s_rint.c revision 2116 
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[] = "$Id: s_rint.c,v 1.6 1994/08/18 23:07:16 jtc Exp $";
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#ifdef __STDC__
31static const double
32#else
33static double
34#endif
35TWO52[2]={
36  4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
37 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
38};
39
40#ifdef __STDC__
41	double rint(double x)
42#else
43	double rint(x)
44	double x;
45#endif
46{
47	int32_t i0,j0,sx;
48	u_int32_t i,i1;
49	double w,t;
50	EXTRACT_WORDS(i0,i1,x);
51	sx = (i0>>31)&1;
52	j0 = ((i0>>20)&0x7ff)-0x3ff;
53	if(j0<20) {
54	    if(j0<0) {
55		if(((i0&0x7fffffff)|i1)==0) return x;
56		i1 |= (i0&0x0fffff);
57		i0 &= 0xfffe0000;
58		i0 |= ((i1|-i1)>>12)&0x80000;
59		SET_HIGH_WORD(x,i0);
60	        w = TWO52[sx]+x;
61	        t =  w-TWO52[sx];
62		GET_HIGH_WORD(i0,t);
63		SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
64	        return t;
65	    } else {
66		i = (0x000fffff)>>j0;
67		if(((i0&i)|i1)==0) return x; /* x is integral */
68		i>>=1;
69		if(((i0&i)|i1)!=0) {
70		    if(j0==19) i1 = 0x40000000; else
71		    i0 = (i0&(~i))|((0x20000)>>j0);
72		}
73	    }
74	} else if (j0>51) {
75	    if(j0==0x400) return x+x;	/* inf or NaN */
76	    else return x;		/* x is integral */
77	} else {
78	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
79	    if((i1&i)==0) return x;	/* x is integral */
80	    i>>=1;
81	    if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
82	}
83	INSERT_WORDS(x,i0,i1);
84	w = TWO52[sx]+x;
85	return w-TWO52[sx];
86}
87