palindrome check

#palindrome
.data
    str: .string "madam" # string to check
.text
    la x3,str
    li sp,0x500 # initialize stack pointer

# block below loads string to stack (LIFO)
rpt:
    lbu x4,0(x3)
    beq x4,x0,retr
    addi x8,x8,1
    sb x4,-1(sp)
    addi x3,x3,1
    addi sp,sp,-1
    j rpt
retr:
    la x3,str
    addi x1,x0,1 # set result to 1
next:
    lbu x6,0(sp)
    lbu x4,0(x3)
    bne x4,x6,exit # exits if palindrome check fails
    addi sp,sp,1
    addi,x3,x3,1
    addi x8,x8,-1
    beq x8,x0, last # check loop counter
    j next
exit:
    addi x1,x0,0 # sets result to 0l
    j last
last:
    nop