Quote:
Originally Posted by Photon
SUB and CMP should use the exact same logic, cmp is sub without store. From memory there is no time gain (or loss of time loss  ) for An as there is for Dn (on 68000) because of the extra operations (also includes ADD). I.e. if you go by 6c instead of 8c check footnotes.
Code:
move.l #$0ffffffff,a0
sub.w a0,a0
move.l #$ffff0fff,a1
sub.w a1,a1
a0=$10000000
a1=$ffff0000
SUB and SUBA -> SUBA instruction, according to AsmOne debugger. Is there a way to get a separate, different SUB <ea>,An opcode? |
a0 = $00000000
the sub.w a0,a0 uses a0.w sign extended
$ffff -> $ffffffff
$ffffffff - $ffffffff = $00000000
the word used in adda/suba is sign extended before a long add/sub is calculated