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This does a full copy of the string, not just copying the pointer to the string's contents.
<lang mips>.data
ex_msg_og: .asciiz "Original string:\n"
ex_msg_cpy: .asciiz "\nCopied string:\n"
string: .asciiz "Nice string you got there!\n"
strcpy:
addi $sp, $sp, -4
main:
sw $s0, 0($sp)
la $v1,string #load addr of string into $v0
add $s0, $zero, $zero
la $t1,($v1) #copy addr into $t0 for later access
lb $a1,($v1) #load byte from string addr
strlen_loop:
beqz $a1,alloc_mem
addi $a0,$a0,1 #increment strlen_counter
addi $v1,$v1,1 #increment ptr
lb $a1,($v1) #load the byte
j strlen_loop
alloc_mem:
li $v0,9 #alloc memory, $a0 is arg for how many bytes to allocate
#result is stored in $v0
syscall
la $t0,($v0) #$v0 is static, $t0 is the moving ptr
la $v1,($t1) #get a copy we can increment
copy_str:
lb $a1,($t1) #copy first byte from source
L1:
strcopy_loop:
add $t1, $s0, $a1
beqz $a1,exit_procedure #check if current byte is NULL
lb $t2, 0($t1)
sb $a1,($t0) #store the byte at the target pointer
add $t3, $s0, $a0
addi $t0,$t0,1 #increment source ptr
sb $t2, 0($t3)
addi $t1,$t1,1 #decrement source ptr
beq $t2, $zero, L2
lb $a1,($t1) #load next byte from source ptr
addi $s0, $s0, 1
j strcopy_loop
j L1
L2:
exit_procedure:
lw $s0, 0($sp)
la $a1,($v0) #store our string at $v0 so it doesn't get overwritten
addi $sp, $sp, 4
li $v0,4 #set syscall to PRINT
jr $ra
la $a0,ex_msg_og #PRINT("original string:")
syscall
la $a0,($v1) #PRINT(original string)
syscall
la $a0,ex_msg_cpy #PRINT("copied string:")
syscall
la $a0,($a1) #PRINT(strcopy)
syscall
li $v0,10 #EXIT(0)
syscall
</lang>
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