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/* $OpenBSD: ldexp.c,v 1.2 2004/02/01 05:40:52 drahn Exp $ */
/* $NetBSD: ldexp.c,v 1.2 2001/11/08 22:45:45 bjh21 Exp $ */
/*-
* Copyright (c) 1999 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Charles M. Hannum.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the NetBSD
* Foundation, Inc. and its contributors.
* 4. Neither the name of The NetBSD Foundation nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/cdefs.h>
#include <sys/types.h>
#include <machine/ieee.h>
#include <errno.h>
#include <math.h>
/*
* Multiply the given value by 2^exponent.
*/
double
ldexp(val, expo)
double val;
int expo;
{
register int oldexp, newexp;
union {
double v;
struct ieee_double s;
} u, mul;
u.v = val;
oldexp = u.s.dbl_exp;
/*
* If input is zero, Inf or NaN, just return it.
*/
if (u.v == 0.0 || oldexp == DBL_EXP_INFNAN)
return (val);
if (oldexp == 0) {
/*
* u.v is denormal. We must adjust it so that the exponent
* arithmetic below will work.
*/
if (expo <= DBL_EXP_BIAS) {
/*
* Optimization: if the scaling can be done in a single
* multiply, or underflows, just do it now.
*/
if (expo <= -DBL_FRACBITS) {
errno = ERANGE;
return (0.0);
}
mul.v = 0.0;
mul.s.dbl_exp = expo + DBL_EXP_BIAS;
u.v *= mul.v;
if (u.v == 0.0) {
errno = ERANGE;
return (0.0);
}
return (u.v);
} else {
/*
* We know that expo is very large, and therefore the
* result cannot be denormal (though it may be Inf).
* Shift u.v by just enough to make it normal.
*/
mul.v = 0.0;
mul.s.dbl_exp = DBL_FRACBITS + DBL_EXP_BIAS;
u.v *= mul.v;
expo -= DBL_FRACBITS;
oldexp = u.s.dbl_exp;
}
}
/*
* u.v is now normalized and oldexp has been adjusted if necessary.
* Calculate the new exponent and check for underflow and overflow.
*/
newexp = oldexp + expo;
if (newexp <= 0) {
/*
* The output number is either denormal or underflows (see
* comments in machine/ieee.h).
*/
if (newexp <= -DBL_FRACBITS) {
errno = ERANGE;
return (0.0);
}
/*
* Denormalize the result. We do this with a multiply. If expo
* is very large, it won't fit in a double, so we have to
* adjust the exponent first. This is safe because we know
* that u.v is normal at this point.
*/
if (expo <= -DBL_EXP_BIAS) {
u.s.dbl_exp = 1;
expo += oldexp - 1;
}
mul.v = 0.0;
mul.s.dbl_exp = expo + DBL_EXP_BIAS;
u.v *= mul.v;
return (u.v);
} else if (newexp >= DBL_EXP_INFNAN) {
/*
* The result overflowed; return +/-Inf.
*/
u.s.dbl_exp = DBL_EXP_INFNAN;
u.s.dbl_frach = 0;
u.s.dbl_fracl = 0;
errno = ERANGE;
return (u.v);
} else {
/*
* The result is normal; just replace the old exponent with the
* new one.
*/
u.s.dbl_exp = newexp;
return (u.v);
}
}
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