[fpc-pascal] Reversing bit-order of byte

[Koenraad Lelong]

On 03-05-12 13:27, Thomas Schatzl wrote:
...
> function reverse(b : byte) : byte; assembler; nostackframe;
> asm
>    rbit r0, r0
>    // rbit reverses the whole word, so now you have
>    // your value in bits 31-24... so shift right by that amount
>    // should fix this up (bits 23-0 contain junk, we shift that out
>    // anyway)
>    lsr r0, r0, #24
> end;
>
> However, this may not compile because fpc may not recognize the rbit
> instruction.
>
> Following is a version that encodes the instruction directly, retrieved
> from disassembling some gcc code:
>
> function reverse(b : byte) : byte; assembler; nostackframe;
> asm
>    .long 0xe6ff0f30 // rbit r0, r0
>    lsr r0, r0, #24
> end;
>

Thanks guys, I'll try and test this weekend.

Regards,

Koenraad Lelong.