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Replace the ldexp() implementation in libc with a renamed copy of the

Browse Source 
scalbn() implementation from libm.  (The two functions are defined to
be identical, but ldexp() lives in libc for backwards compatibility.)
The old ldexp() implementation...
  - was more complicated than this one
  - set errno instead of raising FP exceptions
  - got some corner cases wrong
    (e.g. ldexp(1.0, 2000) in round-to-zero mode)

The new implementation lives in libc/gen instead of
libc/$MACHINE_ARCH/gen, since we don't need N copies of a
machine-independent file.  The amd64 and i386 platforms
retain their fast and correct MD implementations and
override this one.
This commit is contained in:
David Schultz 2005-01-22 06:03:40 +00:00
parent 4d28b4d206
commit 00646ca204
6 changed files with 123 additions and 739 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

137
lib/libc/alpha/gen/ldexp.c
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@ -1,137 +0,0 @@
/*
* Copyright (c) 1994, 1995 Carnegie-Mellon University.
* All rights reserved.
*
* Author: Chris G. Demetriou
*
* Permission to use, copy, modify and distribute this software and
* its documentation is hereby granted, provided that both the copyright
* notice and this permission notice appear in all copies of the
* software, derivative works or modified versions, and any portions
* thereof, and that both notices appear in supporting documentation.
*
* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
* FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
*
* Carnegie Mellon requests users of this software to return to
*
* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
* School of Computer Science
* Carnegie Mellon University
* Pittsburgh PA 15213-3890
*
* any improvements or extensions that they make and grant Carnegie the
* rights to redistribute these changes.
*
* $NetBSD: ldexp.c,v 1.1 1995/02/10 17:50:24 cgd Exp $
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <machine/ieee.h>
#include <errno.h>
#include <math.h>
/*
* double ldexp(double val, int exp)
* returns: val * (2**exp)
*/
double
ldexp(val, exp)
double val;
int exp;
{
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);
}

155
lib/libc/arm/gen/ldexp.c
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@ -1,155 +0,0 @@
/*-
* 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>
#if 0
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: ldexp.c,v 1.8 1999/08/30 18:28:26 mycroft Exp $");
#endif /* LIBC_SCCS and not lint */
#endif
__FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <errno.h>
#include <math.h>
#include <machine/ieee.h>
/*
* Multiply the given value by 2^exp.
*/
double
ldexp(val, exp)
double val;
int exp;
{
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 (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 = 0.0;
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 = 0.0;
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 <= 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 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.
*/
if (exp <= -DBL_EXP_BIAS) {
u.s.dbl_exp = 1;
exp += oldexp - 1;
}
mul.v = 0.0;
mul.s.dbl_exp = exp + 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);
}
}

