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/* $OpenBSD: ldexp.c,v 1.2 2003/06/02 20:18:30 millert Exp $ */
/*
* Copyright (c) 1992, 1993
* The Regents of the University of California. All rights reserved.
*
* This software was developed by the Computer Systems Engineering group
* at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
* contributed to Berkeley.
*
* 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. Neither the name of the University 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 REGENTS 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 REGENTS 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.
*
* from: Header: ldexp.c,v 1.1 91/07/07 04:28:19 torek Exp
*/
#if defined(LIBC_SCCS) && !defined(lint)
static const char sccsid[] = "@(#)ldexp.c 8.1 (Berkeley) 6/4/93";
#endif /* LIBC_SCCS and not lint */
#include <sys/types.h>
#include <machine/ieee.h>
#include <errno.h>
/*
* double ldexp(double val, int exp)
* returns: val * (2**exp)
*/
double
ldexp(val, exp)
double val;
int exp;
{
register int oldexp, newexp, mulexp;
union doub {
double v;
struct ieee_double s;
} u, mul;
/*
* If input is zero, or no change, just return input.
* Likewise, if input is Inf or NaN, just return it.
*/
u.v = val;
oldexp = u.s.dbl_exp;
if (val == 0 || exp == 0 || oldexp == DBL_EXP_INFNAN)
return (val);
/*
* Compute new exponent and check for over/under flow.
* Underflow, unfortunately, could mean switching to denormal.
* If result out of range, set ERANGE and return 0 if too small
* or Inf if too big, with the same sign as the input value.
*/
newexp = oldexp + exp;
if (newexp >= DBL_EXP_INFNAN) {
/* u.s.dbl_sign = val < 0; -- already set */
u.s.dbl_exp = DBL_EXP_INFNAN;
u.s.dbl_frach = u.s.dbl_fracl = 0;
errno = ERANGE;
return (u.v); /* Inf */
}
if (newexp <= 0) {
/*
* The output number is either a denormal or underflows
* (see comments in machine/ieee.h).
*/
if (newexp <= -DBL_FRACBITS) {
/* u.s.dbl_sign = val < 0; -- already set */
u.s.dbl_exp = 0;
u.s.dbl_frach = u.s.dbl_fracl = 0;
errno = ERANGE;
return (u.v); /* zero */
}
/*
* We are going to produce a denorm. Our `exp' argument
* might be as small as -2097, and we cannot compute
* 2^-2097, so we may have to do this as many as three
* steps (not just two, as for positive `exp's below).
*/
mul.v = 0;
while (exp <= -DBL_EXP_BIAS) {
mul.s.dbl_exp = 1;
val *= mul.v;
exp += DBL_EXP_BIAS - 1;
}
mul.s.dbl_exp = exp + DBL_EXP_BIAS;
val *= mul.v;
return (val);
}
/*
* Newexp is positive.
*
* If oldexp is zero, we are starting with a denorm, and simply
* adjusting the exponent will produce bogus answers. We need
* to fix that first.
*/
if (oldexp == 0) {
/*
* Multiply by 2^mulexp to make the number normalizable.
* We cannot multiply by more than 2^1023, but `exp'
* argument might be as large as 2046. A single
* adjustment, however, will normalize the number even
* for huge `exp's, and then we can use exponent
* arithmetic just as for normal `double's.
*/
mulexp = exp <= DBL_EXP_BIAS ? exp : DBL_EXP_BIAS;
mul.v = 0;
mul.s.dbl_exp = mulexp + DBL_EXP_BIAS;
val *= mul.v;
if (mulexp == exp)
return (val);
u.v = val;
newexp -= mulexp;
}
/*
* Both oldexp and newexp are positive; just replace the
* old exponent with the new one.
*/
u.s.dbl_exp = newexp;
return (u.v);
}
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