I am learning High Level Assembly Language at the moment, and was going over the concept of signed and unsigned integers. It seems simple enough, however getting to sign extension has confused me.
Take the byte 10011010 which I would take to be 154 in decimal. Indeed, using a binary calculator with anything more than word selected shows this as 154 in decimal.
However, if I select the unit to be a byte, and type in 10011010 then suddenly it is treated as -102 in decimal. Whenever I increase it starting from a byte then it is sign extended and will always be -102 in decimal.
If I use anything higher than a byte then it remains 154 in decimal.
Could somebody please explain this seeming disparity?
When you select the unit as a byte the MSB of
10011010is treated as the signed bit, which makes this one byte signed integer equivalent interpretation to -102 (2’s complement).For integers sized large than 8 bits, say 16 bits the number will be:
0000000010011010which do not have 1 in MSB therefore it is treated as a positive integer whose integer representation is 154 in decimal. When you convert the 8 bit byte to a higher type the sign extension will preserve the -ve interpretation in the larger length storage too.