Glenn Saunders wrote:
>I've developed this chart and I want to make sure it's correct.
>
>Please comment.
>
> ; CMP BRANCH WIZARD
> ;---------------------------------------
> ;A = M - use BEQ ; N=0,*Z=1, C=1
> ;A > M - use BCS ; N=0, Z=0,*C=1
> ;A < M - use BMI ; *N=1, Z=0, C=0
> ;A >= M - use BPL*; *N=0, C=1
> ;
> ; * No need to set carry ahead of time
>-
Your matrix should look like this:
opcode flags integer type
A == M BEQ N=0, Z=1, C=1
A != M BNE N=?, Z=0, C=?
A >= M BCS N=?, Z=?, C=1 (unsigned)
A > M BCS and BNE N=?, Z=?, C=1 (unsigned)
A < M BCC N=?, Z=0, C=0 (unsigned)
A >= M BPL N=0,;Z=?, C=? (signed)
A > M BPL and BNE N=0,;Z=0, C=? (signed)
A < M BMI N=1;;Z=0; C=? (signed)
The carry-flag is used for comparing unsigned integers, the negative flag for signed integers.
You can remember the flags easier, when you imagine CMP works like a subtraction (A-M):
- If the subtraction wraps around zero, then the carry-flag is cleared.
- If the result is negative, then the negative-flag is set.
-
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