How to reverse bits...
J.T. Conklin
jtc at motcad.portal.com
Wed Aug 15 06:32:12 AEST 1990
In article <2059 at ux.acs.umn.edu> dhoyt at vw.acs.umn.edu writes:
>In article <1990Aug13.185757.3236 at sti.fi>, ttl at sti.fi (Timo Lehtinen) writes...
>>This might be trivial, but here goes...
>>What's the most optimal way to reverse the bits in an unsigned char,
>>i.e. change from MSB to LSB ordering ?
>
> You don't have to change anything. Big and little endians only cause
>trouble when you look at different integer formats. Bytes is bytes, as they
>say.
The question was how to flip the bits in an unsigned char, not a bytes
in a word. Like has been indicated in previous postings, a 256 element
lookup table is the best way to perform this task.
For example, most fax machines/modems present the bits in lsb-to-msb bit
order. If your G3 decompression code was written for msb-to-lsb order,
bit reversal is needed.
Another useful table is one that flips the bits 1-for-0,0-for-1. This
is useful for inverting an image.
--jtc
--
J.T. Conklin UniFax Communications, Inc.
CADnet Inc, San Ramon California
jtc at motcad.portal.com, ...!portal!motcad!jtc
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