Arithmetic: I-type
001000 01000 01001  01010  00000 100001
b31-26 b25-21 b20-16 b15-0
opcode    $rs      $rt immediate
addi
addi $rt, $rs, immed    # R[t] <- R[s] + immed
I-type
add value given in the instruction to contents of a register
how many bits in the value?
sign bit extended
note $rt is destination
what about subi?
opcode: 8
addiu
unsigned add, without overflow
opcode: 9
How would we increment the value of a register by a constant?