jecxnz or similar

[Gian Piero]

Hi Geremy,I sent a previous email, but it was sent during the winter holiday, sorry about it.
I am using the instruction jecxz a lot with the GoAsm.
Now, I know that every conditional jump instruction has always the opposite condition instruction, however I got an error during the compilation of the instruction jecxnz.
Is maybe such instruction misspelled ?
Alternatively I could use maybe jecxGT or jecxLT or jecxGE or jecxLE etc
Thanks
Gian

[MazeGen]

Wrong forum.

There is nothing like JECXNZ instruction, or JECXGE, or JECXLE (the latter ones don't make any sence, by the way). You have to use this construct instead of JECXNZ:

Code Select Expand


cmp ecx, 0
jne lbl


[Gian Piero]

Thanks for the precious information.
Goasm reflects the microarchitecture of most recent procs, it seems like AMD and INTEL built this instruction without its "opposite condition" counterpart.
By the way, the popcnt instruction has been now implemented by AMD and INTEL, however Goasm has not implemented it.
Cheers

[MazeGen]

Goasm reflects the microarchitecture of most recent procs, it seems like AMD and INTEL built this instruction without its "opposite condition" counterpart.

Yes, because JECXZ was designed as a helper instruction for LOOP loops. Something like this:

Code Select Expand


mov ecx, COUNT

top:
; here goes code which further modifies ECX

jecxz break   ; prevent overflow of ECX counter , which would happen on LOOP instruction in case ECX is zero

; some other instructions

loop top

break: