I not found Call NZ and Call Z on x86. ZX-Spectrum have.

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Roman

Joined: 21 Apr 2012
Posts: 1978

Roman 29 Dec 2018, 15:47

I was surprised when I did not find on x86
Call NZ and Call Z
Ret NZ and Ret Z

Useful commands.

On zx-spectrum was this commands.

29 Dec 2018, 15:47

Roman

Joined: 21 Apr 2012
Posts: 1978

Roman 29 Dec 2018, 15:50

emulation CAll nz

Code:

         cmp eax,10
         push lab1
         jnz ProcDoSomeCode
lab1:

Code:

ProcDoSomeCode:
    some code
    ret

29 Dec 2018, 15:50

Ali.Z

Joined: 08 Jan 2018
Posts: 822

Ali.Z 29 Dec 2018, 18:56

yeah really, it miss the conditional call.

but it can be implemented as:

Code:

there:
; somecode
pushf
pop ax
and al,40h
jnz here
call there ; callz
here:
; some code

Code:

there:
; somecode
pushf
pop ax
and al,40h
jz here
call there ; callnz
here:
; some code

_________________
Asm For Wise Humans

29 Dec 2018, 18:56

Furs

Joined: 04 Mar 2016
Posts: 2652

Furs 29 Dec 2018, 19:58

Roman wrote:

emulation CAll nz

Code:

         cmp eax,10
         push lab1
         jnz ProcDoSomeCode
lab1:

And very slow on modern CPUs with call return buffers / predictors. Wink

Also it always pushes, I don't think that's intentional and probably a bug (I don't know about ZX Spectrum).

Why not keep it simple like:

Code:

cmp eax, 10
jz @f
call ProcDoSomeCode
@@:

29 Dec 2018, 19:58

Roman

Joined: 21 Apr 2012
Posts: 1978

Roman 30 Dec 2018, 07:57

Furs
Yes good too

Code:

cmp eax, 10
jz @f
call ProcDoSomeCode
@@:

ZX-Spectrum was in 1982 !!!

I just show on example how useful Call Z or Call NZ.
One Call Nz or write 3 line code.

30 Dec 2018, 07:57

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20700
Location: In your JS exploiting you and your system

revolution 30 Dec 2018, 08:54

ARM in 32-bit mode can also do conditional calls.

But in 64-bit code that was eliminated.

C code compilers can't generated conditional call instructions, so the instructions are unused by most software. Therefore the CPU makers found no compelling reason to include it in the instruction set. And, as we all know, no one writes assembly code directly, by hand. OMG, that would be just too difficult for any human to do. Laughing

30 Dec 2018, 08:54

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