; /* index of high word */ |
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| 44 | n1 = 1-n0; /* index of low word */ |
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| 45 | hx = *( n0 + (int*)&x); /* high word of x */ |
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| 46 | lx = *( n1 + (int*)&x); /* low word of x */ |
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| 47 | hp = *( n0 + (int*)&p); /* high word of p */ |
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| 48 | lp = *( n1 + (int*)&p); /* low word of p */ |
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| 49 | sx = hx&0x80000000; |
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| 50 | hp &= 0x7fffffff; |
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| 51 | hx &= 0x7fffffff; |
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| 52 | |
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| 53 | /* purge off exception values */ |
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| 54 | if((hp|lp)==0) return (x*p)/(x*p); /* p = 0 */ |
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| 55 | if((hx>=0x7ff00000)|| /* x not finite */ |
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| 56 | ((hp>=0x7ff00000)&& /* p is NaN */ |
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| 57 | (((hp-0x7ff00000)|lp)!=0))) |
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| 58 | return (x*p)/(x*p); |
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| 59 | |
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| 60 | |
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| 61 | if (hp<=0x7fdfffff) x = __ieee754_fmod(x,p+p); /* now x < 2p */ |
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| 62 | if (((hx-hp)|(lx-lp))==0) return zero*x; |
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| 63 | x = fabs(x); |
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| 64 | p = fabs(p); |
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| 65 | if (hp<0x00200000) { |
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| 66 | if(x+x>p) { |
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| 67 | x-=p; |
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| 68 | if(x+x>=p) x -= p; |
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| 69 | } |
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| 70 | } else { |
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| 71 | p_half = 0.5*p; |
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| 72 | if(x>p_half) { |
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| 73 | x-=p; |
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| 74 | if(x>=p_half) x -= p; |
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| 75 | } |
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| 76 | } |
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| 77 | *(n0+(int*)&x) ^= sx; |
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| 78 | return x; |
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| 79 | } |
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