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#include <sys/cdefs.h>
14__FBSDID("$FreeBSD$");
15
16/*
17 * rint(x)
18 * Return x rounded to integral value according to the prevailing
19 * rounding mode.
20 * Method:
21 *	Using floating addition.
22 * Exception:
23 *	Inexact flag raised if x not equal to rint(x).
24 */
25
26#include <float.h>
27
28#include "math.h"
29#include "math_private.h"
30
31static const double
32TWO52[2]={
33  4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
34 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
35};
36
37double
38rint(double x)
39{
40	int32_t i0,j0,sx;
41	u_int32_t i,i1;
42	double w,t;
43	EXTRACT_WORDS(i0,i1,x);
44	sx = (i0>>31)&1;
45	j0 = ((i0>>20)&0x7ff)-0x3ff;
46	if(j0<20) {
47	    if(j0<0) {
48		if(((i0&0x7fffffff)|i1)==0) return x;
49		i1 |= (i0&0x0fffff);
50		i0 &= 0xfffe0000;
51		i0 |= ((i1|-i1)>>12)&0x80000;
52		SET_HIGH_WORD(x,i0);
53	        STRICT_ASSIGN(double,w,TWO52[sx]+x);
54	        t =  w-TWO52[sx];
55		GET_HIGH_WORD(i0,t);
56		SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
57	        return t;
58	    } else {
59		i = (0x000fffff)>>j0;
60		if(((i0&i)|i1)==0) return x; /* x is integral */
61		i>>=1;
62		if(((i0&i)|i1)!=0) {
63		    /*
64		     * Some bit is set after the 0.5 bit.  To avoid the
65		     * possibility of errors from double rounding in
66		     * w = TWO52[sx]+x, adjust the 0.25 bit to a lower
67		     * guard bit.  We do this for all j0<=51.  The
68		     * adjustment is trickiest for j0==18 and j0==19
69		     * since then it spans the word boundary.
70		     */
71		    if(j0==19) i1 = 0x40000000; else
72		    if(j0==18) i1 = 0x80000000; else
73		    i0 = (i0&(~i))|((0x20000)>>j0);
74		}
75	    }
76	} else if (j0>51) {
77	    if(j0==0x400) return x+x;	/* inf or NaN */
78	    else return x;		/* x is integral */
79	} else {
80	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
81	    if((i1&i)==0) return x;	/* x is integral */
82	    i>>=1;
83	    if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
84	}
85	INSERT_WORDS(x,i0,i1);
86	STRICT_ASSIGN(double,w,TWO52[sx]+x);
87	return w-TWO52[sx];
88}
89
90#if (LDBL_MANT_DIG == 53)
91__weak_reference(rint, rintl);
92#endif
93