| 1 | |
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| 2 | /* @(#)s_rint.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 | /* |
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| 15 | * rint(x) |
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| 16 | * Return x rounded to integral value according to the prevailing |
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| 17 | * rounding mode. |
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| 18 | * Method: |
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| 19 | * Using floating addition. |
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| 20 | * Exception: |
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| 21 | * Inexact flag raised if x not equal to rint(x). |
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| 22 | */ |
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| 23 | |
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| 24 | #include <libm/fdlibm.h> |
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| 25 | |
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| 26 | #ifdef __STDC__ |
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| 27 | static const double |
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| 28 | #else |
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| 29 | static double |
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| 30 | #endif |
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| 31 | one = 1.0, |
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| 32 | TWO52[2]={ |
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| 33 | 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */ |
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| 34 | -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */ |
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| 35 | }; |
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| 36 | |
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| 37 | #ifdef __STDC__ |
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| 38 | double rint(double x) |
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| 39 | #else |
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| 40 | double rint(x) |
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| 41 | double x; |
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| 42 | #endif |
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| 43 | { |
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| 44 | int i0,n0,j0,sx; |
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| 45 | unsigned i,i1; |
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| 46 | double w,t; |
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| 47 | n0 = (*((int *)&one)>>29)^1; |
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| 48 | i0 = *(n0+(int*)&x); |
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| 49 | sx = (i0>>31)&1; |
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| 50 | i1 = *(1-n0+(int*)&x); |
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| 51 | j0 = ((i0>>20)&0x7ff)-0x3ff; |
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| 52 | if(j0<20) { |
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| 53 | if(j0<0) { |
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| 54 | if(((i0&0x7fffffff)|i1)==0) return x; |
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| 55 | i1 |= (i0&0x0fffff); |
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| 56 | i0 &= 0xfffe0000; |
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| 57 | i0 |= ((i1|-i1)>>12)&0x80000; |
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| 58 | *(n0+(int*)&x)=i0; |
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| 59 | w = TWO52[sx]+x; |
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| 60 | t = w-TWO52[sx]; |
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| 61 | i0 = *(n0+(int*)&t); |
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| 62 | *(n0+(int*)&t) = (i0&0x7fffffff)|(sx<<31); |
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| 63 | return t; |
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| 64 | } else { |
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| 65 | i = (0x000fffff)>>j0; |
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| 66 | if(((i0&i)|i1)==0) return x; /* x is integral */ |
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| 67 | i>>=1; |
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| 68 | if(((i0&i)|i1)!=0) { |
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| 69 | if(j0==19) i1 = 0x40000000; else |
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| 70 | i0 = (i0&(~i))|((0x20000)>>j0); |
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| 71 | } |
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| 72 | } |
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| 73 | } else if (j0>51) { |
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| 74 | if(j0==0x400) return x+x; /* inf or NaN */ |
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| 75 | else return x; /* x is integral */ |
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| 76 | } else { |
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| 77 | i = ((unsigned)(0xffffffff))>>(j0-20); |
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| 78 | if((i1&i)==0) return x; /* x is integral */ |
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| 79 | i>>=1; |
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| 80 | if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20)); |
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| 81 | } |
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| 82 | *(n0+(int*)&x) = i0; |
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| 83 | *(1-n0+(int*)&x) = i1; |
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| 84 | w = TWO52[sx]+x; |
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| 85 | return w-TWO52[sx]; |
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| 86 | } |
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