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.