I wanted to see if my understanding is correct on this... I figured out multiplication, but I'm not quite sure how division would work. Please correct any mistakes.
Code: Rla Multiplication
a * b
1. RRA B
2. Push the flags (af)
3. RLA A, DEC B
4. Repeat 3 until B=0
5. Pop the flags (af)
6. If c, then add the original a to a. If nc, you are done.
Code: Rra Division
a / b
1. RRA B
2. Push the flags (af)
3. RRA A, DEC B
4. Repeat 3 until B=0
5. Pop the flags (af)
6. If nc, you are done. If c, [what would I do here?]
[/code]
What do you have against using the wonderful routines from z80Bits? I strongly, strongly recommend that you read these thoroughly, understand how they work, and then use them.
http://baze.au.com/misc/z80bits.html
Well, I don't have anything against them. I'm just interested in demonstrating mult/div via bit rotation in my tutorial.
ACagliano wrote:
Well, I don't have anything against them. I'm just interested in demonstrating mult/div via bit rotation in my tutorial.
Bit rotation is good for division, mostly for powers of two though. For multiplication adding something to itself is a faster way to multiply by two than shifting generally (only a very small speedup, but if you need a fast routine, sla a is slower than add a, a...)
I suggest you actually go through the ones Kerm told you to look at; pick those apart, and you'll see some neater and more optimized routines, and you can learn a lot more 
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