Re: qcam on NetBSD
Thomas Davis writes:
> Russ Nelson writes:
> Where the code gets slow is the decoding of the 6bpp/uni-directional mode
> and the 4bpp/bi-directional mode. The nybble packing just kills things..
> (but makes for a fast transfer..)
Problem is that the stupid 386 doesn't have a barrel shifter (shifts
any number of bits in one cycle). Problem is the 6bpp mode has to
convert three 8-bit bytes into four 6-bit bytes, right? So burn some
memory. Build one 256-byte table and two 64Kbyte tables. Index into
them using the three bytes in turn. The 4bpp mode is even easier.
Hand-coded, optimized assembler will get you twice the speed of a C
-russ <firstname.lastname@example.org> http://www.crynwr.com/~nelson
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