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mycroft
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/* $NetBSD: ldexp_040.c,v 1.1 1999/08/29 19:41:53 mycroft Exp $ */
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/* $NetBSD: ldexp_040.c,v 1.2 1999/08/29 19:42:54 mycroft Exp $ */
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/*-
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* Copyright (c) 1998 The NetBSD Foundation, Inc.
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* All rights reserved.
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/*
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* Copyright (c) 1992, 1993
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* The Regents of the University of California. 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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* This software was developed by the Computer Systems Engineering group
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* at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
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* contributed to Berkeley.
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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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@ -17,52 +18,135 @@
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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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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* 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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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* from: Header: ldexp.c,v 1.1 91/07/07 04:28:19 torek Exp
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*/
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#include <sys/cdefs.h>
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#if defined(LIBC_SCCS) && !defined(lint)
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__RCSID("$NetBSD: ldexp_040.c,v 1.1 1999/08/29 19:41:53 mycroft Exp $");
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#if 0
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static const char sccsid[] = "@(#)ldexp.c 8.1 (Berkeley) 6/4/93";
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#else
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__RCSID("$NetBSD: ldexp_040.c,v 1.2 1999/08/29 19:42:54 mycroft Exp $");
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#endif
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#endif /* LIBC_SCCS and not lint */
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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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* ldexp(value, exp): return value * (2 ** exp).
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* double ldexp(double val, int exp)
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* returns: val * (2**exp)
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*/
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double
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ldexp(value, exp)
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double value;
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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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double temp;
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register int oldexp, newexp, mulexp;
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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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#if __GNUC__ >= 2
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__asm ("fscale"
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: "=t" (temp)
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: "0" (value), "u" ((double)exp));
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#else
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__asm ("fscale; fstp %%st(1)"
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: "=f" (temp)
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: "f" (value), "0" ((double)exp));
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#endif
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return (temp);
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/*
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* If input is zero, or no change, just return input.
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* Likewise, if input is Inf or NaN, just return it.
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*/
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u.v = val;
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oldexp = u.s.dbl_exp;
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if (val == 0.0 || exp == 0 || oldexp == DBL_EXP_INFNAN)
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return (val);
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/*
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* Compute new exponent and check for over/under flow.
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* Underflow, unfortunately, could mean switching to denormal.
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* If result out of range, set ERANGE and return 0 if too small
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* or Inf if too big, with the same sign as the input value.
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*/
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newexp = oldexp + exp;
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if (newexp >= DBL_EXP_INFNAN) {
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/* u.s.dbl_sign = val < 0.0; -- already set */
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u.s.dbl_exp = DBL_EXP_INFNAN;
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u.s.dbl_frach = u.s.dbl_fracl = 0;
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errno = ERANGE;
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return (u.v); /* Inf */
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}
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if (newexp <= 0) {
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/*
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* The output number is either a denormal or underflows
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* (see 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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* We are going to produce a denorm. Our `exp' argument
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* might be as small as -2097, and we cannot compute
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* 2^-2097, so we may have to do this as many as three
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* steps (not just two, as for positive `exp's below).
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*/
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mul.v = 1.0;
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while (exp <= -DBL_EXP_BIAS) {
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mul.s.dbl_exp = 1;
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val *= mul.v;
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exp += DBL_EXP_BIAS - 1;
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}
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mul.s.dbl_exp = exp + DBL_EXP_BIAS;
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val *= mul.v;
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return (val);
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}
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/*
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* Newexp is positive.
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*
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* If oldexp is zero, we are starting with a denorm, and simply
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* adjusting the exponent will produce bogus answers. We need
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* to fix that first.
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*/
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if (oldexp == 0) {
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/*
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* Multiply by 2^mulexp to make the number normalizable.
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* We cannot multiply by more than 2^1023, but `exp'
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* argument might be as large as 2046. A single
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* adjustment, however, will normalize the number even
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* for huge `exp's, and then we can use exponent
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* arithmetic just as for normal `double's.
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*/
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mulexp = exp <= DBL_EXP_BIAS ? exp : DBL_EXP_BIAS;
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mul.v = 1.0;
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mul.s.dbl_exp = mulexp + DBL_EXP_BIAS;
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val *= mul.v;
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if (mulexp == exp)
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return (val);
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u.v = val;
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newexp -= mulexp;
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}
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/*
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* Both oldexp and newexp are positive; just replace the
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* old exponent with the 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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