1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
|
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, 8
syscall
ret
; b32d
; decodes 8 RFC4648 characters (without checking its validity!)
; uses reg: rax, rbx
; uses mem: input_buffer, output_buffer
b32d:
; reset rax (output)
xor rax, rax
; set downwards counter
mov bl, 8
.loop:
; get a character
mov bh, byte [output_buffer]
; if is padding, exit
cmp bh, 0x3d
je .exit
; shift rax of one byte
shl rax, 5
; insert the new 5 bits
or al, bh
; decrement counter
dec bl
jnz .loop
.exit:
; save output
mov [input_buffer], rax
ret
_start:
nop
.loop:
; read input
call read_input
; read nothing
cmp rax, 0
je .exit
; decode base32
call b32d
; print
call write_output
jmp .loop
.exit:
; linux x64 exit(0)
mov rax, 60
mov rdi, 0
syscall
|
