From: "(see below)" <yaldnif.w@blueyonder.co.uk>
Subject: Re: Is there an Ada compiler whose Ada.Numerics.Generic_Elementary_Functions.Log(Base=>10, X=>variable) is efficient?
Date: Mon, 15 Feb 2010 18:26:31 +0000
Date: 2010-02-15T18:26:31+00:00 [thread overview]
Message-ID: <C79F4257.1365BE%yaldnif.w@blueyonder.co.uk> (raw)
In-Reply-To: alpine.LNX.2.00.1002151055530.17315@Bluewhite64.example.net
On 15/02/2010 10:58, in article
alpine.LNX.2.00.1002151055530.17315@Bluewhite64.example.net, "Colin Paul
Gloster" <Colin_Paul_Gloster@ACM.org> wrote:
> Of the two programs shown, the fastest C++ implementation on one test
> platform took less than one millisecond and the fastest Ada
> implementation took one minute and 31 seconds and 874 milliseconds on
> the same platform. Both g++ and gnatmake were from the same
> installation of GCC 4.1.2 20080704 (Red Hat 4.1.2-44).
Is that 1 millisecond for 1e6 calls? This implies 1ns per call in C++.
I find it incredible that a log function could be so fast.
I think the loop body must be evaluated at compile-time in C++.
On my system your Ada code gives:
6.34086408536266E+08
real 0m33.918s
user 0m33.864s
sys 0m0.025s
And your original C++ code gives:
6.34086e+08
real 0m0.110s
user 0m0.003s
sys 0m0.003s
But if I replace the C++ loop body by:
for(int j=1; j<=500; ++j)
answer += std::log10(j*0.100000000000000000000);
It now gives:
6.34086e+08
real 0m18.112s
user 0m18.082s
sys 0m0.015s
This less than twice as fast as the more generalized Ada code.
The simpler inner loop:
for(int j=1; j<=500; ++j)
answer += j;
gives:
1.2525e+11
real 0m0.677s
user 0m0.614s
sys 0m0.003s
So the difference cannot be due to loop overhead.
--
Bill Findlay
<surname><forename> chez blueyonder.co.uk
next prev parent reply other threads:[~2010-02-15 18:26 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-15 10:58 Is there an Ada compiler whose Ada.Numerics.Generic_Elementary_Functions.Log(Base=>10, X=>variable) is efficient? Colin Paul Gloster
2010-02-15 13:02 ` John B. Matthews
2010-02-15 14:17 ` Colin Paul Gloster
2010-02-15 17:19 ` John B. Matthews
2010-02-15 14:54 ` jonathan
2010-02-15 15:04 ` jonathan
2010-02-15 19:50 ` sjw
2010-02-16 16:50 ` Colin Paul Gloster
2010-02-15 18:26 ` (see below) [this message]
2010-02-15 18:51 ` jonathan
2010-02-15 20:00 ` sjw
2010-02-15 21:17 ` jonathan
2010-02-16 0:09 ` jonathan
2010-02-16 17:33 ` Colin Paul Gloster
2010-02-24 10:07 ` Colin Paul Gloster
2010-02-15 23:04 ` Jeffrey R. Carter
2010-02-16 14:54 ` Colin Paul Gloster
2010-02-16 15:24 ` Colin Paul Gloster
2010-02-16 19:01 ` Jeffrey R. Carter
2010-02-17 10:25 ` Colin Paul Gloster
2010-02-15 23:20 ` Randy Brukardt
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