This is a description of the MIPS instruction set, their meanings, syntax, semantics, and bit encodings. The syntax given for each instruction refers to the assembly
language syntax supported by the MIPS assembler. Hyphens in the encoding indicate "don't care" bits which are not considered when an instruction is being decoded.
General purpose registers (GPRs) are indicated with a dollar sign ($). The words SWORD and UWORD refer to 32-bit signed and 32-bit unsigned data types, respectively.
The manner in which the processor executes an instruction and advances its program counters is as follows:
- execute the instruction at PC
- copy nPC to PC
- add 4 or the branch offset to nPC
This behaviour is indicated in the instruction specifications below. For brevity, the function advance_pc (int) is used in many of the instruction descriptions. This function is defined as follows:
void advance_pc (SWORD offset) { PC = nPC; nPC += offset; }
ALL immediate values should be sign extended. After that, you treat them as signed or unsigned 32 bit numbers. For the non-immediate instructions, the only difference between signed and unsigned instructions is that signed instructions can generate an overflow (which we aren't worried about in this lab).
| ADD | Add |
|---|---|
| Description | Adds two registers and stores the result in a register |
| Operation | $d = $s + $t; advance_pc (4); |
| Syntax | add $d, $s, $t |
| Encoding | 0000 00ss ssst tttt dddd d000 0010 0000 |
| ADDI | Add immediate |
|---|---|
| Description | Adds a register and a signed immediate value and stores the result in a register |
| Operation | $t = $s + imm; advance_pc (4); |
| Syntax | addi $t, $s, imm |
| Encoding | 0010 00ss ssst tttt iiii iiii iiii iiii |
| ADDIU | Add immediate unsigned |
|---|---|
| Description | Adds a register and an unsigned immediate value and stores the result in a register |
| Operation | $t = $s + imm; advance_pc (4); |
| Syntax | addiu $t, $s, imm |
| Encoding | 0010 01ss ssst tttt iiii iiii iiii iiii |
| ADDU | Add unsigned |
|---|---|
| Description | Adds two registers and stores the result in a register |
| Operation | $d = $s + $t; advance_pc (4); |
| Syntax | addu $d, $s, $t |
| Encoding | 0000 00ss ssst tttt dddd d000 0010 0001 |
| AND | Bitwise and |
|---|---|
| Description | Bitwise ands two registers and stores the result in a register |
| Operation | $d = $s & $t; advance_pc (4); |
| Syntax | and $d, $s, $t |
| Encoding | 0000 00ss ssst tttt dddd d000 0010 0100 |
| ANDI | Bitwise and immediate |
|---|---|
| Description | Bitwise ands a register and an immediate value and stores the result in a register |
| Operation | $t = $s & imm; advance_pc (4); |
| Syntax | andi $t, $s, imm |
| Encoding | 0011 00ss ssst tttt iiii iiii iiii iiii |
| BEQ | Branch on equal |
|---|---|
| Description | Branches if the two registers are equal |
| Operation | if $s == $t advance_pc (offset << 2)); else advance_pc (4); |
| Syntax | beq $s, $t, offset Encoding |
| BGEZ | Branch on greater than or equal to zero |
|---|---|
| Description | Branches if the register is greater than or equal to zero |
| Operation | if $s >= 0 advance_pc (offset << 2)); else advance_pc (4); |
| Syntax | bgez $s, offset |
| Encoding | 0000 01ss sss0 0001 iiii iiii iiii iiii |
| BGEZAL | Branch on greater than or equal to zero and link |
|---|---|
