Re: [avr-gcc-list] how to infer lsl instruction...

[Royce Pereira]

Hi
On Wed, 16 Nov 2005 13:00:03 +0530, varsha <address@hidden>  
wrote:

> Hello all,
> i'm using avr-gcc (GCC) 3.4.3 compiler and Atmega 16 as a MCU.
>
> for crc calculation i'm using inline assembly code.
> for example..
>
> __asm__ __volatile__
>    (
>     "lsl r11"    "\n\t"
>     "rol r12"    "\n\t"
>     "rol r13"    "\n\t"
>     "rol r15"
>    );
>
> but compiler doesn't generate lsl instruction...
> it generates something like this..
>
>     1514: bb 0c        add r11, r11
>     1516: cc 1c        adc r12, r12
>     1518: dd 1c        adc r13, r13
>     151a: ff 1c        adc r15, r15
>
>
> so what should do to if i want compiler to generate lsl instruction.

If the bytes & execution time is the same, why should make any difference,  
as long as it acheives the same result. Left shift is the same as  
multiplying by 2, which is the same as adding a value to itself. Hence the  
resulting code.

--Royce.




> thank you,
>
>
> regards,
> varsha
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