mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-18 02:50:09 +00:00
a5707dad25
2000-06-29 Ulrich Drepper <drepper@redhat.com> * stdio-common/printf_fp.c (__printf_fp): Don't clobber pointer which we later need to calling free(). Patch by Matt Wilson <msw@redhat.com>. 2000-06-27 David Mosberger-Tang <davidm@hpl.hp.com> * sysdeps/unix/sysv/linux/ia64/bits/ipc.h: New file. * sysdeps/unix/sysv/linux/ia64/bits/shm.h: New file. 2000-06-28 Jes Sorensen <jes@linuxcare.com> * sysdeps/ieee754/dbl-64/s_exp2.c: Add include stdlib.h to get prototype for abs(). * sysdeps/ieee754/flt-32/s_exp2f.c: ditto.
129 lines
3.9 KiB
C
129 lines
3.9 KiB
C
/* Single-precision floating point 2^x.
|
|
Copyright (C) 1997, 1998, 2000 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
Contributed by Geoffrey Keating <geoffk@ozemail.com.au>
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Library General Public License as
|
|
published by the Free Software Foundation; either version 2 of the
|
|
License, or (at your option) any later version.
|
|
|
|
The GNU C Library is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Library General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Library General Public
|
|
License along with the GNU C Library; see the file COPYING.LIB. If not,
|
|
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
|
|
Boston, MA 02111-1307, USA. */
|
|
|
|
/* The basic design here is from
|
|
Shmuel Gal and Boris Bachelis, "An Accurate Elementary Mathematical
|
|
Library for the IEEE Floating Point Standard", ACM Trans. Math. Soft.,
|
|
17 (1), March 1991, pp. 26-45.
|
|
It has been slightly modified to compute 2^x instead of e^x, and for
|
|
single-precision.
|
|
*/
|
|
#ifndef _GNU_SOURCE
|
|
# define _GNU_SOURCE
|
|
#endif
|
|
#include <stdlib.h>
|
|
#include <float.h>
|
|
#include <ieee754.h>
|
|
#include <math.h>
|
|
#include <fenv.h>
|
|
#include <inttypes.h>
|
|
#include <math_private.h>
|
|
|
|
#include "t_exp2f.h"
|
|
|
|
static const volatile float TWOM100 = 7.88860905e-31;
|
|
static const volatile float TWO127 = 1.7014118346e+38;
|
|
|
|
float
|
|
__ieee754_exp2f (float x)
|
|
{
|
|
static const float himark = (float) FLT_MAX_EXP;
|
|
static const float lomark = (float) (FLT_MIN_EXP - FLT_MANT_DIG - 1) - 1.0;
|
|
|
|
/* Check for usual case. */
|
|
if (isless (x, himark) && isgreater (x, lomark))
|
|
{
|
|
static const float THREEp14 = 49152.0;
|
|
int tval, unsafe;
|
|
float rx, x22, result;
|
|
union ieee754_float ex2_u, scale_u;
|
|
fenv_t oldenv;
|
|
|
|
feholdexcept (&oldenv);
|
|
#ifdef FE_TONEAREST
|
|
/* If we don't have this, it's too bad. */
|
|
fesetround (FE_TONEAREST);
|
|
#endif
|
|
|
|
/* 1. Argument reduction.
|
|
Choose integers ex, -128 <= t < 128, and some real
|
|
-1/512 <= x1 <= 1/512 so that
|
|
x = ex + t/512 + x1.
|
|
|
|
First, calculate rx = ex + t/256. */
|
|
rx = x + THREEp14;
|
|
rx -= THREEp14;
|
|
x -= rx; /* Compute x=x1. */
|
|
/* Compute tval = (ex*256 + t)+128.
|
|
Now, t = (tval mod 256)-128 and ex=tval/256 [that's mod, NOT %; and
|
|
/-round-to-nearest not the usual c integer /]. */
|
|
tval = (int) (rx * 256.0f + 128.0f);
|
|
|
|
/* 2. Adjust for accurate table entry.
|
|
Find e so that
|
|
x = ex + t/256 + e + x2
|
|
where -7e-4 < e < 7e-4, and
|
|
(float)(2^(t/256+e))
|
|
is accurate to one part in 2^-64. */
|
|
|
|
/* 'tval & 255' is the same as 'tval%256' except that it's always
|
|
positive.
|
|
Compute x = x2. */
|
|
x -= __exp2f_deltatable[tval & 255];
|
|
|
|
/* 3. Compute ex2 = 2^(t/255+e+ex). */
|
|
ex2_u.f = __exp2f_atable[tval & 255];
|
|
tval >>= 8;
|
|
unsafe = abs(tval) >= -FLT_MIN_EXP - 1;
|
|
ex2_u.ieee.exponent += tval >> unsafe;
|
|
scale_u.f = 1.0;
|
|
scale_u.ieee.exponent += tval - (tval >> unsafe);
|
|
|
|
/* 4. Approximate 2^x2 - 1, using a second-degree polynomial,
|
|
with maximum error in [-2^-9 - 2^-14, 2^-9 + 2^-14]
|
|
less than 1.3e-10. */
|
|
|
|
x22 = (.24022656679f * x + .69314736128f) * ex2_u.f;
|
|
|
|
/* 5. Return (2^x2-1) * 2^(t/512+e+ex) + 2^(t/512+e+ex). */
|
|
fesetenv (&oldenv);
|
|
|
|
result = x22 * x + ex2_u.f;
|
|
|
|
if (!unsafe)
|
|
return result;
|
|
else
|
|
return result * scale_u.f;
|
|
}
|
|
/* Exceptional cases: */
|
|
else if (isless (x, himark))
|
|
{
|
|
if (__isinff (x))
|
|
/* e^-inf == 0, with no error. */
|
|
return 0;
|
|
else
|
|
/* Underflow */
|
|
return TWOM100 * TWOM100;
|
|
}
|
|
else
|
|
/* Return x, if x is a NaN or Inf; or overflow, otherwise. */
|
|
return TWO127*x;
|
|
}
|