When interpolating with rate correction != 1.0, don't floor the
resulting input rate to the nearest smallest integer.
This allows rate corrections < 1/in_rate to have some effect, and
reduces jumps in the response. One of the jumps is inconveniently
between rate=1.0 and rate=1.0+eps and will cause rate corrections to
oscillate if target rate varies close to 1.0.
If phase is float, calculations in impl_native_in_len/out_len can
produce wrong results due to rounding error.
It's probably better to not be in the business of predicting
floating-point rounding, so replace this by fixed-point arithmetic.
Also make sure `offset+1` cannot overflow data->filter array in
do_resample_inter* due to float multiplication possibly rounding up.
We don't actually need to calculate the GCD for each resampler rate
update. The GCD is only used to scale the in/out rates when using the
full resampler and this we can cache and reuse when we did the setup.
The interpolating resampler can work perfectly fine with a GCD of 1 and
so we can just assume that.
Iterate the channels in the inner loop instead of the outer loop. This
makes it handle with 0 channels better but also does the more
complicated phase increment code only once for all channels. Also the
filters might stay in the cache for each channel now.
When we finished processing the history it might be possible that we
need to skip some samples from the input. Implement this by adding
a start offset for the samples in the buffer.
start with a completely filled resampler so that the first
input byte immediately gives an output sample. When then have
n_taps/2 leading (almost) 0 samples.
Also make the passthrough resampler act like the real resampler
by introducing an n_taps/2 delay.
Add a sinc based resampler that, unlike speex, avoids memcpy and
works directly on the source data. It also allows for ssse3
optimizations and aligned loads. It will later switch to table
interpolation when doing variable rate.
