Cheat Engine

supercharger · Posted: Wed May 05, 2010 3:58 am Post subject: what is the negative of 80 ?

since
neg 0 = 0
neg 1 = ff
neg 7f = 81
then neg 80 = 80 ?
is it a positive value or negative value?

if 80 is negative value, then neg 80 should be a positive value, right?
but 80 = 80 , right?

Pingo · Posted: Wed May 05, 2010 5:08 am Post subject:

Dont write it as byte value, use 2byte or 4byte
2byte
neg 0x80 = 0xFF80
pos 0x80 = 0x0080

4byte
neg 0x80 = 0xFFFFFF80
pos 0x80 = 0x00000080

Slugsnack · Posted: Wed May 05, 2010 7:42 am Post subject:

look up two's complement on the internet

Jani · Posted: Wed May 05, 2010 7:46 am Post subject:

Why don't you test it out yourself..

Slugsnack · Posted: Wed May 05, 2010 7:51 am Post subject:

Another easy way is to open up OllyDbg and double-click register values and play around with those since they have the representation in hex/binary/signed/unsigned.

kot1990 · Posted: Wed May 05, 2010 4:43 pm Post subject:

if you talk about 1 byte then only the unsigned byte has a positive value 0x80 <-- which is +128 in decimal, unsigned byte is 0x00 - 0xFF equivalent 0-255 in decimal, but there are no negative values.

Now if you talk about signed byte, the number +128 in decimal does not fit in 1 byte because the signed byte is as follows

positives 0x00 - 0x7F ->> decimal 0 - +127 <-- +127 is the max positive that you can represent with 1 byte.

negatives 0x80 - 0xFF ->> decimal -128 - -1 (-128 is 0x80 and -1 is 0xFF)

So as you understand you'll need a second byte Smile

which can handle 65535 different values.

So with 2 bytes -1 is 0xFFFF . So if 0x80 is +128 (unsigned) and 0xFFFF is -1 then you should go backwards and do 0xFFFF - 0x80 +1 (+1 because -1 -128 = -129) wich is 0xFF80 Smile

. I hope you'' figure it out time-time/.

EDIT: if you use the calculator and select WORD wich is 2 bytes, and type FF80 it will show the positive value because WORD is unsigned.