chris@mimsy.UUCP (Chris Torek) (11/12/88)
In article <866@cernvax.UUCP> hjm@cernvax.UUCP (Hubert Matthews) writes: >The INMOS T800 has an instruction bitrevword, which turns a >little-endian word into a big-endian word, effectively doing a >reflection in the middle. ... In software, it takes quite some time. >In hardware it takes just over 1 microsecond on a 30MHz part. The MIT X Window system library has to reverse the bits in a byte, word, or longword. It uses a 256-element table lookup, possibly iterated (unrolled) for word and longword flips. Expand the table to 16 bits (65536 elements) and you can do it in 4 VAX instructions; otherwise it takes 8. Not so slow after all. . . . (Of course, PCC does not manage to use 8 instructions, at least not without much help.) -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@mimsy.umd.edu Path: uunet!mimsy!chris