STRCPY Implemented on MIPS32 - Step by Step Example

strcpy.asm

#STRCPY - MIPS32
#Author: Kelvin Nose :^)
#Date: 7/11/15
# void strcpy(char x[], char y[]){
#int i;
#i = 0;
#while((x[i] = y[i]) != '\0') /* copy and test byte */
#i+=1;
#}

strcpy:
	addi $sp, $sp, -4# allocate 4 bytes on stack
	sw $s0, 0($sp) # store s0 at offset 0 on stack
	
	add $s0, $zero, $zero # set i to 0, i = 0;
	
	while:
		add $t1, $a1, $s0 # load address of y[i], and sets to a temporal register
		lbu $t2, ($t1) # load byte unsigned, puts the character into y[i] // $t2 = y[i]
	
		add $t3, $s0, $a0 # load address of x[i], and sets to a temporal register
		sb $t2, ($t3) # store byte of y[i] to x[i] // x[i] = y[i]
	
		beq $t2, $zero, out_while # if x[i] == '\0' end while
		addi $s0, $s0, 1 # i++;
		j while # jumps to while
	
	out_while:
		lw $s0, 0($sp) # load contents of $s0 to its default value
		addi $sp, $sp, 4 # pop 4 bytes off stack
		jr $ra  # return with register address value to whoever called this