First of all, this adds a function that was missing in bsemathsignal: a
`fast_log2` implementation. It works by using the float exponent and
approximating the rest of the value using a polynomial. I found a tool that
gives optimal polynomial coefficients for a given order:
On 10.09.19 23:54, Tim Janik via beast wrote:
> Error samples, compared to LOG2L(3):
>
> +0.0, -0.0231613294631
Sorry, the first line was bogus, a "%+.1f" format string printed 0.01 as +0.0.
It should instead read:
Error samples, compared to LOG2L(3):
+0.1, +0.775829903
As mentioned on IRC, enabling optimizations with MODE=release and picking
clang++ (6.0 here) vs g++ (7.4 here) makes major differences when benchmarking
exp2f and log2f from glibc against our approximations. On a modern AMD64
processor, glibc is often faster. Internally it also uses polynomials
A bit of evaluation on Ubuntu 18.04:
- Bitwig defaults to opening JACK and issues a warning if that fails. It
provides JACK, ALSA and PulseAudio drivers. For the ALSA driver, the user has
to select one of the available ALSA hardware drivers (hw:*).
- Reaper defaults to opening JACK and issues
> Relative `exp2(x)` approximation errors in interval [-1:1]:
That's a miniscule range to approximate, given the valid range of this
function. Here are the errors of
bse_approx3_exp2() at mostly integer steps with some omissions for brevity:
-2.0, +0.0
-1.5,
