Hello! I'm trying to understand the FASM TrayIcon example, but got stuck at the beginning-code:

Line 1 to 3 are clear to me, but then the magic begins. eax is XORed with itself, and later eax is shifted into wc.style....? This has to mean that eax holds the same value every time after GetModuleHandle was invoked? Otherwise i can't explain that the programmer shifted eax into wc.style - if he doesn't know what it holds. But how can i explore what the registers hold at specific points? And why does GetModuleHandle always returns the same Instance-Handle? Thank you.

hey, after the call to GetModuleHandle eax holds the handle since eax is used for return values, if you send 0 to GetModuleHandle it returns the current module, or you can specify the name for a specific handle (see the MSDN)

about xor:

"Each bit of the result is 1 if the corresponding bits of the operands are different; each bit is 0 if the corresponding bits are the same."

since its xor eax, eax, each bit would be the same (obviously) so all 32bits get set to 0, its a trick to make eax 0 without using an immediate or memory and its generally faster

so


is the same as


i hope that clears it up

when you xor something with itself then it becomes zero. so it is just moving zero to wc.style. about xoring: 1 xor 1 = 0, 0 xor 0 = 0, so when you xor something with itself it always becomes 0.

i guess you were writing yours just as i posted my reply :p

Ah, that's clear now! Thx for the help!

redghost: yup...