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: src/lib/msun/src/s_rint.c,v 1.13 2005/12/03 07:38:35 bde 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
30static const double
31TWO52[2]={
32  4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
33 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
34};
35
36double
37rint(double x)
38{
39	int32_t i0,j0,sx;
40	u_int32_t i,i1;
41	double w,t;
42	EXTRACT_WORDS(i0,i1,x);
43	sx = (i0>>31)&1;
44	j0 = ((i0>>20)&0x7ff)-0x3ff;
45	if(j0<20) {
46	    if(j0<0) {
47		if(((i0&0x7fffffff)|i1)==0) return x;
48		i1 |= (i0&0x0fffff);
49		i0 &= 0xfffe0000;
50		i0 |= ((i1|-i1)>>12)&0x80000;
51		SET_HIGH_WORD(x,i0);
52	        w = TWO52[sx]+x;
53	        t =  w-TWO52[sx];
54		GET_HIGH_WORD(i0,t);
55		SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
56	        return t;
57	    } else {
58		i = (0x000fffff)>>j0;
59		if(((i0&i)|i1)==0) return x; /* x is integral */
60		i>>=1;
61		if(((i0&i)|i1)!=0) {
62		    /*
63		     * Some bit is set after the 0.5 bit.  To avoid the
64		     * possibility of errors from double rounding in
65		     * w = TWO52[sx]+x, adjust the 0.25 bit to a lower
66		     * guard bit.  We do this for all j0<=51.  The
67		     * adjustment is trickiest for j0==18 and j0==19
68		     * since then it spans the word boundary.
69		     */
70		    if(j0==19) i1 = 0x40000000; else
71		    if(j0==18) i1 = 0x80000000; else
72		    i0 = (i0&(~i))|((0x20000)>>j0);
73		}
74	    }
75	} else if (j0>51) {
76	    if(j0==0x400) return x+x;	/* inf or NaN */
77	    else return x;		/* x is integral */
78	} else {
79	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
80	    if((i1&i)==0) return x;	/* x is integral */
81	    i>>=1;
82	    if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
83	}
84	INSERT_WORDS(x,i0,i1);
85	*(volatile double *)&w = TWO52[sx]+x;	/* clip any extra precision */
86	return w-TWO52[sx];
87}
88