Two's complement
You are encouraged to solve this task according to the task description, using any language you may know.
wp:Two's_complement Two's complement is an important concept in representing negative numbers. To turn a positive integer negative, flip the bits and add one.
- Task
Show how to calculate the two's complement of an integer. If the technique is different depending on the size of the integer, give an example of each.
Z80 Assembly
8-Bit
Zilog Z80
<lang z80>ld a,%00001111 neg ;returns %11110001 in a</lang>
Game Boy <lang z80>ld a,%00001111 cpl ;game boy doesn't have NEG but it has CPL which flips all the bits. inc a ;returns %11110001 in a</lang>
16 Bit
NEG and CPL only work on the accumulator A.
The following can be written to work with BC, DE, HL, IX, or IY.
<lang z80>xor a ;ld a,0
sub c
ld c,a
sbc a ;loads &FF into A if "sub c" set the carry (borrow) flag. Otherwise, a remains zero.
sub b
ld b,a</lang>