3. Multiplication

3.4. Optimized Multiplier

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Iteration	Step	Multiplicand	Product
0	Initial values	0010	0000 0011
1	1 : 1 ⇒ Product += Multiplicand		0010 0011
	2 : Shift Product right		0001 0001
2	1 : 1 ⇒ Product += Multiplicand		0011 0001
	2 : Shift Product right		0001 1000
3	1 : 0 ⇒ no operation		0001 1000
	2 : Shift Product right		0000 1100
4	1 : 0 ⇒ no operation		0000 1100
	2 : Shift Product right		0000 0110

Iteration	Step	Multiplicand	Product
0	Initial values	1000	0000 1001
1	1 : 1 ⇒ Product += Multiplicand		1000 1001
	2 : Shift Product right		0100 0100
2	1 : 0 ⇒ no operation		0100 0100
	2 : Shift Product right		0010 0010
3	1 : 0 ⇒ no operation		0010 0010
	2 : Shift Product right		0001 0001
4	1 : 1 ⇒ Product += Multiplicand		1001 0001
	2 : Shift Product right		0100 1000

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Two 32-bit registers for product
- HI : most-significant 32 bits
- LO : least-significant 32 bits

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mult, multu : 64-bit product in HI/LO

mfhi, mflo : Move from HI/LO to rd, Can test HI value to see if product overflows 32 bits

mul : Least-significant 32 bits of product → rd

mult rs, rt / multu rs, rt

mfhi rd / mflo rd

mul rd, rs, rt