Excerpts from fons's message of 2011-01-28 16:11:52 +0100: > On Fri, Jan 28, 2011 at 02:02:36PM +0100, Philipp Ãberbacher wrote: > > > rant_begin > > Why can't log mean the same thing everywhere? Why does it need to be > > base e here and base 10 there? Why is there no consistency? > > And why is there no proper logarithmus dualis function? Because you > > can simply do log(n)/log(2)? We've just seen how well this works. > > How about: > > log() - base 10 > > ln() - base e - logarithmus naturalis > > ld() - base 2 - logarithmus dualis > > rant_end > > Libm has log(), log10, and log2(). Took me a while to figure out that libm is part of glibc :) Good to know that those functions are available on probably pretty much all linux systems. > > The next obvious question is: Does the inaccuracy reliably result in > > values bigger than 11? > > No. > > If the input is a power of two, and you expect an integer as > a result, just do > > k = (int)(log2(x) + 1e-6) log2() suffers from the same problem? I somewhat dislike the idea of adding a constant. > or > > k = (int)(log(x)/log(2) + 1e-6) > > or > > 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? Anyway, it's a neat way to avoid the problem and the rounding properties of mult/div in case of not power of 2 could be useful as well. Regards, Philipp _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
