s_rint.c revision 97413 
1/* @(#)s_rint.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
14static char rcsid[] = "$FreeBSD: head/lib/msun/src/s_rint.c 97413 2002-05-28 18:15:04Z alfred $";
15#endif
16
17/*
18 * rint(x)
19 * Return x rounded to integral value according to the prevailing
20 * rounding mode.
21 * Method:
22 *	Using floating addition.
23 * Exception:
24 *	Inexact flag raised if x not equal to rint(x).
25 */
26
27#include "math.h"
28#include "math_private.h"
29
30/*
31 * TWO23 is long double instead of double to avoid a bug in gcc.  Without
32 * this, gcc thinks that TWO23[sx]+x and w-TWO23[sx] already have double
33 * precision and doesn't clip them to double precision when they are
34 * assigned and returned.  Use long double even in the !__STDC__ case in
35 * case this is compiled with gcc -traditional.
36 */
37static const long double
38TWO52[2]={
39  4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
40 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
41};
42
43double
44__generic_rint(double x)
45{
46	int32_t i0,j0,sx;
47	u_int32_t i,i1;
48	double w,t;
49	EXTRACT_WORDS(i0,i1,x);
50	sx = (i0>>31)&1;
51	j0 = ((i0>>20)&0x7ff)-0x3ff;
52	if(j0<20) {
53	    if(j0<0) {
54		if(((i0&0x7fffffff)|i1)==0) return x;
55		i1 |= (i0&0x0fffff);
56		i0 &= 0xfffe0000;
57		i0 |= ((i1|-i1)>>12)&0x80000;
58		SET_HIGH_WORD(x,i0);
59	        w = TWO52[sx]+x;
60	        t =  w-TWO52[sx];
61		GET_HIGH_WORD(i0,t);
62		SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
63	        return t;
64	    } else {
65		i = (0x000fffff)>>j0;
66		if(((i0&i)|i1)==0) return x; /* x is integral */
67		i>>=1;
68		if(((i0&i)|i1)!=0) {
69		    if(j0==19) i1 = 0x40000000; else
70		    i0 = (i0&(~i))|((0x20000)>>j0);
71		}
72	    }
73	} else if (j0>51) {
74	    if(j0==0x400) return x+x;	/* inf or NaN */
75	    else return x;		/* x is integral */
76	} else {
77	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
78	    if((i1&i)==0) return x;	/* x is integral */
79	    i>>=1;
80	    if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
81	}
82	INSERT_WORDS(x,i0,i1);
83	w = TWO52[sx]+x;
84	return w-TWO52[sx];
85}
86