Multiplying/Dividing?
From: vic@physci.psu.edu (Vic Ricker)
To: "Super Famicom Development Group" <famidev@busop.cit.wayne.edu>
Subject: Re: Multiplying/Dividing?
Date: Sun, 26 Dec 93 16:29:09 EST
Take a look at this:
Address: $4202/$4203
Name: WRMPYA/WRMPYB
Description: Multiplier and multiplicand
D7 D6 D5 D4 D3 D2 D1 D0
| MULTIPLICAND-A | $4202
|_______________________________________|
D7 D6 D5 D4 D3 D2 D1 D0
| MULTIPLIER-B | $4203
|_______________________________________|
These registers perform absolute multiplication by multiplying multiplicand A by multiplier B and return product C which can be read from $4216/$4217 RDMPY.
Set register A, then B. After the B register is set, it will take 8 machine cycles for the multiplication to be completed.
* The A register will not be destroyed by the multiplication process.
^^^ does not refer to the accumulator. it means the multiplicand
Also, there is 8/16 multiply that shares the mode 7 matrix registers: set 16 bit multiplier to $211b and 8 bit multiplicand to $211c the 24 bit product will be placed in $2134-$2136.
The shift-add routine is a great way to multiply. I'm suprised that so many so-called assembly programmers don't know how to do it.
Regardless of how fast it is, the hardware stuff blows it away.
There is also a hardware divide:
$4204/4205 is the 16 bit dividend, $4206 is the 8bit divisor, the quotient will be put in $4214, and the remainder in $4216/4217.
ANy questions, lemme know.
