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assemblyx86overflowinteger-overflow

Assembly, detecting overflow register

I have this very simple assembly code:

start:
add ax, 100    
; if ax overflow add to bx 1
jmp start

but i don't know how to detect ax register overflow, can anyone help me?

Solution

  • ADD instruction sets appropriate FLAGS reflecting the overflow condition. There are two kinds of overflow: signed and unsigned. You have to decide what's appropriate and use jc/jnc for unsigned and jo/jno for signed.

    add ax, 100
jnc noUnsignedOverflow
...
noUnsignedOverflow:

add ax, 100
jno noSignedOverflow
...
noSignedOverflow: