s_truncl.c revision 145170 
1/*
2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4 *
5 * Developed at SunPro, a Sun Microsystems, Inc. business.
6 * Permission to use, copy, modify, and distribute this
7 * software is freely granted, provided that this notice
8 * is preserved.
9 * ====================================================
10 *
11 * From: @(#)s_floor.c 5.1 93/09/24
12 */
13
14#ifndef lint
15static char rcsid[] = "$FreeBSD: head/lib/msun/src/s_truncl.c 145170 2005-04-16 21:12:47Z das $";
16#endif
17
18/*
19 * truncl(x)
20 * Return x rounded toward 0 to integral value
21 * Method:
22 *	Bit twiddling.
23 * Exception:
24 *	Inexact flag raised if x not equal to truncl(x).
25 */
26
27#include <float.h>
28#include <math.h>
29#include <stdint.h>
30
31#include "fpmath.h"
32
33#ifdef LDBL_IMPLICIT_NBIT
34#define	MANH_SIZE	(LDBL_MANH_SIZE + 1)
35#else
36#define	MANH_SIZE	LDBL_MANH_SIZE
37#endif
38
39long double
40truncl(long double x)
41{
42	union IEEEl2bits u = { .e = x };
43	int e = u.bits.exp - LDBL_MAX_EXP + 1;
44
45	if (e < MANH_SIZE - 1) {
46		if (e < 0) {			/* raise inexact if x != 0 */
47			u.e = 0.0;
48		} else {
49			uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
50			if (((u.bits.manh & m) | u.bits.manl) == 0)
51				return (x);	/* x is integral */
52			u.bits.manh &= ~m;
53			u.bits.manl = 0;
54		}
55	} else if (e < LDBL_MANT_DIG - 1) {
56		uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
57		if ((u.bits.manl & m) == 0)
58			return (x);	/* x is integral */
59		u.bits.manl &= ~m;
60	}
61	return (u.e);
62}
63