Category:Z80 Assembly: Difference between revisions

===Bit Shifting===

The Z80 does have bit shifting, but thanks to RLCA and RRCA it's often faster to rotate instead. Compare the following two code snippets:

SLA A

SLA A

RLCA

RLCA

 

Not only is the second method shorter, it's also faster. The accumulator-specific bit rotates take 1 byte and 4 clock cycles each. They are different, however, because unlike the two-byte versions, these <i>do not affect the zero flag.</i> This isn't a big deal, however, as more often than not if you're rotating the accumulator you're not expecting to get zero as the output anyway.

 

If you want to know zero or not, you could also use this:

RLCA

RLCA

RLCA

 

For 16-bit bit shifting, use A instead of the other half of the register pair for faster results (unless you're checking for equality to zero, or you need the accumulator for something else.)

 

SRL H

RR L

SRL H

RRA

 

===Inlined bytecode===