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:

• true, goes to the given label
• false, goes to the next instruction (i.e. it does nothing)

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.
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