Initial implementation of encoder

1 files changed, 67 insertions, 0 deletions

diff --git a/b32e.asm b/b32e.asm
new file mode 100644
index 0000000..b74d7d7
--- /dev/null
+++ b/b32e.asm
@@ -0,0 +1,67 @@
+section .data
+
+rfc4648 db 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567'
+
+section .bss
+
+input_buffer resb 5
+output_buffer resb 8
+
+section .text
+global _start
+
+; read_input
+; reads 5 bytes (40 bits) of input
+read_input:
+	; linux x64 read(stdin, input_buffer, 5)
+	mov rax, 0
+	mov rdi, 0
+	mov rsi, input_buffer
+	mov rdx, 5
+	syscall
+
+; write_output
+; writes the output buffer to stdout
+write_output:
+	; linux x64 write(stdout, output_buffer, 8)
+	mov rax, 1
+	mov rdi, 1
+	mov rsi, output_buffer
+	mov rdx, 5
+	syscall
+
+; b32e
+; encodes 40 bits (5 bytes) to 8 RFC4648 base32 characters
+; inputs: bl=5 bits
+; uses: rxb, rdx, r11
+b32e:
+	; set up outputs counter
+	xor r11, r11
+.loop:
+	; get 5 bits from the input
+	xor rbx, rbx
+	mov bl, byte [input_buffer]
+	and bl, 0x1f
+
+	; rshift the input buffer
+
+	; convert to base32
+	add rbx, rfc4648
+	mov dl, byte [rbx]
+	mov byte [output_buffer + r11], dl 
+
+	; increase counter
+	inc r11
+	cmp r11, 8
+	js .loop 
+
+
+_start:
+	nop
+	call read_input
+	call b32e
+
+	; linux x64 exit(0)
+	mov rax, 60
+	mov rdi, 0
+	syscall