s_rint.c revision 175309 
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 175309 2008-01-14 02:12:07Z das $";
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 <float.h>
28
29#include "math.h"
30#include "math_private.h"
31
32static const double
33TWO52[2]={
34  4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
35 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
36};
37
38double
39rint(double x)
40{
41	int32_t i0,j0,sx;
42	u_int32_t i,i1;
43	double w,t;
44	EXTRACT_WORDS(i0,i1,x);
45	sx = (i0>>31)&1;
46	j0 = ((i0>>20)&0x7ff)-0x3ff;
47	if(j0<20) {
48	    if(j0<0) {
49		if(((i0&0x7fffffff)|i1)==0) return x;
50		i1 |= (i0&0x0fffff);
51		i0 &= 0xfffe0000;
52		i0 |= ((i1|-i1)>>12)&0x80000;
53		SET_HIGH_WORD(x,i0);
54	        w = TWO52[sx]+x;
55	        t =  w-TWO52[sx];
56		GET_HIGH_WORD(i0,t);
57		SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
58	        return t;
59	    } else {
60		i = (0x000fffff)>>j0;
61		if(((i0&i)|i1)==0) return x; /* x is integral */
62		i>>=1;
63		if(((i0&i)|i1)!=0) {
64		    /*
65		     * Some bit is set after the 0.5 bit.  To avoid the
66		     * possibility of errors from double rounding in
67		     * w = TWO52[sx]+x, adjust the 0.25 bit to a lower
68		     * guard bit.  We do this for all j0<=51.  The
69		     * adjustment is trickiest for j0==18 and j0==19
70		     * since then it spans the word boundary.
71		     */
72		    if(j0==19) i1 = 0x40000000; else
73		    if(j0==18) i1 = 0x80000000; else
74		    i0 = (i0&(~i))|((0x20000)>>j0);
75		}
76	    }
77	} else if (j0>51) {
78	    if(j0==0x400) return x+x;	/* inf or NaN */
79	    else return x;		/* x is integral */
80	} else {
81	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
82	    if((i1&i)==0) return x;	/* x is integral */
83	    i>>=1;
84	    if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
85	}
86	INSERT_WORDS(x,i0,i1);
87	*(volatile double *)&w = TWO52[sx]+x;	/* clip any extra precision */
88	return w-TWO52[sx];
89}
90
91#if (LDBL_MANT_DIG == 53)
92__weak_reference(rint, rintl);
93#endif
94