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pow(double, int)
- To: "libstdc++ at sourceware dot cygnus dot com" <libstdc++ at sourceware dot cygnus dot com>
- Subject: pow(double, int)
- From: Petter Urkedal <petter at matfys dot lth dot se>
- Date: Wed, 05 Apr 2000 01:02:34 +0200
I resurrected an pow(*, int) code for use in libstdc++, unless someone
has an even faster one lying around. As seen from the benchmark it
improves
performance, especially for small exponents, but also gives 2x for large
exponents.
I was confused by the headers; `shadow/bits/std_cmath.h' is meant
to become a _replacement_ for `bits/std_cmath.h', right?
Cheers,
-petter.
2000-04-05 Petter Urkedal <petter@matfys.lth.se>
* src/cmath.cc: New file...
(pow(*, int)): Define functions...
* src/Makefile.am (sources): ...register file.
* src/Makefile.in: Regenerate.
* bits/std_cmath.h (pow): ...declare functions here, and remove
old definitions.
Testing float versions:
pow( -0.505, 1): 0.04 s 0.4 s
pow( -0.504005, -1): 0.06 s 0.39 s
pow( -0.462953, 10): 0.08 s 0.39 s
pow( -0.326591, -10): 0.09 s 0.43 s
pow( -0.136752, 100): 0.32 s 0.65 s
pow( -0.412756, -100): 0.11 s 0.45 s
pow( -0.411779, 1000): 0.36 s 0.83 s
pow(-0.0129106, -1000): 0.17 s 0.8 s
pow( 0.0270178, 10000): 0.41 s 0.91 s
pow(-0.0460222, -10000): 0.45 s 0.85 s
pow( -0.26949, 100000): 0.46 s 1.01 s
pow( 0.334605, -100000): 0.46 s 0.91 s
pow( 0.436049, 1000000): 0.53 s 1.07 s
pow( 0.0687402, -1000000): 0.58 s 1.01 s
pow( 0.0566553, 10000000): 0.68 s 1.26 s
pow( -0.45366, -10000000): 0.7 s 1.19 s
pow( 0.269722, 100000000): 0.63 s 1.28 s
pow( -0.485896,-100000000): 0.7 s 1.22 s
pow( -0.250117,1000000000): 0.73 s 1.37 s
pow( -0.203821,-1000000000): 0.74 s 1.15 s
pow( 0.379741,-2147483648): 0.56 s 0.93 s
pow( 0.0318724,-2147483648): 0.58 s 0.94 s
Check if they agree at the singularity:
pow(0.0, 0) = 1
pow(0.0, 0.0) = 1
Testing double versions:
pow( 0.424464, 1): 0.07 s 0.35 s
pow( 0.0155855, -1): 0.11 s 0.36 s
pow( 0.313534, 10): 0.11 s 0.37 s
pow( -0.314696, -10): 0.14 s 0.39 s
pow( 0.390178, 100): 0.13 s 0.42 s
pow( 0.0713202, -100): 0.21 s 0.42 s
pow( -0.427458, 1000): 0.37 s 0.81 s
pow( 0.318427, -1000): 0.2 s 0.68 s
pow( 0.48974, 10000): 0.39 s 1.05 s
pow( -0.385465, -10000): 0.26 s 0.8 s
pow( 0.397845, 100000): 0.49 s 1.04 s
pow( 0.287328, -100000): 0.56 s 0.88 s
pow( -0.403075, 1000000): 0.62 s 1.13 s
pow( -0.249156, -1000000): 0.8 s 1.02 s
pow( -0.48496, 10000000): 0.7 s 1.21 s
pow( -0.122839, -10000000): 0.97 s 1.13 s
pow( 0.180666, 100000000): 0.68 s 1.14 s
pow( 0.182732,-100000000): 0.67 s 0.99 s
pow( 0.255234,1000000000): 0.69 s 1.21 s
pow( -0.498708,-1000000000): 1.09 s 1.15 s
pow( 0.125651,-2147483648): 0.58 s 0.9 s
pow( -0.377273,-2147483648): 0.58 s 0.96 s
Check if they agree at the singularity:
pow(0.0, 0) = 1
pow(0.0, 0.0) = 1
// -*- C++ -*- C math library.
// Copyright (C) 1997, 1998, 1999, 2000 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.
// This 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 General Public License for more details.
// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING. If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.
// As a special exception, you may use this file as part of a free software
// library without restriction. Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License. This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.
//
// ISO C++ 14882: 26.5 C library
// Code for signatures not found in the C library
//
#include <bits/std_cmath.h>
namespace std
{
namespace {
template <typename T>
inline T pow_helper(T x, unsigned int y)
{
T z = y&1? x : 1;
while(y >>= 1)
{
x *= x;
if(y & 1) z *= x;
}
return z;
}
}
float
pow(float x, int y)
{
if(y < 0)
return 1.0f/pow_helper(x, -y);
else
return pow_helper(x, y);
}
double
pow(double x, int y)
{
if(y < 0)
return 1.0/pow_helper(x, -y);
else
return pow_helper(x, y);
}
long double
pow(long double x, int y)
{
if(y < 0)
return 1.0l/pow_helper(x, -y);
else
return pow_helper(x, y);
}
}
Index: bits/std_cmath.h
===================================================================
RCS file: /cvs/libstdc++/libstdc++/bits/std_cmath.h,v
retrieving revision 1.18
diff -c -r1.18 std_cmath.h
*** std_cmath.h 2000/03/21 06:24:04 1.18
--- std_cmath.h 2000/04/04 23:03:10
***************
*** 52,59 ****
inline double
abs(double __x) { return ::fabs(__x); }
! inline double
! pow(double __x, int __i) { return ::pow(__x, static_cast<double>(__i)); }
// float
inline float
--- 52,59 ----
inline double
abs(double __x) { return ::fabs(__x); }
! double
! pow(double, int);
// float
inline float
***************
*** 78,86 ****
pow(float __x, float __y)
{ return ::pow(static_cast<double>(__x), static_cast<double>(__y)); }
! inline float
! pow(float __x, int __i)
! { return ::pow(static_cast<double>(__x), static_cast<double>(__i)); }
#if _GLIBCPP_HAVE_ABSF
inline float
--- 78,85 ----
pow(float __x, float __y)
{ return ::pow(static_cast<double>(__x), static_cast<double>(__y)); }
! float
! pow(float, int);
#if _GLIBCPP_HAVE_ABSF
inline float
***************
*** 239,244 ****
--- 238,246 ----
// XXX long double
+
+ long double
+ pow(long double, int);
} // std
bench_cmath.tgz