| Description | Branches if the register is greater than or equal to zero and saves the return address in $31 |
| Operation | if $s >= 0 $31 = PC + 8 (or nPC + 4); advance_pc (offset << 2)); else advance_pc (4); |
| Syntax | bgezal $s, offset |
| Encoding | 0000 01ss sss1 0001 iiii iiii iiii iiii |
| BGTZ | Branch on greater than zero |
|---|---|
| Description | Branches if the register is greater than zero |
| Operation | if $s > 0 advance_pc (offset << 2)); else advance_pc (4); |
| Syntax | bgtz $s, offset |
| Encoding | 0001 11ss sss0 0000 iiii iiii iiii iiii |
| BLEZ | Branch on less than or equal to zero |
|---|---|
| Description | Branches if the register is less than or equal to zero |
| Operation | if $s <= 0 advance_pc (offset << 2)); else advance_pc (4); |
| Syntax | blez $s, offset |
| Encoding | 0001 10ss sss0 0000 iiii iiii iiii iiii |
| BLTZ | Branch on less than zero |
|---|---|
| Description | Branches if the register is less than zero |
| Operation | if $s < 0 advance_pc (offset << 2)); else advance_pc (4); |
| Syntax | bltz $s, offset |
| Encoding | 0000 01ss sss0 0000 iiii iiii iiii iiii |
| BLTZAL | Branch on less than zero and link |
|---|---|
| Description | Branches if the register is less than zero and saves the return address in $31 |
| Operation | if $s < 0 $31 = PC + 8 (or nPC + 4); advance_pc (offset << 2)); else advance_pc (4); |
| Syntax | bltzal $s, offset |
| Encoding | 0000 01ss sss1 0000 iiii iiii iiii iiii |
| BNE | Branch on not equal |
|---|---|
| Description | Branches if the two registers are not equal |
| Operation | if $s != $t advance_pc (offset << 2)); else advance_pc (4); |
| Syntax | bne $s, $t, offset |
| Encoding | 0001 01ss ssst tttt iiii iiii iiii iiii |
| DIV | Divide |
|---|---|
| Description | Divides $s by $t and stores the quotient in $LO and the remainder in $HI |
| Operation | $LO = $s / $t; $HI = $s % $t; advance_pc (4); |
| Syntax | div $s, $t |
| Encoding | 0000 00ss ssst tttt 0000 0000 0001 1010 |
| DIVU | Divide unsigned |
|---|---|
| Description | Divides $s by $t and stores the quotient in $LO and the remainder in $HI |
| Operation | $LO = $s / $t; $HI = $s % $t; advance_pc (4); |
| Syntax | divu $s, $t |
| Encoding | 0000 00ss ssst tttt 0000 0000 0001 1011 |
| J | Jump |
|---|---|
| Description | Jumps to the calculated address |
| Operation | PC = nPC; nPC = (PC & 0xf0000000) | (target << 2); |
| Syntax | j target |
| Encoding | 0000 10ii iiii iiii iiii iiii iiii iiii |
| JAL | Jump and link |
|---|---|
| Description | Jumps to the calculated address and stores the return address in $31 |
| Operation | $31 = PC + 8 (or nPC + 4); PC = nPC; nPC = (PC & 0xf0000000) | (target << 2); |
| Syntax | jal target |
| Encoding | 0000 11ii iiii iiii iiii iiii iiii iiii |
| JR | Jump register |
|---|---|
| Description | Jump to the address contained in register $s |
| Operation | PC = nPC; nPC = $s; |
| Syntax | jr $s |
| Encoding | 0000 00ss sss0 0000 0000 0000 0000 1000 |
| LB | Load byte |
|---|---|
| Description | A byte is loaded into a register from the specified address. |
| Operation | $t = MEM[$s + offset]; advance_pc (4); |
| Syntax | lb $t, offset($s) |
| Encoding | 1000 00ss ssst tttt iiii iiii iiii iiii |
| LUI | Load upper immediate |
|---|---|
| Description | The immediate value is shifted left 16 bits and stored in the register. The lower 16 bits are zeroes. |
