xref: /minix3/lib/libm/src/s_rint.c (revision 2fe8fb192fe7e8720e3e7a77f928da545e872a6a)
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 #if defined(LIBM_SCCS) && !defined(lint)
15 __RCSID("$NetBSD: s_rint.c,v 1.12 2008/04/25 22:21:53 christos Exp $");
16 #endif
17 
18 /*
19  * rint(x)
20  * Return x rounded to integral value according to the prevailing
21  * rounding mode.
22  * Method:
23  *	Using floating addition.
24  * Exception:
25  *	Inexact flag raised if x not equal to rint(x).
26  */
27 
28 #include "math.h"
29 #include "math_private.h"
30 
31 static const double
32 TWO52[2]={
33   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
34  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
35 };
36 
37 double
rint(double x)38 rint(double x)
39 {
40 	int32_t i0,jj0,sx;
41 	u_int32_t i,i1;
42 	double w,t;
43 	EXTRACT_WORDS(i0,i1,x);
44 	sx = (i0>>31)&1;
45 	jj0 = ((i0>>20)&0x7ff)-0x3ff;
46 	if(jj0<20) {
47 	    if(jj0<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 	        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)>>jj0;
60 		if(((i0&i)|i1)==0) return x; /* x is integral */
61 		i>>=1;
62 		if(((i0&i)|i1)!=0) {
63 		    if(jj0==19) i1 = 0x40000000; else
64 		    i0 = (i0&(~i))|((0x20000)>>jj0);
65 		}
66 	    }
67 	} else if (jj0>51) {
68 	    if(jj0==0x400) return x+x;	/* inf or NaN */
69 	    else return x;		/* x is integral */
70 	} else {
71 	    i = ((u_int32_t)(0xffffffff))>>(jj0-20);
72 	    if((i1&i)==0) return x;	/* x is integral */
73 	    i>>=1;
74 	    if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(jj0-20));
75 	}
76 	INSERT_WORDS(x,i0,i1);
77 	w = TWO52[sx]+x;
78 	return w-TWO52[sx];
79 }
80