source: vendor/FreeBSD-msun/current/src/s_ceill.c

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 *
 * From: @(#)s_ceil.c 5.1 93/09/24
 */

#ifndef lint
static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_ceill.c,v 1.3 2005/04/22 09:57:55 stefanf Exp $";
#endif

/*
 * ceill(x)
 * Return x rounded toward -inf to integral value
 * Method:
 *      Bit twiddling.
 * Exception:
 *      Inexact flag raised if x not equal to ceill(x).
 */

#include <float.h>
#include <math.h>
#include <stdint.h>

#include "fpmath.h"

#ifdef LDBL_IMPLICIT_NBIT
#define MANH_SIZE       (LDBL_MANH_SIZE + 1)
#define INC_MANH(u, c)  do {                                    \
        uint64_t o = u.bits.manh;                               \
        u.bits.manh += (c);                                     \
        if (u.bits.manh < o)                                    \
                u.bits.exp++;                                   \
} while (0)
#else
#define MANH_SIZE       LDBL_MANH_SIZE
#define INC_MANH(u, c)  do {                                    \
        uint64_t o = u.bits.manh;                               \
        u.bits.manh += (c);                                     \
        if (u.bits.manh < o) {                                  \
                u.bits.exp++;                                   \
                u.bits.manh |= 1llu << (LDBL_MANH_SIZE - 1);    \
        }                                                       \
} while (0)
#endif

static const double huge = 1.0e300;

long double
ceill(long double x)
{
        union IEEEl2bits u = { .e = x };
        int e = u.bits.exp - LDBL_MAX_EXP + 1;

        if (e < MANH_SIZE - 1) {
                if (e < 0) {                    /* raise inexact if x != 0 */
                        if (huge + (double)x > 0.0)
                                if (u.bits.exp > 0 ||
                                    (u.bits.manh | u.bits.manl) != 0)
                                        u.e = u.bits.sign ? 0.0 : 1.0;
                } else {
                        uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
                        if (((u.bits.manh & m) | u.bits.manl) == 0)
                                return (x);     /* x is integral */
                        if (!u.bits.sign) {
#ifdef LDBL_IMPLICIT_NBIT
                                if (e == 0)
                                        u.bits.exp++;
                                else
#endif
                                INC_MANH(u, 1llu << (MANH_SIZE - e - 1));
                        }
                        if (huge + (double)x > 0.0) {   /* raise inexact flag */
                                u.bits.manh &= ~m;
                                u.bits.manl = 0;
                        }
                }
        } else if (e < LDBL_MANT_DIG - 1) {
                uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
                if ((u.bits.manl & m) == 0)
                        return (x);     /* x is integral */
                if (!u.bits.sign) {
                        if (e == MANH_SIZE - 1)
                                INC_MANH(u, 1);
                        else {
                                uint64_t o = u.bits.manl;
                                u.bits.manl += 1llu << (LDBL_MANT_DIG - e - 1);
                                if (u.bits.manl < o)    /* got a carry */
                                        INC_MANH(u, 1);
                        }
                }
                if (huge + (double)x > 0.0)     /* raise inexact flag */
                        u.bits.manl &= ~m;
        }
        return (u.e);
}