123
lib/libc/gen/ldexp.c Normal file
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@ -0,0 +1,123 @@
/* @(#)s_scalbn.c 5.1 93/09/24 */
/* @(#)fdlibm.h 5.1 93/09/24 */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <machine/endian.h>
#include <math.h>
/* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
#if BYTE_ORDER == BIG_ENDIAN
typedef union
{
double value;
struct
{
u_int32_t msw;
u_int32_t lsw;
} parts;
} ieee_double_shape_type;
#endif
#if BYTE_ORDER == LITTLE_ENDIAN
typedef union
{
double value;
struct
{
u_int32_t lsw;
u_int32_t msw;
} parts;
} ieee_double_shape_type;
#endif
/* Get two 32 bit ints from a double. */
#define EXTRACT_WORDS(ix0,ix1,d) \
do { \
ieee_double_shape_type ew_u; \
ew_u.value = (d); \
(ix0) = ew_u.parts.msw; \
(ix1) = ew_u.parts.lsw; \
} while (0)
/* Get the more significant 32 bit int from a double. */
#define GET_HIGH_WORD(i,d) \
do { \
ieee_double_shape_type gh_u; \
gh_u.value = (d); \
(i) = gh_u.parts.msw; \
} while (0)
/* Set the more significant 32 bits of a double from an int. */
#define SET_HIGH_WORD(d,v) \
do { \
ieee_double_shape_type sh_u; \
sh_u.value = (d); \
sh_u.parts.msw = (v); \
(d) = sh_u.value; \
} while (0)
static const double
two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
huge = 1.0e+300,
tiny = 1.0e-300;
static double
_copysign(double x, double y)
{
u_int32_t hx,hy;
GET_HIGH_WORD(hx,x);
GET_HIGH_WORD(hy,y);
SET_HIGH_WORD(x,(hx&0x7fffffff)|(hy&0x80000000));
return x;
}
double
ldexp(double x, int n)
{
int32_t k,hx,lx;
EXTRACT_WORDS(hx,lx,x);
k = (hx&0x7ff00000)>>20; /* extract exponent */
if (k==0) { /* 0 or subnormal x */
if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
x *= two54;
GET_HIGH_WORD(hx,x);
k = ((hx&0x7ff00000)>>20) - 54;
if (n< -50000) return tiny*x; /*underflow*/
}
if (k==0x7ff) return x+x; /* NaN or Inf */
k = k+n;
if (k > 0x7fe) return huge*_copysign(huge,x); /* overflow */
if (k > 0) /* normal result */
{SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
if (k <= -54) {
if (n > 50000) /* in case integer overflow in n+k */
return huge*_copysign(huge,x); /*overflow*/
else return tiny*_copysign(tiny,x); /*underflow*/
}
k += 54; /* subnormal result */
SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
return x*twom54;
}

137
lib/libc/ia64/gen/ldexp.c
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@ -1,137 +0,0 @@
/* $NetBSD: ldexp.c,v 1.1 1995/02/10 17:50:24 cgd Exp $ */
/*
* Copyright (c) 1994, 1995 Carnegie-Mellon University.
* All rights reserved.
*
* Author: Chris G. Demetriou
*
* Permission to use, copy, modify and distribute this software and
* its documentation is hereby granted, provided that both the copyright
* notice and this permission notice appear in all copies of the
* software, derivative works or modified versions, and any portions
* thereof, and that both notices appear in supporting documentation.
*
* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
* FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
*
* Carnegie Mellon requests users of this software to return to
*
* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
* School of Computer Science
* Carnegie Mellon University
* Pittsburgh PA 15213-3890
*
* any improvements or extensions that they make and grant Carnegie the
* rights to redistribute these changes.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <machine/ieee.h>
#include <errno.h>
#include <math.h>
/*
* double ldexp(double val, int exp)
* returns: val * (2**exp)
*/
double
ldexp(val, exp)
double val;
int exp;
{
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);
}

155
lib/libc/powerpc/gen/ldexp.c
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@ -1,155 +0,0 @@
/*-
* 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>
#if 0
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: ldexp.c,v 1.8 1999/08/30 18:28:26 mycroft Exp $");
#endif /* LIBC_SCCS and not lint */
#endif
__FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <machine/ieee.h>
#include <errno.h>
#include <math.h>
/*
* Multiply the given value by 2^exp.
*/
double
ldexp(val, exp)
double val;
int exp;
{
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 (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 = 0.0;
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 = 0.0;
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 <= 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 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.
*/
if (exp <= -DBL_EXP_BIAS) {
u.s.dbl_exp = 1;
exp += oldexp - 1;
}
mul.v = 0.0;
mul.s.dbl_exp = exp + 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);
}
}

155
lib/libc/sparc64/gen/ldexp.c
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@ -1,155 +0,0 @@
/*-
* 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>
#if 0
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: ldexp.c,v 1.8 1999/08/30 18:28:26 mycroft Exp $");
#endif /* LIBC_SCCS and not lint */
#endif
__FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <machine/ieee.h>
#include <errno.h>
#include <math.h>
/*
* Multiply the given value by 2^exp.
*/
double
ldexp(val, exp)
double val;
int exp;
{
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 (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 = 0.0;
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 = 0.0;
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 <= 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 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.
*/
if (exp <= -DBL_EXP_BIAS) {
u.s.dbl_exp = 1;
exp += oldexp - 1;
}
mul.v = 0.0;
mul.s.dbl_exp = exp + 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);
}
}