[Flac-dev] Altivec Optimizations

[Chris Csanady]

Hi,

I have been playing with Altivec, and I rewrote a couple of the routines
in assembly.  Looking at the archives, I noticed that there may already
be some effort on this.  Anyways...

Right now, I have two routines working.  They need to be cleaned up, 
made
relocatable, and documented; otherwise, they seem to work fairly well.  
I
see an overall ~27% speed improvement when encoding with the default
settings, and greater at -8.

The ones I have done are:

	FLAC__lpc_compute_residual_from_qlp_coefficients_16_bit()
	FLAC__lpc_compute_autocorrelation()

I did make a change in stream_encoder.c to better align the data passed 
to
FLAC__lpc_compute_residual_from_qlp_coefficients(), I hope this is ok.  
Most
occurrences of residual are replaced with residual+order as in:

	FLAC__fixed_compute_residual(signal+order, residual_samples, order, 
							 residual+order);
	...
	subframe->data.fixed.residual = residual+order;

The vectors in Altivec must be 16 byte aligned, and it complicates 
things
if signal[] and residual[] are not aligned.

Chris