[MIPS] strcpy實作

strcpy:
    addi    $sp, $sp, -4        # adjust stack for 1 more item
    sw      $s0, 0($sp)         # save $s0
    add     $s0, $zero, $zero   # i = 0
L1:
    add     $t1, $s0, $a1       # address of y[i] in $t1
    lb      $t2, 0($t1)         # t2 = y[i]
    add     $t3, $s0, $a0       # address of x[i] in $t3
    sb      $t2, 0($t3)         # x[i] = y[i]
    beq     $t2, $zero, L2      # if y[i]==0, go to L2
    addi    $s0, $s0, 1         # i= i+1
    j       L1                  # go to L1
L2:
    lw      $s0, 0($sp)         # y[i] ==0; end of string, restore old $s0
    addi    $sp, $sp, 4         # pop 1 word off stack
    jr      $ra                 # return