Difference between je and jz.

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Roman

Joined: 21 Apr 2012
Posts: 1766

Roman 15 Jul 2022, 02:04

Why exist je and jz?
I always using jz or Jnz.

15 Jul 2022, 02:04

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 15 Jul 2022, 02:12

Same encoding. No difference whatsoever.

15 Jul 2022, 02:12

I

Joined: 19 May 2022
Posts: 58

I 15 Jul 2022, 02:37

One has an 'e' the other a 'z' :p

Comparing 2 registers if they are equal by subtraction results in zero flag being set if so.

With AND operator 2 AND 2 while equal is not zero, it's 2. So je will fail because it's really zero flag check. e can sound illogical sometimes, IMO!

Edit: Replaced 'numbers' with 'registers' because if for example eax represents a signed number such as -2 and ebx an unsigned number 4,294,967,294 cmp eax,ebx will set the zero flag and je will jump

Last edited by I on 15 Jul 2022, 05:26; edited 1 time in total

15 Jul 2022, 02:37

bitRAKE

Joined: 21 Jul 2003
Posts: 4020
Location: vpcmpistri

bitRAKE 15 Jul 2022, 03:17

I tend to use Z because the flag is the Z-flag; and the letter E is already too common. It's just personal preference though.

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15 Jul 2022, 03:17

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 15 Jul 2022, 04:10

Code:

cmp eax,ebx
je foo ; are eax & ebx equal?

dec ecx
jz foo ; is ecx zero?

15 Jul 2022, 04:10

Roman

Joined: 21 Apr 2012
Posts: 1766

Roman 15 Jul 2022, 04:38

I reading je op code = jz
And je the same as jz

15 Jul 2022, 04:38

macomics

Joined: 26 Jan 2021
Posts: 926
Location: Russia

macomics 15 Jul 2022, 04:47

I would have asked something more interesting. For example: the difference between jp (parity, efl.pf = 1) and jpe (parity even, efl.pf = 1) or jnp (not parity, efl.pf = 0) and jpo (parity odd, efl.pf = 0) or jnb (not below, efl.cf = 0) and jnc (not carry, efl.cf = 0) and jae (above and equal, efl.cf = 0). It is exactly the same as between je (equal, efl.zf = 1) and jz (zero, efl.zf = 1).

ADD: Better study the difference between jae (above and equal, efl.cf = 0) and jge (greater and equal, efl.sf xor efl.of = 0)

15 Jul 2022, 04:47

AsmGuru62

Joined: 28 Jan 2004
Posts: 1619
Location: Toronto, Canada

AsmGuru62 16 Jul 2022, 23:34

revolution is right: JE/JZ used for readability of the source, but it is a same instruction.

16 Jul 2022, 23:34

I

Joined: 19 May 2022
Posts: 58

I 18 Jul 2022, 01:22

Same

Code:

ja      jnbe
jb      jnae
jna     jbe
jnb     jae

jz      je
jnz     jne

jg      jnle
jl      jnge
jng     jle
jnl     jge

18 Jul 2022, 01:22

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