assemblyx86eflags

Assembly: do MOV or DEC influence zero flag?


In a disassembled code:

movsx eax,[address1]
# a few fpu computations
dec eax
# so many fpu computations
jz label2

If fpu computations do not influence zero flag, then we can assume that it is equal to:

# a few fpu computations
# so many fpu computations
movsx eax,[address1]
dec eax
jz label2

Then, my question is that do mov or dec have any influence on zero flag?


Solution

  • Of course you should look this up in the manuals but here's a general rule:

    So movsx falls in the first category and will not change any flag.
    But dec clearly does a computation and most certainly changes several flags including the ZeroFlag.