arithmetic instructions

Complete

Summary

Add

  • R-type
mips
add dest, src1, src2 # dest <- src1 + src2

Add immediate

  • I-type
mips
addi dest, src, n # dest <- src + n

n will be a 16-bit 2s complement number, sign extended to 32-bit

Subtract

  • R-type
mips
sub dest, src1, src2  # dest <- src1 - src2

there is no subi instruction, use addi with the 2s complement for -n

Move

  • pseudo-instruction
mips
move dest, src # dest <- src

# is translated to
add dest, src, $zero # dest <- src + 0

Concept

Register instructions(R-type)

  • three registers

Immediate instructions(I-type)

  • two registers and one immediate value
  • immediate value is a 16-bit number

the three types of MIPS instructions are R-type, I-type and J-type

Pseudo-instructions

  • syntatic sugar, provides convenience
  • translated to real instructions before being assembled

Application

Complex arithmetic operations

c
e = (a + b) - (c + d);
mips
# variable mapping
# a -> $s0
# b -> $s1
# c -> $s2
# d -> $s3
# e -> $s4
add $t0, $s0, $s1 # $t0 <- a + b
add $t1, $s2, $s3 # $t1 <- c + d
sub $s4, $t0, $t1 #