Just wondering...

[The_Grey_Beast]

Can rep be used for other instructions than string operations? For example:

Code Select Expand

; add ax to itself 6 times
mov ecx, 6
rep add ax, ax

Does the above code work? Thanks.

[roticv]

No.

[Tedd]

REP is only for MOVS/LODS/CMPS/SCAS/INS/OUTS
For all other instructions it's 'illegal' (technically, it's 'undefined' - ie. you shouldn't use it.)

The LOOP instruction does what you want though (just don't mention this to any of the optimizer freaks :lol)

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   mov ecx,6
@loopy:
   add ax,ax
   loop @loopy


(obviously, a number of instructions can go in the 'loop' - as long as the jump is still short)

[hutch--]

Code Select Expand


    mov ecx, -6
  @@:
    add ax, ax
    add ecx, 1
    jnz @B