Instructions: Data Transfer

Byte operations

lb  $rt, offset($rs)

Load sign-extended byte

from memory location to register

lbu $rt, offset($rs)

Load zero-extended (unsigned) byte

from memory location to register

sb  $rt, offset($rs)

Store the least significant byte of a

register to memory location

What about sbu?

For lb, the address is computed the same way as lw,

but the address does not have to be word aligned.

Addr <-- R[s] + (IR15)16::IR15-0

R[t] <-- (M1[ Addr ]7)24::M1[ Addr ]

Since the value is interpreted as 2C, the fetched byte is sign-extended to 32 bits.

lbu is just like lb except the byte is zero-extended in the register

sb is similar to sw:

M1[ Addr ] <-- R[t]7-0

The least significant byte of register t is copied to the address in memory.

Do we really need to have separate instructions to load, store bytes?