/*-
 * Copyright (c) 2007 David Schultz <das@FreeBSD.ORG>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * Derived from s_modf.c, which has the following Copyright:
 * ====================================================
 * 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.
 * ====================================================
 *
 * $FreeBSD: head/lib/msun/src/s_modfl.c 165855 2007-01-07 07:54:21Z das $
 */
#include <sys/cdefs.h>
__RCSID("$NetBSD: s_modfl.c,v 1.2 2024/05/15 00:02:56 riastradh Exp $");

#include "namespace.h"

#include <float.h>
#include <math.h>
#include <stdint.h>
#include <machine/ieee.h>

#ifdef __HAVE_LONG_DOUBLE

#ifdef __weak_alias
__weak_alias(modfl, _modfl)
#endif

#if EXT_FRACLBITS > 32
#define MASK    ((uint64_t)-1)
#else
#define MASK    ((uint32_t)-1)
#endif
/* Return the last n bits of a word, representing the fractional part. */
#define GETFRAC(bits, n)        ((bits) & ~(MASK << (n)))
/* The number of fraction bits in manh, not counting the integer bit */
#define HIBITS  (LDBL_MANT_DIG - EXT_FRACLBITS)

static const long double zero[] = { 0.0L, -0.0L };

long double
modfl(long double x, long double *iptr)
{
        union ieee_ext_u ux = { .extu_ld = x, };
        int e = ux.extu_exp - LDBL_MAX_EXP + 1;

        if (e < HIBITS) {                       /* Integer part is in manh. */
                if (e < 0) {                    /* |x|<1 */
                        *iptr = zero[ux.extu_sign];
                        return (x);
                } else {
                        if ((GETFRAC(ux.extu_frach, HIBITS - 1 - e) |
                             ux.extu_fracl) == 0) {     /* X is an integer. */
                                *iptr = x;
                                return (zero[ux.extu_sign]);
                        } else {
                                /* Clear all but the top e+1 bits. */
                                ux.extu_frach >>= HIBITS - 1 - e;
                                ux.extu_frach <<= HIBITS - 1 - e;
                                ux.extu_fracl = 0;
                                *iptr = ux.extu_ld;
                                return (x - ux.extu_ld);
                        }
                }
        } else if (e >= LDBL_MANT_DIG - 1) {    /* x has no fraction part. */
                *iptr = x;
                if (x != x)                     /* Handle NaNs. */
                        return (x);
                return (zero[ux.extu_sign]);
        } else {                                /* Fraction part is in manl. */
                if (GETFRAC(ux.extu_fracl, LDBL_MANT_DIG - 1 - e) == 0) {
                        /* x is integral. */
                        *iptr = x;
                        return (zero[ux.extu_sign]);
                } else {
                        /* Clear all but the top e+1 bits. */
                        ux.extu_fracl >>= LDBL_MANT_DIG - 1 - e;
                        ux.extu_fracl <<= LDBL_MANT_DIG - 1 - e;
                        *iptr = ux.extu_ld;
                        return (x - ux.extu_ld);
                }
        }
}
#endif /* __HAVE_LONG_DOUBLE */