source: trunk/minix/lib/ack/math/ldexp.c@ 9

/*
 * (c) copyright 1987 by the Vrije Universiteit, Amsterdam, The Netherlands.
 * See the copyright notice in the ACK home directory, in the file "Copyright".
 */
/* $Header: /cvsup/minix/src/lib/ack/math/ldexp.c,v 1.1 2005/10/10 15:27:47 beng Exp $ */

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

double
ldexp(double fl, int exp)
{
        int sign = 1;
        int currexp;

        if (__IsNan(fl)) {
                errno = EDOM;
                return fl;
        }
        if (fl == 0.0) return 0.0;
        if (fl<0) {
                fl = -fl;
                sign = -1;
        }
        if (fl > DBL_MAX) {             /* for infinity */
                errno = ERANGE;
                return sign * fl;
        }
        fl = frexp(fl,&currexp);
        exp += currexp;
        if (exp > 0) {
                if (exp > DBL_MAX_EXP) {
                        errno = ERANGE;
                        return sign * HUGE_VAL;
                }
                while (exp>30) {
                        fl *= (double) (1L << 30);
                        exp -= 30;
                }
                fl *= (double) (1L << exp);
        }
        else    {
                /* number need not be normalized */
                if (exp < DBL_MIN_EXP - DBL_MANT_DIG) {
                        return 0.0;
                }
                while (exp<-30) {
                        fl /= (double) (1L << 30);
                        exp += 30;
                }
                fl /= (double) (1L << -exp);
        }
        return sign * fl;
}