ldexp(denormal, exp>1023) would generate the wrong result in all non-overflow
cases. Totally rework this code to fix this bug *and* make it faster.
This commit is contained in:
mycroft
parent
7a3bd0ab27
commit
6b221be206
|
|
@ -1,12 +1,11 @@
|
|||
/* $NetBSD: ldexp_040.c,v 1.2 1999/08/29 19:42:54 mycroft Exp $ */
|
||||
/* $NetBSD: ldexp_040.c,v 1.3 1999/08/29 22:50:25 mycroft Exp $ */
|
||||
|
||||
/*
|
||||
* Copyright (c) 1992, 1993
|
||||
* The Regents of the University of California. All rights reserved.
|
||||
/*-
|
||||
* Copyright (c) 1999 The NetBSD Foundation, Inc.
|
||||
* 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.
|
||||
* 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
|
||||
|
|
@ -18,34 +17,28 @@
|
|||
* 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 University of
|
||||
* California, Berkeley and its contributors.
|
||||
* 4. 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 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 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
|
||||
* 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>
|
||||
#if defined(LIBC_SCCS) && !defined(lint)
|
||||
#if 0
|
||||
static const char sccsid[] = "@(#)ldexp.c 8.1 (Berkeley) 6/4/93";
|
||||
#else
|
||||
__RCSID("$NetBSD: ldexp_040.c,v 1.2 1999/08/29 19:42:54 mycroft Exp $");
|
||||
#endif
|
||||
__RCSID("$NetBSD: ldexp_040.c,v 1.3 1999/08/29 22:50:25 mycroft Exp $");
|
||||
#endif /* LIBC_SCCS and not lint */
|
||||
|
||||
#include <sys/types.h>
|
||||
|
|
@ -54,8 +47,7 @@ __RCSID("$NetBSD: ldexp_040.c,v 1.2 1999/08/29 19:42:54 mycroft Exp $");
|
|||
#include <math.h>
|
||||
|
||||
/*
|
||||
* double ldexp(double val, int exp)
|
||||
* returns: val * (2**exp)
|
||||
* Multiply the given value by 2^exp.
|
||||
*/
|
||||
double
|
||||
ldexp(val, exp)
|
||||
|
|
@ -68,85 +60,95 @@ ldexp(val, exp)
|
|||
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 == 0.0 || 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.
|
||||
* 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 (exp <= DBL_EXP_BIAS) {
|
||||
/*
|
||||
* Optimization: if the scaling can be done in a single
|
||||
* multiply, or underflows, just do it now.
|
||||
*/
|
||||
if (exp <= -DBL_FRACBITS) {
|
||||
errno = ERANGE;
|
||||
return (0.0);
|
||||
}
|
||||
mul.v = 1.0;
|
||||
mul.s.dbl_exp = exp + DBL_EXP_BIAS;
|
||||
u.v *= mul.v;
|
||||
if (u.v == 0.0) {
|
||||
errno = ERANGE;
|
||||
return (0.0);
|
||||
}
|
||||
return (u.v);
|
||||
} else {
|
||||
/*
|
||||
* We know that exp 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 = 1.0;
|
||||
mul.s.dbl_exp = DBL_FRACBITS + DBL_EXP_BIAS;
|
||||
u.v *= mul.v;
|
||||
exp -= 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 + exp;
|
||||
|
||||
if (newexp >= DBL_EXP_INFNAN) {
|
||||
/* u.s.dbl_sign = val < 0.0; -- 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).
|
||||
* 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 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);
|
||||
}
|
||||
/*
|
||||
* 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).
|
||||
* Denormalize the result. We do this with a multiply. If exp
|
||||
* 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.
|
||||
*/
|
||||
mul.v = 1.0;
|
||||
while (exp <= -DBL_EXP_BIAS) {
|
||||
mul.s.dbl_exp = 1;
|
||||
val *= mul.v;
|
||||
exp += DBL_EXP_BIAS - 1;
|
||||
if (exp <= -DBL_EXP_BIAS) {
|
||||
u.s.dbl_exp = 1;
|
||||
exp += oldexp - 1;
|
||||
}
|
||||
mul.v = 1.0;
|
||||
mul.s.dbl_exp = exp + DBL_EXP_BIAS;
|
||||
val *= mul.v;
|
||||
return (val);
|
||||
}
|
||||
|
||||
u.v *= mul.v;
|
||||
return (u.v);
|
||||
} else {
|
||||
/*
|
||||
* 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 = 1.0;
|
||||
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.
|
||||
* The result is normal; just replace the old exponent with the
|
||||
* new one.
|
||||
*/
|
||||
u.s.dbl_exp = newexp;
|
||||
return (u.v);
|
||||
}
|
||||
}
|
||||
|
|
|
|||
Loading…
Reference in New Issue