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In my book it says that LOOPZ works like this...
ECX = ECX - 1
if ECX > 0 and ZF = 1 then jump <label>
Eh? How is it possible for that condition to be true?? if ECX is greater than 0 then surely its not possible for ZF to be 1, thats like saying...
if ECX > 0 and ECX = 0 then jump <label>
What am I missing here?
Do these links help any?
http://enrico.phys.cmu.edu/QCDcluste...ence/vc162.htm
http://faydoc.tripod.com/cpu/loopz.htm
http://docs.sun.com/app/docs/doc/802...oo?l=fr&a=view
Looks like th ZF flag is not affected by the change in ECX, but from other things within the loop.
Hope that helps.
AFAIK, it means that while ECX > 0 and ZF = 1 then execute the THEN statement, if either one of them fails, i.e. IF ECX > 0 but ZF = 0 (or not equals 1) then execute the ELSE statement or come out of the IF statement.Quote:
Originally Posted by wossname
but i may be wrong, it's been a long time since i touched Assembly language.
I think Andy is closer. If I can remember that entire book on x86 assembly, it said that the CX register didn't directly change the ZF flag value.
chem
read this, else look at the links provided by Andy for details:
Quote:
Some forms of the loop instruction (LOOPcc) also accept the ZF flag as a condition for terminating the loop before the count reaches zero. With these forms of the instruction, a condition code (cc) is associated with each instruction to indicate the condition being tested for. Here, the LOOPcc instruction itself does not affect the state of the ZF flag; the ZF flag is changed by other instructions in the loop.
Wow this is an old thread. I worked this out days ago :D
It occured to me that the loop instructions don't affect ZF.
BTW...since you are interested in performance...avoid LOOPcc ...it is slower on newer PCs (newer than 486 :) )