DOS ain't dead

Assembler optimisation - how to avoid a jump? (Developers)

posted by ecm  , Düsseldorf, Germany, 13.05.2012, 23:32

> I would like to write nice code. I know I could somehow remove the ugly
> jump "jnc @RLE_CLIP_MOVE_CONT" but I don't know how.

Hmm, I'm not very good at this. (Usually, I try to rather optimise for code size, and in pure 8086-compatible code.) But let me try.

> sub edx,ecx
> jnc @RLE_CLIP_MOVE_CONT
>
> add ecx,edx
>
> @RLE_CLIP_MOVE_CONT:

The following assumes that eax is available:

        sub edx, ecx
        rcr eax, 1
        sar eax, 31
        and eax, edx
        add ecx, eax

This does avoid the jump, but I don't know whether it is actually much better speed-wise.

---
l

Complete thread:

• Assembler optimalisation - how to avoid a jump? - Laaca, 13.05.2012, 20:38 (Developers)
  • Assembler optimalisation - how to avoid a jump? - Rugxulo, 13.05.2012, 21:10
    • Assembler optimalisation - how to avoid a jump? - Laaca, 13.05.2012, 22:15
      • Assembler optimalisation - how to avoid a jump? - marcov, 13.05.2012, 23:22
  • Assembler optimisation - how to avoid a jump? - ecm, 13.05.2012, 23:32
    • Assembler optimisation - how to avoid a jump? - Laaca, 14.05.2012, 18:15
      • Assembler optimisation - variant 3, sbb - ecm, 14.05.2012, 18:22
      • Assembler optimisation - how to avoid a jump? - Rugxulo, 16.05.2012, 10:34
        • Assembler optimisation - how to avoid a jump? - bretjohn, 16.05.2012, 16:42
          • Assembler optimisation - speed, size, etc - ecm, 16.05.2012, 16:59