[MP3 ENCODER] Small speedup for subs.c/fht()

[Mathew Hendry]

Hi all,

Another day, another little optimisation. I've added lookup tables to
subs.c/fht() to streamline the initial swapping operation for n==256 and
1024. This gives an overall speedup of 1-2% on my machine (PIII
500/NT4SP5/MSVC). The tables (particularly the n==1024 table) are quite
large, so it probably causes cache havoc, but the function is called often
enough for it to pay off... new version attached.

-- Mat.

subs_fht.c