Strncpy in MIPS has a weird behavior

问题:

Here's my code for strncpy. In theory it should work, but when I run tests on it it gives out garbage.

Arguments:
  $a0 = pointer to destination array
  $a1 = source string
  $a2 = number of characters to copy

Returns: the destination array

 strncpy:   
        beqz $a2, out
        lb $t0, 0($a1)      #load byte
        beqz $t0 out 
        subiu $a2, $a2, 1
        sb $t0, 0($a0)
        addiu $a0, $a0, 1
        addiu $a1, $a1, 1
        j strncpy
out:
    lb $0 0($a0)
        move $v0 $a0
        jr $ra

回答1:

coppy original address of destination array ($a0) and load it in "out:" in $a0->$v0. (in your version you would always get the char behind the last insert... in addition to the above mentioned problem in out:)

addi $a3 $a0 0

strncpy:
(...)

out:
move $a0 $a3
move $v0 $a0