section .data

rfc4648 db 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567'

section .bss

input_buffer resb 8
output_buffer resb 8

section .text
global _start

; read_input
; reads 5 bytes (40 bits) of input
; uses reg: rax, rdi, rsi, rdx
; uses mem: input_buffer
read_input:
    ; linux x64 read(stdin, input_buffer, 5)
    mov rax, 0
    mov rdi, 0
    mov rsi, input_buffer
    mov rdx, 5
    syscall
    ret

; write_output
; writes the output buffer to stdout
; uses reg: rax, rdi, rsi, rdx
; uses mem: output_buffer(ro)
write_output:
    ; linux x64 write(stdout, output_buffer, 8)
    mov rax, 1
    mov rdi, 1
    mov rsi, output_buffer
    mov rdx, 5
    syscall
    ret

; b32e
; encodes 40 bits (5 bytes) to 8 RFC4648 base32 characters
; uses reg: rbx, rdx, r11
; uses mem: input_buffer, output_buffer
b32e:
    ; set up output counter
    xor r11, r11

.loop:
    ; clear rbx
    xor rbx, rbx

    ; get a byte from the input
    mov bl, byte [input_buffer]

    ; mask and shift to get 5 bits which is a number in 0 ~ 31
    and bl, 0xf8
    shr bl, 3

    ; rshift the input buffer
    shr qword [input_buffer], 5

    ; convert to base32
    add rbx, rfc4648
    mov dl, byte [rbx]
    mov [output_buffer + r11], dl 

    ; increase counter
    inc r11

    ; check counter
    ; when the counter reaches 8 it means that 8 characters (40 bits)
    ; have been processed and written
    cmp r11, 8
    js .loop 

    ret


_start:
    nop
    call read_input
    call b32e
    call write_output
.exit:
    ; linux x64 exit(0)
    mov rax, 60
    mov rdi, 0
    syscall