What are the common MIPS instructions for data transfer and control flow?

1 Data transfer instructions

Data transfer instructions are used to move data between registers and memory. The most basic ones are load word (lw) and store word (sw), which load and store 32-bit words from and to memory addresses. For example, the instruction lw $t0, 8($s0) loads the word at the address stored in register $s0 plus 8 bytes into register $t0. Similarly, the instruction sw $t0, 12($s0) stores the word in register $t0 to the address stored in register $s0 plus 12 bytes. Other data transfer instructions include load byte (lb), store byte (sb), load upper immediate (lui), and load address (la).

2 Control flow instructions

Control flow instructions are used to alter the execution sequence of a program based on some conditions. The most common ones are branch and jump instructions, which change the value of the program counter (PC), which is the register that holds the address of the next instruction to execute. For example, the instruction beq $t0, $t1, label compares the values of registers $t0 and $t1, and if they are equal, it branches to the instruction at the label. Similarly, the instruction j label jumps unconditionally to the instruction at the label. Other control flow instructions include branch not equal (bne), branch on less than (blt), branch on greater than (bgt), and jump and link (jal).

3 Arithmetic and logic instructions

Arithmetic and logic instructions are used to perform calculations and operations on data stored in registers. The most common ones are add, subtract, multiply, divide, and, or, and not, which perform the corresponding operations on two or three operands and store the result in a destination register. For example, the instruction add $t0, $t1, $t2 adds the values of registers $t1 and $t2 and stores the result in register $t0. Similarly, the instruction not $t0, $t1 performs a bitwise complement on the value of register $t1 and stores the result in register $t0. Other arithmetic and logic instructions include add immediate (addi), subtract immediate (subi), multiply low (mult), multiply high (multu), divide (div), divide unsigned (divu), and shift left logical (sll).

4 Example program

To illustrate how these instructions work together, let's look at a simple MIPS program that calculates the factorial of a number n. The program assumes that n is stored in register $a0, and it uses registers $v0, $t0, and $t1 as temporary variables. The program outputs the factorial of n in register $v0.

# Factorial program

factorial: # label for the start of the program

li $v0, 1 # initialize $v0 to 1

move $t0, $a0 # copy $a0 to $t0

loop: # label for the loop body

beq $t0, 0, end # if $t0 is 0, branch to end

mul $v0, $v0, $t0 # multiply $v0 by $t0

subi $t0, $t0, 1 # decrement $t0 by 1

j loop # jump back to loop

end: # label for the end of the program

jr $ra # return to the caller