sbc: slightly faster 'sbc_calc_scalefactors_neon'
Previous variant was basically derived from C and MMX implementations.
Now new variant makes use of 'vmax' instruction, which is available in
NEON and can do this job faster. The same method for calculating scale
factors is also used in 'sbc_calc_scalefactors_j_neon'.
Benchmarked without joint stereo on ARM Cortex-A8:
== Before: ==
$ time ./sbcenc -b53 -s8 test.au > /dev/null
real 0m3.851s
user 0m3.375s
sys 0m0.469s
samples % image name symbol name
26260 34.2672 sbcenc sbc_pack_frame
20013 26.1154 sbcenc sbc_analyze_4b_8s_neon
13796 18.0027 sbcenc sbc_calculate_bits
8388 10.9457 no-vmlinux /no-vmlinux
3229 4.2136 sbcenc sbc_enc_process_input_8s_be_neon
2408 3.1422 sbcenc sbc_calc_scalefactors_neon
2093 2.7312 sbcenc sbc_encode
== After: ==
$ time ./sbcenc -b53 -s8 test.au > /dev/null
real 0m3.796s
user 0m3.344s
sys 0m0.438s
samples % image name symbol name
26582 34.8726 sbcenc sbc_pack_frame
20032 26.2797 sbcenc sbc_analyze_4b_8s_neon
13808 18.1146 sbcenc sbc_calculate_bits
8374 10.9858 no-vmlinux /no-vmlinux
3187 4.1810 sbcenc sbc_enc_process_input_8s_be_neon
2027 2.6592 sbcenc sbc_encode
1766 2.3168 sbcenc sbc_calc_scalefactors_neon
1 file changed
