/*      $NetBSD: s_nexttoward.c,v 1.3 2024/05/11 02:07:53 riastradh Exp $       */

/* @(#)s_nextafter.c 5.1 93/09/24 */
/*
 * ====================================================
 * 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.
 * ====================================================
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: s_nexttoward.c,v 1.3 2024/05/11 02:07:53 riastradh Exp $");

/*
 * We assume that a long double has a 15-bit exponent.  On systems
 * where long double is the same as double, nexttoward() is an alias
 * for nextafter(), so we don't use this routine.
 */
#include <float.h>

#include <machine/ieee.h>
#include "math.h"
#include "math_private.h"

#if LDBL_MAX_EXP != 0x4000
#error "Unsupported long double format"
#endif

#ifdef LDBL_IMPLICIT_NBIT
#define LDBL_NBIT       0
#endif

/*
 * The nexttoward() function is equivalent to nextafter() function,
 * except that the second parameter shall have type long double and
 * the functions shall return y converted to the type of the function
 * if x equals y.
 *
 * Special cases: XXX
 */
double
nexttoward(double x, long double y)
{
        union ieee_ext_u uy;
        volatile double t;
        int32_t hx, ix;
        uint32_t lx;

        EXTRACT_WORDS(hx, lx, x);
        ix = hx & 0x7fffffff;                   /* |x| */
        uy.extu_ld = y;

        if (((ix >= 0x7ff00000) && ((ix - 0x7ff00000) | lx) != 0) ||
            (uy.extu_exp == 0x7fff &&
                ((uy.extu_frach & ~LDBL_NBIT) | uy.extu_fracl) != 0))
                return x+y;                     /* x or y is nan */

        if (x == y)
                return (double)y;               /* x=y, return y */

        if (x == 0.0) {
                INSERT_WORDS(x, uy.extu_sign<<31, 1);   /* return +-minsubnormal */
                t = x*x;
                if (t == x)
                        return t;
                else
                        return x;               /* raise underflow flag */
        }

        if ((hx >= 0) ^ (x < y)) {              /* x -= ulp */
                if (lx == 0) hx -= 1;
                lx -= 1;
        } else {                                /* x += ulp */
                lx += 1;
                if (lx == 0) hx += 1;
        }
        ix = hx & 0x7ff00000;
        if (ix >= 0x7ff00000) return x+x;       /* overflow  */
        if (ix <  0x00100000) {                 /* underflow */
                t = x*x;
                if (t != x) {                   /* raise underflow flag */
                        INSERT_WORDS(y, hx, lx);
                        return y;
                }
        }
        INSERT_WORDS(x, hx, lx);

        return x;
}