[LAU] OT(ish): Strange coding problem (audio related)

[fons at kokkinizita.net]

On Sat, Jan 29, 2011 at 12:07:12PM +0100, Philipp Überbacher wrote:

> Took me a while to figure out that libm is part of glibc :)

It isn't. But it lives in /lib, not /usr/lib

> >   k = (int)(log2(x) + 1e-6)
> 
> log2() suffers from the same problem? I somewhat dislike the idea of
> adding a constant.

Everything floating point 'suffers from the same problem'.
Even addition. (1/3.0 + 1/3.0 + 1/3.0 == 1.0) doesn't have
to result in true. 

> >   int m, k;
> >   for (k = 0, m = 1; m < x; k++, m <<= 1);
> > 
> >   which will round up if x is not a power of 2.
> 
> Neat. I thought about it myself yesterday but my ideas weren't exactly
> brilliant. One idea was to divide by 2, the other to use a small 
> lookup table for powers of 2. I don't really know about efficiency, but
> I guess bit shifting is as efficient as it gets?

It's a single CPU cycle on most processors, and on some (e.g. ARM)
it can even be combined with other instructions.

Ciao,

-- 
FA

There are three of them, and Alleline.