The optimized filter gets enabled when the code is compiled
with -mcpu=/-march options set to target the processors which
support ARMv6 instructions. This code is also disabled when
NEON is used (which is a lot better alternative). For additional
safety ARM EABI is required and thumb mode should not be used.
Benchmarks from ARM11:
== 8 subbands ==
$ time ./sbcenc -b53 -s8 -j test.au > /dev/null
real 0m 35.65s
user 0m 34.17s
sys 0m 1.28s
$ time ./sbcenc.armv6 -b53 -s8 -j test.au > /dev/null
real 0m 17.29s
user 0m 15.47s
sys 0m 0.67s
== 4 subbands ==
$ time ./sbcenc -b53 -s4 -j test.au > /dev/null
real 0m 25.28s
user 0m 23.76s
sys 0m 1.32s
$ time ./sbcenc.armv6 -b53 -s4 -j test.au > /dev/null
real 0m 18.64s
user 0m 15.78s
sys 0m 2.22s
