s_ceill.c revision 145637 
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_ceil.c 5.1 93/09/24
12 */
13
14#ifndef lint
15static char rcsid[] = "$FreeBSD: head/lib/msun/src/s_ceill.c 145637 2005-04-28 19:45:55Z stefanf $";
16#endif
17
18/*
19 * ceill(x)
20 * Return x rounded toward -inf to integral value
21 * Method:
22 *	Bit twiddling.
23 * Exception:
24 *	Inexact flag raised if x not equal to ceill(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#define	INC_MANH(u, c)	do {					\
36	uint64_t o = u.bits.manh;				\
37	u.bits.manh += (c);					\
38	if (u.bits.manh < o)					\
39		u.bits.exp++;					\
40} while (0)
41#else
42#define	MANH_SIZE	LDBL_MANH_SIZE
43#define	INC_MANH(u, c)	do {					\
44	uint64_t o = u.bits.manh;				\
45	u.bits.manh += (c);					\
46	if (u.bits.manh < o) {					\
47		u.bits.exp++;					\
48		u.bits.manh |= 1llu << (LDBL_MANH_SIZE - 1);	\
49	}							\
50} while (0)
51#endif
52
53static const long double huge = 1.0e300;
54
55long double
56ceill(long double x)
57{
58	union IEEEl2bits u = { .e = x };
59	int e = u.bits.exp - LDBL_MAX_EXP + 1;
60
61	if (e < MANH_SIZE - 1) {
62		if (e < 0) {			/* raise inexact if x != 0 */
63			if (huge + x > 0.0)
64				if (u.bits.exp > 0 ||
65				    (u.bits.manh | u.bits.manl) != 0)
66					u.e = u.bits.sign ? 0.0 : 1.0;
67		} else {
68			uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
69			if (((u.bits.manh & m) | u.bits.manl) == 0)
70				return (x);	/* x is integral */
71			if (!u.bits.sign) {
72#ifdef LDBL_IMPLICIT_NBIT
73				if (e == 0)
74					u.bits.exp++;
75				else
76#endif
77				INC_MANH(u, 1llu << (MANH_SIZE - e - 1));
78			}
79			if (huge + x > 0.0) {	/* raise inexact flag */
80				u.bits.manh &= ~m;
81				u.bits.manl = 0;
82			}
83		}
84	} else if (e < LDBL_MANT_DIG - 1) {
85		uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
86		if ((u.bits.manl & m) == 0)
87			return (x);	/* x is integral */
88		if (!u.bits.sign) {
89			if (e == MANH_SIZE - 1)
90				INC_MANH(u, 1);
91			else {
92				uint64_t o = u.bits.manl;
93				u.bits.manl += 1llu << (LDBL_MANT_DIG - e - 1);
94				if (u.bits.manl < o)	/* got a carry */
95					INC_MANH(u, 1);
96			}
97		}
98		if (huge + x > 0.0)		/* raise inexact flag */
99			u.bits.manl &= ~m;
100	}
101	return (u.e);
102}
103