Understanding Java bytes

Question

So at work yesterday, I had to write an application to count the pages in an AFP file. So I dusted off my MO:DCA spec PDF and found the structured field BPG (Begin Pag

Answer 1

For bytes with bit 7 set:

unsigned_value = signed_value + 256

Mathematically when you compute with bytes you compute modulo 256. The difference between signed and unsigned is that you choose different representatives for the equivalence classes, while the underlying representation as a bit pattern stays the same for each equivalence class. This also explains why addition, subtraction and multiplication have the same result as a bit pattern, regardless of whether you compute with signed or unsigned integers.