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%define BUFFSIZE    256
global _start

section .data
error   db  "Please enter one or less parameters.", 0xA, 0x0
errlen  equ     $-error

section .bss
buffer  resb    BUFFSIZE

section .text
_start:
    ; test for arguments
    cmp qword[rsp], 0x2
stop1:
    jl  _cliread
    jg  _error

    ; calculate length of string
    mov     rdi, [rsp+16]   ; destination index
    xor     rcx, rcx        ; rcx = -1
    not     rcx             ; rcx = -1
    xor     al,al
    cld                     ; process String from lowest to highest address
                            ; (clear diretion flag)
    ;SCASB: Compare AL with byte at RDI then set status flags.
    ;REPNZ: Repeats a string instruction RCX times or until ZF = 1
    repnz   scasb           ; get the string length (dec rcx through NUL)
    not     rcx             ; rev all bits of negative results in absolute value
    dec     rcx             ; -1 to skip the null-terminator, rcx contains
                            ; length
    ; initialize source for write
    mov     rsi, [rsp+16]   ; read from [rsp+16]
    mov     rdx, rcx        ; read rcx bytes
    jmp     _cliwrite

_cliread:
    ; read (0) from stdin (0)
    mov rax, 0
    mov rdi, 0
    mov rsi, buffer
    mov rdx, BUFFSIZE
    syscall
    ; initialize source for write
    mov rsi, buffer
    mov rdx, BUFFSIZE
    jmp _cliwrite

_error:
    ; initialize source for write
    mov rsi, error
    mov rdx, errlen

_cliwrite:
    ; write (1) to stdout (1)
    mov rax, 1
    mov rdi, 1
    syscall

_end:
    mov rax, 60
    mov rdi, 1
    syscall