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Re: [avr-gcc-list] swap bits

From: Volkmar Dierkes
Subject: Re: [avr-gcc-list] swap bits
Date: Tue, 21 Jan 2003 17:49:09 +0100


Torsten Hahn <address@hidden> schrieb am 21.01.03 17:31:34:
> iam looking for a way, to efficiently swap all bits in an register. Can 
> somebody help me with a little asm-macro or a pice of efficient c-code ?
> It schould take an 8bit value as input an give back an value, where bi7 
> of the input is now the bit 0, bit6 is bit1 etc.

What do you mean with efficiently? bytes or time?

Quick is a lookup table, but it needs 256 bytes for the table plus some less 
bytes for the access to the table.

one other may be (not tested):
value in r16, output in r17.
LDI r18,8
ROL r16
ROR r17
SUBI r18,1
BRNE loop

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