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Excerpts from fons's message of 2011-01-29 13:46:19 +0100:

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> On Sat, Jan 29, 2011 at 01:22:10PM +0100, Philipp Überbacher wrote:

>

> > I thought that log2() might use a different routine if the argument is a

> > power of 2. I guess that even if it does it's nothing to rely on because

> > another libm implementation might not do the same thing.

>

> There are very good reasons why math routines don't do such things.

What are those?
> > Why did you choose 1e-6 specifically?

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>

> It does the job. 1e-6f will also work for single precision.

>

> > ...  Without optimisation the output is quite

> > different, but beginning with -O2 the machine code appears all the same.

>

> That could well be completely different on an another CPU and compiler,

> and even more so if tested ***in context***. Such tests are really

> pointless, in particular if you consider the actual use of this code.

> It isn't executed 100 times for each audio sample.

Thanks, I see this now after Peter did another test with quite different

results. I looked at it out of context because I simply don't understand

the context. I only know what a ft does but not how it works, nor have I

implemented a fft, so the code with its two-letter variables is

meaningless to me.
> > If the optimised code really is the same is it worth it to use funky bit

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> > shifting operations?

>

> There's nothing funky about them, they are part of C and C++.

They were funky to me mainly because I had to look them up but also

because operating on the bit representation requires a different mode of

thinking. I bet it also has its own set of pitfalls.

It's quite interesting that it still seems to make a difference

performance-wise. Thanks  for your insights.
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