diff options
| -rw-r--r-- | b32e.asm | 99 |
1 files changed, 56 insertions, 43 deletions
@@ -12,63 +12,76 @@ 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 + ; 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 + ; 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 -; inputs: bl=5 bits -; uses: rxb, rdx, r11 +; uses reg: rbx, rdx, r11 +; uses mem: input_buffer, output_buffer b32e: - ; set up outputs counter - xor r11, r11 + ; set up output counter + xor r11, r11 + .loop: - ; get 5 bits from the input - xor rbx, rbx - mov bl, byte [input_buffer] - ; mask and shift to convert to a number 0 ~ 32 - and bl, 0xf8 - shr bl, 3 + ; 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 - ; rshift the input buffer - shl qword [input_buffer], 5 + ; increase counter + inc r11 - ; convert to base32 - add rbx, rfc4648 - mov dl, byte [rbx] - mov byte [output_buffer + r11], dl + ; check counter + ; when the counter reaches 8 it means that 8 characters (40 bits) + ; have been processed and written + cmp r11, 8 + js .loop - ; increase counter - inc r11 - cmp r11, 8 - js .loop - ret + ret _start: - nop - call read_input - call b32e - call write_output + nop + call read_input + call b32e + call write_output .exit: - ; linux x64 exit(0) - mov rax, 60 - mov rdi, 0 - syscall + ; linux x64 exit(0) + mov rax, 60 + mov rdi, 0 + syscall |