Here are tables of common MIPS instructions and what they do. If you want some in-context examples of when you’d use them, see the cookbook.

Arithmetic and Bitwise Instructions

All arithmetic and bitwise instructions can be written in two ways:

  1. add t0, t1, t2
    • adds two registers and puts the result in a third register.
    • this does t0 = t1 + t2
  2. add t0, t1, 4
    • adds a register and a constant and puts the result in a second register.
    • this does t0 = t1 + 4

The i means “immediate,” since numbers inside instructions are called immediates.

Sometimes for this second form, you will see it written like addi or subi. These are completely equivalent, just a different name for the same instruction.

Mnemonic Operation Description
neg a, b a = -b gives the negative of b.
add a, b, c a = b + c adds signed numbers.
sub a, b, c a = b - c subtracts signed numbers.
mul a, b, c a = b * c gives low 32 bits of signed multiplication.
div a, b, c a = b / c gives quotient of signed division.
rem a, b, c a = b % c gives remainder of signed division.
addu a, b, c a = b + c adds unsigned numbers.
subu a, b, c a = b - c subtracts unsigned numbers.
mulu a, b, c a = b * c gives low 32 bits of unsigned multiplication.
divu a, b, c a = b / c gives quotient of unsigned division.
remu a, b, c a = b % c gives remainder of unsigned division.
mfhi a a = HI after mul, gives high 32 bits. after div, gives remainder.
mflo a a = LO after mul, gives low 32 bits. after div, gives quotient.
not a, b a = ~b gives the bitwise complement of b (all bits flipped).
and a, b, c a = b & c bitwise ANDs numbers.
or a, b, c a = b | c bitwise ORs numbers.
xor a, b, c a = b ^ c bitwise XORs numbers.

Shift Instructions

MIPS decided to implement shifts a little differently than the rest of the arithmetic and bitwise instructions.

Mnemonic Operation Description
sll a, b, imm a = b << imm shift left by a constant amount.
srl a, b, imm a = b >>> imm shift right unsigned (logical) by a constant amount.
sra a, b, imm a = b >> imm shift right arithmetic by a constant amount.
sllv a, b, reg a = b << reg shift left by the amount in a register.
srlv a, b, reg a = b >>> reg shift right unsigned (logical) by the amount in a register.
srav a, b, reg a = b >> reg shift right arithmetic by the amount in a register.

Data Transfer Instructions

There are two “load” instructions which do not access memory. Also, move does not move, it copies. THAT’S LIFE.

Mnemonic Operation Description
li a, imm a = imm put a constant value into a register.
la a, label a = &label put the address that a label points to into a register.
move a, b a = b copy value from one register to another.

The rest of the load/store instructions always access memory. All of these instructions can be written in three different ways:

  1. lw t0, var
    • copies a word (32-bit value) from the memory variable var into register t0
    • var must have been declared as something like:
        .data
        var: .word 0
      
  2. lw t0, (t1)
    • copies a word from the memory address given by t1 into register t0
  3. lw t0, 4(t1)
    • copies a word from the memory address given by t1 + 4 into register t0

REMEMBER: stores copy values FROM registers TO memory. So FROM the left side TO the address on the right side.

Mnemonic Operation Description
lw reg, addr reg = MEM[addr] loads the 4 bytes at addr as a 32-bit value into reg.
lh reg, addr reg = sxt(MEM[addr]) loads the 2 bytes at addr as a signed 16-bit value into reg.
lb reg, addr reg = sxt(MEM[addr]) loads the 1 byte at addr as a signed 8-bit value into reg.
lhu reg, addr reg = zxt(MEM[addr]) loads the 2 bytes at addr as an unsigned 16-bit value into reg.
lbu reg, addr reg = zxt(MEM[addr]) loads the 1 byte at addr as an unsigned 8-bit value into reg.
sw reg, addr MEM[addr] = reg stores the value of reg into memory as 4 bytes starting at addr.
sh reg, addr MEM[addr] = lo16(reg) stores the low 16 bits of reg into memory as 2 bytes starting at addr.
sb reg, addr MEM[addr] = lo8(reg) stores the low 8 bits of reg into memory as 1 byte at addr.

Last, there are two stack (pseudo-)instructions which are used to save and restore values in functions:

Mnemonic Operation Description
push reg sp -= 4; MEM[sp] = reg pushes the value of reg onto the call stack
pop reg reg = MEM[sp]; sp += 4 pops the top call stack value and puts it into reg

Unconditional Control Flow Instructions

These always change the PC to a new location.

Mnemonic Operation Description
j label PC = label goes to the instruction at label.
jal label ra = PC + 4; PC = label function call to label. stores return address in ra.
jr reg PC = reg goes to the instruction whose address is in reg, often ra.
syscall ---> runs the system call function whose number is in v0.

Conditional Control Flow Instructions

All these instructions check the given condition, and if it’s:

Also, all of these instructions can be written two ways:

  1. blt t0, t1, label
    • compares two registers (sees if t0 < t1)
  2. blt t0, 10, label
    • compares a register to a constant (sees if t0 < 10)
Mnemonic Operation Description
beq a, b, label if(a == b) { PC = label } if a is equal to b, goes to label .
bne a, b, label if(a != b) { PC = label } if a is NOT equal to b, goes to label .
blt a, b, label if(a < b) { PC = label } if a is less than b, goes to label .
ble a, b, label if(a <= b) { PC = label } if a is less than or equal to b, goes to label .
bgt a, b, label if(a > b) { PC = label } if a is greater than b, goes to label .
bge a, b, label if(a >= b) { PC = label } if a is greater than or equal to b, goes to label .
bltu a, b, label if(a < b) { PC = label } same as blt but does an unsigned comparison.
bleu a, b, label if(a <= b) { PC = label } same as ble but does an unsigned comparison.
bgtu a, b, label if(a > b) { PC = label } same as bgt but does an unsigned comparison.
bgeu a, b, label if(a >= b) { PC = label } same as bge but does an unsigned comparison.