156 lines
4.4 KiB
C
156 lines
4.4 KiB
C
/*-
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* Copyright (c) 1999 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Charles M. Hannum.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the NetBSD
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* Foundation, Inc. and its contributors.
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* 4. Neither the name of The NetBSD Foundation nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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#if 0
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#if defined(LIBC_SCCS) && !defined(lint)
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__RCSID("$NetBSD: ldexp.c,v 1.8 1999/08/30 18:28:26 mycroft Exp $");
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#endif /* LIBC_SCCS and not lint */
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#endif
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__FBSDID("$FreeBSD$");
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#include <sys/types.h>
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#include <machine/ieee.h>
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#include <errno.h>
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#include <math.h>
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/*
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* Multiply the given value by 2^exp.
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*/
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double
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ldexp(val, exp)
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double val;
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int exp;
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{
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int oldexp, newexp;
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union {
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double v;
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struct ieee_double s;
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} u, mul;
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u.v = val;
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oldexp = u.s.dbl_exp;
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/*
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* If input is zero, Inf or NaN, just return it.
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*/
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if (u.v == 0.0 || oldexp == DBL_EXP_INFNAN)
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return (val);
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if (oldexp == 0) {
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/*
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* u.v is denormal. We must adjust it so that the exponent
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* arithmetic below will work.
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*/
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if (exp <= DBL_EXP_BIAS) {
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/*
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* Optimization: if the scaling can be done in a single
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* multiply, or underflows, just do it now.
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*/
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if (exp <= -DBL_FRACBITS) {
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errno = ERANGE;
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return (0.0);
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}
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mul.v = 0.0;
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mul.s.dbl_exp = exp + DBL_EXP_BIAS;
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u.v *= mul.v;
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if (u.v == 0.0) {
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errno = ERANGE;
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return (0.0);
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}
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return (u.v);
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} else {
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/*
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* We know that exp is very large, and therefore the
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* result cannot be denormal (though it may be Inf).
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* Shift u.v by just enough to make it normal.
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*/
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mul.v = 0.0;
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mul.s.dbl_exp = DBL_FRACBITS + DBL_EXP_BIAS;
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u.v *= mul.v;
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exp -= DBL_FRACBITS;
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oldexp = u.s.dbl_exp;
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}
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}
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/*
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* u.v is now normalized and oldexp has been adjusted if necessary.
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* Calculate the new exponent and check for underflow and overflow.
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*/
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newexp = oldexp + exp;
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if (newexp <= 0) {
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/*
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* The output number is either denormal or underflows (see
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* comments in machine/ieee.h).
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*/
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if (newexp <= -DBL_FRACBITS) {
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errno = ERANGE;
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return (0.0);
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}
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/*
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* Denormalize the result. We do this with a multiply. If exp
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* is very large, it won't fit in a double, so we have to
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* adjust the exponent first. This is safe because we know
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* that u.v is normal at this point.
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*/
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if (exp <= -DBL_EXP_BIAS) {
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u.s.dbl_exp = 1;
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exp += oldexp - 1;
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}
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mul.v = 0.0;
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mul.s.dbl_exp = exp + DBL_EXP_BIAS;
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u.v *= mul.v;
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return (u.v);
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} else if (newexp >= DBL_EXP_INFNAN) {
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/*
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* The result overflowed; return +/-Inf.
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*/
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u.s.dbl_exp = DBL_EXP_INFNAN;
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u.s.dbl_frach = 0;
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u.s.dbl_fracl = 0;
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errno = ERANGE;
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return (u.v);
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} else {
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/*
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* The result is normal; just replace the old exponent with the
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* new one.
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*/
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u.s.dbl_exp = newexp;
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return (u.v);
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}
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}
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