xref: /titanic_52/usr/src/lib/libbc/libc/gen/common/ldexp.c (revision 7c478bd95313f5f23a4c958a745db2134aa03244)

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 1988 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*      Copyright (c) 1984 AT&T */
/*        All Rights Reserved   */

#pragma ident	"%Z%%M%	%I%	%E% SMI"  /* from S5R2 2.7 */

/*LINTLIBRARY*/
/*
 *	double ldexp (value, exp)
 *		double value;
 *		int exp;
 *
 *	Ldexp returns value * 2**exp, if that result is in range.
 *	If underflow occurs, it returns zero.  If overflow occurs,
 *	it returns a value of appropriate sign and largest single-
 *	precision magnitude.  In case of underflow or overflow,
 *	the external int "errno" is set to ERANGE.  Note that errno is
 *	not modified if no error occurs, so if you intend to test it
 *	after you use ldexp, you had better set it to something
 *	other than ERANGE first (zero is a reasonable value to use).
 */

#include <values.h>
#include <errno.h>
/* Largest signed long int power of 2 */
#define MAXSHIFT	(BITSPERBYTE * sizeof(long) - 2)

extern double frexp();

double
ldexp(value, exp)
register double value;
register int exp;
{
	int old_exp;

	if (exp == 0 || value == 0.0) /* nothing to do for zero */
		return (value);
#if	!(pdp11 || u3b5)	/* pdp11 "cc" can't handle cast of
				   double to void on pdp11 or 3b5 */
	(void)
#endif
	frexp(value, &old_exp);
	if (exp > 0) {
		if (exp + old_exp > MAXBEXP) { /* overflow */
			errno = ERANGE;
			return ((double)(value < 0 ? MINDOUBLE : MAXDOUBLE));
/*
			return ((double)(value < 0 ? -1.0e999 : 1.0e999));
*/
		}
		for ( ; exp > MAXSHIFT; exp -= MAXSHIFT)
			value *= (1L << MAXSHIFT);
		return (value * (1L << exp));
	}
	if (exp + old_exp < MINBEXP) { /* underflow */
		errno = ERANGE;
		return (0.0);
	}
	for ( ; exp < -MAXSHIFT; exp += MAXSHIFT)
		value *= 1.0/(1L << MAXSHIFT); /* mult faster than div */
	return (value / (1L << -exp));
}