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

/* @(#)s_scalbn.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.
 * ====================================================
 */

#ifndef lint
static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_scalbnl.c,v 1.1 2005/03/07 04:52:58 das Exp $";
#endif

/*
 * scalbnl (long double x, int n)
 * scalbnl(x,n) returns x* 2**n  computed by  exponent
 * manipulation rather than by actually performing an
 * exponentiation or a multiplication.
 */

/*
 * We assume that a long double has a 15-bit exponent.  On systems
 * where long double is the same as double, scalbnl() is an alias
 * for scalbn(), so we don't use this routine.
 */

#include <sys/cdefs.h>
#include <float.h>
#include <math.h>

#include "fpmath.h"

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

static const long double
huge = 0x1p16000L,
tiny = 0x1p-16000L;

long double
scalbnl (long double x, int n)
{
        union IEEEl2bits u;
        int k;
        u.e = x;
        k = u.bits.exp;                         /* extract exponent */
        if (k==0) {                             /* 0 or subnormal x */
            if ((u.bits.manh|u.bits.manl)==0) return x; /* +-0 */
            u.e *= 0x1p+128;
            k = u.bits.exp - 128;
            if (n< -50000) return tiny*x;       /*underflow*/
            }
        if (k==0x7fff) return x+x;              /* NaN or Inf */
        k = k+n;
        if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow  */
        if (k > 0)                              /* normal result */
            {u.bits.exp = k; return u.e;}
        if (k <= -128)
            if (n > 50000)      /* in case integer overflow in n+k */
                return huge*copysign(huge,x);   /*overflow*/
            else return tiny*copysign(tiny,x);  /*underflow*/
        k += 128;                               /* subnormal result */
        u.bits.exp = k;
        return u.e*0x1p-128;
}

__strong_reference(scalbnl, ldexpl);