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