Cheat Engine

supercharger

i am confused about the use of:
test ah,01 / test ah,40 / test ah,41
after FNSTSW AX

do they produce the same result, or what is the difference?
i consulted www.intel.com but didn't find an explanation about those three.

Dark Byte · Posted: Sat Jul 10, 2010 11:08 am Post subject:

01 checks if "Invalid operation" was set in the status word of the fpu
40 checks if "stack fault" was set

41 checks for both at the same time

good doc:
Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 1: Basic Architecture
chapter 8

supercharger · Posted: Sat Jul 10, 2010 8:31 pm Post subject:

thanks, i found the use of TEST AH in float value comparison, in the Manual,chapter 8.

turbocharger · How do I cheat? Reputation: 0 Joined: 24 Apr 2011 Posts: 1

Since FNSTSW AX copies the floating point unit's status register into AX,
the TEST checks the high byte of the low word of the EAX register, which holds the condition codes of a previous floating point comparison:

ST(0) > m32fp => AH = 00h
ST(0) == m32fp => AH = 40h
ST(0) < m32fp => AH = 01h

So if you watch AH in your debugger, you can determine the result of a floating point comparison.