How does a negated compare work?

[Ian_Brooks]

Homework Statement

I understand that in the ARM architecture
CMP a1, a2

will take the difference between a1 and a2 and make a decision based on its flags
NZCV - if the difference is positive a1 > a2, and vice versa

But how does a negated cmp work?

CMN a1, a2 ?

Is it the opposite?

Homework Equations

The Attempt at a Solution

see above. the internet gives me nothing

 

[GTrax]

CMP means Compare values
CMN means Compare Negated values

The ARM instruction sets are widely published, but here is a link to a help page

http://www.heyrick.co.uk/assembler/cmp.html#cmn
I am sure you will be able to figure it out from there.

 

[Ian_Brooks]

thanks for the link -

If
cmp a1, a2 ; performs a subtraction
cmn a1, a2 ; performs a subtration with the second opperand being negative or
...;a1-(-a2) so its the same as an add, so what's the benefit of using cmn besides branching?