ack/lang/cem/libcc.ansi/math/ldexp.c

/*
 * (c) copyright 1987 by the Vrije Universiteit, Amsterdam, The Netherlands.
 * See the copyright notice in the ACK home directory, in the file "Copyright".
 */
/* $Id$ */

#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;
}