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From: sjw <simon.j.wright@mac.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 12:00:52 -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++.

I think it's a mixture of your point & Jonathan's; the loop body, with
the 500 calls to log10(), is executed once, then the compiler smartly
realizes that each iteration produces the same increment.