Further speedup in cwrsi() by using the special case for n=2
Split cwrsi() by pulses vs. dimensions.

This lets us cut out a bunch of work in the large _n, small _k case
 where most of the dimensions won't have any pulses.
It also gets rid of all remaining usage of CELT_PVQ_U() in cwrsi(),
 leaving just a single test instead of lots of mins and maxes, and
 makes a bunch of the jump threading more obvious.

This is a 1.6% decoder speedup on a 96 kbps comp48-stereo encode on
 a Cortex A8.
Don't call denormalise_bands() on silence
Moves log2Amp inside denormalise_bands() and get rid of bandE[]

Also get rid of the MSE measurement code which is outdated and no longer useful
Converts denormalise_bands() to use 16-bit multiplications
Avoids symbol clashes with Speex (pitch_xcorr) and libm (y1)
SSE optimization of comb_filter()

Should make it easy to adapt to other architectures.
Use __declspec(dllexport) on mingw build.

Signed-off-by: Gregory Maxwell <greg@xiph.org>
Only enable non-multiple of 4 in comb_filter_const() when CUSTOM_MODES is on
Enable SSE for MSVC

Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>
Makes dual_inner_prod() more generic to increase its use