| Operation | $t = (imm << 16); advance_pc (4); |
| Syntax | lui $t, imm |
| Encoding | 0011 11-- ---t tttt iiii iiii iiii iiii |
| LW | Load word |
|---|---|
| Description | A word is loaded into a register from the specified address. |
| Operation | $t = MEM[$s + offset]; advance_pc (4); |
| Syntax | lw $t, offset($s) |
| Encoding | 1000 11ss ssst tttt iiii iiii iiii iiii |
| MFHI | Move from HI |
|---|---|
| Description | The contents of register HI are moved to the specified register. |
| Operation | $d = $HI; advance_pc (4); |
| Syntax | mfhi $d |
| Encoding | 0000 0000 0000 0000 dddd d000 0001 0000 |
| MFLO | Move from LO |
|---|---|
| Description | The contents of register LO are moved to the specified register. Operation |
| Syntax | mflo $d |
| Encoding | 0000 0000 0000 0000 dddd d000 0001 0010 |
| MULT | Multiply |
|---|---|
| Description | Multiplies $s by $t and stores the result in $LO. |
| Operation | $LO = $s * $t; advance_pc (4); |
| Syntax | mult $s, $t |
| Encoding | 0000 00ss ssst tttt 0000 0000 0001 1000 |
| MULTU | Multiply unsigned |
|---|---|
| Description | Multiplies $s by $t and stores the result in $LO. |
| Operation | $LO = $s * $t; advance_pc (4); |
| Syntax | multu $s, $t |
| Encoding | 0000 00ss ssst tttt 0000 0000 0001 1001 |
| NOOP | no operation |
|---|---|
| Description | Performs no operation. |
| Operation | advance_pc (4); |
| Syntax | noop |
| Encoding | 0000 0000 0000 0000 0000 0000 0000 0000 |
| Note | The encoding for a NOOP represents the instruction SLL $0, $0, 0 which has no side effects. In fact, nearly every instruction that has $0 as its destination register will have no side effect and can thus be considered a NOOP instruction. |
| OR | Bitwise or |
|---|---|
| Description | Bitwise logical ors two registers and stores the result in a register |
| Operation | $d = $s | $t; advance_pc (4); |
| Syntax | or $d, $s, $t |
| Encoding | 0000 00ss ssst tttt dddd d000 0010 0101 |
| ORI | Bitwise or immediate |
|---|---|
| Description | Bitwise ors a register and an immediate value and stores the result in a register |
| Operation | $t = $s | imm; advance_pc (4); |
| Syntax | ori $t, $s, imm |
| Encoding | 0011 01ss ssst tttt iiii iiii iiii iiii |
| SB | Store byte |
|---|---|
| Description | The least significant byte of $t is stored at the specified address. |
| Operation | MEM[$s + offset] = (0xff & $t); advance_pc (4); |
| Syntax | sb $t, offset($s) |
| Encoding | 1010 00ss ssst tttt iiii iiii iiii iiii |
| SLL | Shift left logical |
|---|---|
| Description | Shifts a register value left by the shift amount listed in the instruction and places the result in a third register. Zeroes are shifted in. |
| Operation | $d = $t << h; advance_pc (4); |
| Syntax | sll $d, $t, h |
| Encoding | 0000 00ss ssst tttt dddd dhhh hh00 0000 |
| SLLV | Shift left logical variable |
|---|---|
| Description | Shifts a register value left by the value in a second register and places the result in a third register. Zeroes are shifted in. |
| Operation | $d = $t << $s; advance_pc (4); |
| Syntax | sllv $d, $t, $s |
| Encoding | 0000 00ss ssst tttt dddd d--- --00 0100 |
| SLT | Set on less than (signed) |
|---|---|
| Description | If $s is less than $t, $d is set to one. It gets zero otherwise. |
| Operation | if $s < $t $d = 1; advance_pc (4); else $d = 0; advance_pc (4); |
| Syntax | slt $d, $s, $t |
