| 1 | /* @(#)s_rint.c 5.1 93/09/24 */
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| 2 | /*
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| 3 | * ====================================================
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| 4 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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| 5 | *
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| 6 | * Developed at SunPro, a Sun Microsystems, Inc. business.
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| 7 | * Permission to use, copy, modify, and distribute this
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| 8 | * software is freely granted, provided that this notice
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| 9 | * is preserved.
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| 10 | * ====================================================
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| 11 | */
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| 12 |
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| 13 | #ifndef lint
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| 14 | static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_rint.c,v 1.11 2005/03/07 20:28:26 stefanf Exp $";
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| 15 | #endif
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| 16 |
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| 17 | /*
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| 18 | * rint(x)
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| 19 | * Return x rounded to integral value according to the prevailing
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| 20 | * rounding mode.
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| 21 | * Method:
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| 22 | * Using floating addition.
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| 23 | * Exception:
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| 24 | * Inexact flag raised if x not equal to rint(x).
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| 25 | */
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| 26 |
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| 27 | #include "math.h"
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| 28 | #include "math_private.h"
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| 29 |
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| 30 | /*
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| 31 | * TWO23 is long double instead of double to avoid a bug in gcc. Without
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| 32 | * this, gcc thinks that TWO23[sx]+x and w-TWO23[sx] already have double
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| 33 | * precision and doesn't clip them to double precision when they are
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| 34 | * assigned and returned.
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| 35 | */
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| 36 | static const long double
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| 37 | TWO52[2]={
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| 38 | 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
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| 39 | -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
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| 40 | };
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| 41 |
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| 42 | double
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| 43 | rint(double x)
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| 44 | {
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| 45 | int32_t i0,j0,sx;
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| 46 | u_int32_t i,i1;
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| 47 | double w,t;
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| 48 | EXTRACT_WORDS(i0,i1,x);
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| 49 | sx = (i0>>31)&1;
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| 50 | j0 = ((i0>>20)&0x7ff)-0x3ff;
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| 51 | if(j0<20) {
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| 52 | if(j0<0) {
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| 53 | if(((i0&0x7fffffff)|i1)==0) return x;
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| 54 | i1 |= (i0&0x0fffff);
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| 55 | i0 &= 0xfffe0000;
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| 56 | i0 |= ((i1|-i1)>>12)&0x80000;
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| 57 | SET_HIGH_WORD(x,i0);
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| 58 | w = TWO52[sx]+x;
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| 59 | t = w-TWO52[sx];
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| 60 | GET_HIGH_WORD(i0,t);
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| 61 | SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
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| 62 | return t;
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| 63 | } else {
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| 64 | i = (0x000fffff)>>j0;
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| 65 | if(((i0&i)|i1)==0) return x; /* x is integral */
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| 66 | i>>=1;
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| 67 | if(((i0&i)|i1)!=0) {
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| 68 | if(j0==19) i1 = 0x40000000; else
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| 69 | i0 = (i0&(~i))|((0x20000)>>j0);
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| 70 | }
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| 71 | }
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| 72 | } else if (j0>51) {
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| 73 | if(j0==0x400) return x+x; /* inf or NaN */
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| 74 | else return x; /* x is integral */
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| 75 | } else {
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| 76 | i = ((u_int32_t)(0xffffffff))>>(j0-20);
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| 77 | if((i1&i)==0) return x; /* x is integral */
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| 78 | i>>=1;
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| 79 | if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
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| 80 | }
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| 81 | INSERT_WORDS(x,i0,i1);
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| 82 | w = TWO52[sx]+x;
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| 83 | return w-TWO52[sx];
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| 84 | }
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