sbc: faster 'sbc_calculate_bits' function
By using SBC_ALWAYS_INLINE trick, the implementation of 'sbc_calculate_bits'
function is split into two branches, each having 'subband' variable value
known at compile time. It helps the compiler to generate more optimal code
by saving at least one extra register, and also provides more obvious
opportunities for loops unrolling.
Benchmarked on ARM Cortex-A8:
== Before: ==
$ time ./sbcenc -b53 -s8 -j test.au > /dev/null
real 0m3.989s
user 0m3.602s
sys 0m0.391s
samples % image name symbol name
26057 32.6128 sbcenc sbc_pack_frame
20003 25.0357 sbcenc sbc_analyze_4b_8s_neon
14220 17.7977 sbcenc sbc_calculate_bits
8498 10.6361 no-vmlinux /no-vmlinux
5300 6.6335 sbcenc sbc_calc_scalefactors_j_neon
3235 4.0489 sbcenc sbc_enc_process_input_8s_be_neon
2172 2.7185 sbcenc sbc_encode
== After: ==
$ time ./sbcenc -b53 -s8 -j test.au > /dev/null
real 0m3.652s
user 0m3.195s
sys 0m0.445s
samples % image name symbol name
26207 36.0095 sbcenc sbc_pack_frame
19820 27.2335 sbcenc sbc_analyze_4b_8s_neon
8629 11.8566 no-vmlinux /no-vmlinux
6988 9.6018 sbcenc sbc_calculate_bits
5094 6.9994 sbcenc sbc_calc_scalefactors_j_neon
3351 4.6044 sbcenc sbc_enc_process_input_8s_be_neon
2182 2.9982 sbcenc sbc_encode
1 file changed