| Encoding | 0000 00ss ssst tttt dddd d000 0010 1010 |
| SLTI | Set on less than immediate (signed) |
|---|---|
| Description | If $s is less than immediate, $t is set to one. It gets zero otherwise. |
| Operation | if $s < imm $t = 1; advance_pc (4); else $t = 0; advance_pc (4); |
| Syntax | slti $t, $s, imm |
| Encoding | 0010 10ss ssst tttt iiii iiii iiii iiii |
| SLTIU | Set on less than immediate unsigned |
|---|---|
| Description | If $s is less than the unsigned immediate, $t is set to one. It gets zero otherwise. |
| Operation | if $s < imm $t = 1; advance_pc (4); else $t = 0; advance_pc (4); |
| Syntax | sltiu $t, $s, imm |
| Encoding | 0010 11ss ssst tttt iiii iiii iiii iiii |
| SLTU | Set on less than unsigned |
|---|---|
| Description | If $s is less than $t, $d is set to one. It gets zero otherwise. |
| Operation | if $s < $t $d = 1; advance_pc (4); else $d = 0; advance_pc (4); |
| Syntax | sltu $d, $s, $t |
| Encoding | 0000 00ss ssst tttt dddd d000 0010 1011 |
| SRA | Shift right arithmetic |
|---|---|
| Description | Shifts a register value right by the shift amount (shamt) and places the value in the destination register. The sign bit is shifted in. |
| Operation | $d = $t >> h; advance_pc (4); |
| Syntax | sra $d, $t, h |
| Encoding | 0000 00-- ---t tttt dddd dhhh hh00 0011 |
| SRL | Shift right logical |
|---|---|
| Description | Shifts a register value right by the shift amount (shamt) and places the value in the destination register. Zeroes are shifted in. |
| Operation | $d = $t >> h; advance_pc (4); |
| Syntax | srl $d, $t, h |
| Encoding | 0000 00-- ---t tttt dddd dhhh hh00 0010 |
| SRLV | Shift right logical variable |
|---|---|
| Description | Shifts a register value right by the amount specified in $s and places the value in the destination register. Zeroes are shifted in. |
| Operation | $d = $t >> $s; advance_pc (4); |
| Syntax | srlv $d, $t, $s |
| Encoding | 0000 00ss ssst tttt dddd d000 0000 0110 |
| SUB | Subtract |
|---|---|
| Description | Subtracts two registers and stores the result in a register |
| Operation | $d = $s - $t; advance_pc (4); Syntax |
| Encoding | 0000 00ss ssst tttt dddd d000 0010 0010 |
| SUBU | Subtract unsigned |
|---|---|
| Description | Subtracts two registers and stores the result in a register |
| Operation | $d = $s - $t; advance_pc (4); |
| Syntax | subu $d, $s, $t |
| Encoding | 0000 00ss ssst tttt dddd d000 0010 0011 |
| SW | Store word |
|---|---|
| Description | The contents of $t is stored at the specified address. |
| Operation | MEM[$s + offset] = $t; advance_pc (4); |
| Syntax | sw $t, offset($s) |
| Encoding | 1010 11ss ssst tttt iiii iiii iiii iiii |
| SYSCALL | System call |
|---|---|
| Description | Generates a software interrupt. |
| Operation | advance_pc (4); |
| Syntax | syscall |
| Encoding | 0000 00-- ---- ---- ---- ---- --00 1100 |
| XOR | Bitwise exclusive or |
|---|---|
| Description | Exclusive ors two registers and stores the result in a register |
| Operation | $d = $s ^ $t; advance_pc (4); |
| Syntax | xor $d, $s, $t |
| Encoding | 0000 00ss ssst tttt dddd d--- --10 0110 |
| XORI | Bitwise exclusive or immediate |
|---|---|
| Description | Bitwise exclusive ors a register and an immediate value and stores the result in a register |
| Operation | $t = $s ^ imm; advance_pc (4); |
| Syntax | xori $t, $s, imm |
| Encoding | 0011 10ss ssst tttt iiii iiii iiii iiii |