About how many significant bits do you expect in this product:
01001010 × 00010101
About 12 significant bits.
mfhi and mflo InstructionsTwo instructions move the result of a multiplication into a general purpose register:
mfhi d # d ← hi. Move From Hi
mflo d # d ← lo. Move From Lo
The hi and lo registers
cannot be used with any of the other arithmetic or logic
instructions.
If you want to do something with a product, it must first
be moved to a general purpose register.
However there is a further complication on MIPS hardware:
Rule:
The next two instructions after a mflo
or mfhi must not be a multiply or a divide instruction.
The reason for this involves the way the MIPS pipeline works.
On the SPIM simulator this rule does not matter (but on actual hardware it does.)
Must you move the result of a multiplication into a general purpose register before you start another multiply operation?