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From: jonathan <johnscpg@googlemail.com>
Newsgroups: comp.lang.ada
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 10:51:41 -0800 (PST)
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On Feb 15, 6:26=A0pm, "(see below)" <yaldni...@blueyonder.co.uk> wrote:
> On 15/02/2010 10:58, in article
> alpine.LNX.2.00.1002151055530.17...@Bluewhite64.example.net, "Colin Paul
>
> Gloster" <Colin_Paul_Glos...@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 =A0 =A00m33.918s
> user =A0 =A00m33.864s
> sys =A0 =A0 0m0.025s
>
>... if I replace the C++ loop body by:
>
> =A0 =A0 =A0 for(int j=3D1; j<=3D500; ++j)
> =A0 =A0 =A0 =A0 =A0answer +=3D std::log10(j*0.100000000000000000000);
> It now gives:
>
> 6.34086e+08
> real =A0 =A00m18.112s
> user =A0 =A00m18.082s
> sys =A0 =A00m0.015s
>

> Bill Findlay
> <surname><forename> chez blueyonder.co.uk

On my computer,
   Log_base_10_of_e * Log (y)
is twice as fast as
   Log (y, Base =3D> 10.0).


Jonathan