Compare

Our comparison instruction has this mnemonic:

CMP reg0, *(reg1), *(reg2)

Registers reg1 and reg2 both contain a pointer to memory. The result of the comparison is saved in register reg0.

Comparison can be be implemented as a substraction. Let’s say the memory cell that reg1 points to has value val1 and the memory cell reg2 points to value val2. Then we have:

condition	reg0
val1 > val2	>0
val1 = val2	0
val1 < val2	<0

    …
elif (n3 == 0xF): # CMP reg0, *(reg1), *(reg2)
    self.R[n2] = self.mem.peek(self.R[n1]) - self.mem.peek(self.R[n0])
    …

Note: This implementation does not take care to wrap this back into the proper bit width.