ping21

section .data
    msg1 db 'cong'
    msg1Len equ $-msg1

section .bss
    buff resb 50

section .text
    global _start

_start:
    mov eax, 3
    mov ebx, 0
    mov ecx, buff
    mov edx, 50
    int 80h

    mov eax, buff
    mov ecx, -1

    .loop:
        inc ecx
        cmp byte [eax + ecx], 0
        jne .loop

    ;mov ecx, 4
    dec ecx
    mov eax, buff
    mov esi, eax  ; esi points to start of string
    add eax, ecx
    mov edi, eax
    dec edi       ; edi points to end of string
    shr ecx, 1    ; ecx is count (length/2)
    jz _done       ; if string is 0 or 1 characters long, done
    reverseLoop:
    mov al, [esi] ; load characters
    mov bl, [edi]
    mov [esi], bl ; and swap
    mov [edi], al
    inc esi       ; adjust pointers
    dec edi
    dec ecx       ; and loop
    jnz reverseLoop

    mov eax, 4
    mov ebx, 1
    mov ecx, buff
    mov edx, 4
    int 80h
_done:
    mov eax, 1
    mov ebx, 0
    int 80h