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Re: [avr-gcc-list] How to get the GCC to use the swap instruction?
From: |
Christian Ludlam |
Subject: |
Re: [avr-gcc-list] How to get the GCC to use the swap instruction? |
Date: |
Wed, 30 Oct 2002 10:38:24 +0000 |
User-agent: |
POPstar/2.02 |
On 30 Oct Marek Michalkiewicz wrote:
> When rotlqi3 is implemented, simple ((a << 4) | (a >> 4)) would be
> equivalent. Rotation in general (even by unknown number of bits) could be
> optimized as well, by making use of the carry flag - like this (for rotate
> left by 1, repeat in a loop as needed):
>
> lsl %0
> adc %0,__zero_reg__ ; set bit 0 to C flag
Or even
adc %0,%0
This is how AVR assemblers assemble the ROL instruction (and LSL by
add %0,%0); the AVR core provides ROR and LSR itself.
--
Christian Ludlam
address@hidden
avr-gcc-list at http://avr1.org
[avr-gcc-list] movin' up to Linux, Marlin Unruh, 2002/11/03
Re: [avr-gcc-list] How to get the GCC to use the swap instruction?, Bruce D. Lightner, 2002/11/03