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