136 lines
3.7 KiB
C
136 lines
3.7 KiB
C
/* $NetBSD: ldexp.c,v 1.1 1995/02/10 17:50:24 cgd Exp $ */
|
|
/* $FreeBSD$ */
|
|
|
|
/*
|
|
* 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/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);
|
|
}
|