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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 13:17:25 -0800 (PST)
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Date: 2010-02-15T13:17:25-08:00
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On Feb 15, 8:00=A0pm, sjw <simon.j.wri...@mac.com> wrote:
> On Feb 15, 6:26=A0pm, "(see below)" <yaldni...@blueyonder.co.uk> wrote:

> > 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.

Right ... there was never any mystery here ... that's why I thought a
translation of the original bench wasn't necessary. The remaining
puzzle
is the smallish difference between the gnat Log and the gcc Log. I
will
(also) leave this to the experts.  When I looked at this in the past,
it has always been because gnat did the calculation to 18
significant
figures (even if you use type Real is digits 15), gcc to 15.

Jonathan