128-bit programming challenge

Here's my entry for the 128-bit programming challenge. Not a single lookup table in there. The resulting stripped binary is down to exactly 500 bytes.

; nasm -f elf hex.asm
; ld hex.o

section .text
global  _start
_start:
       mov     ecx,10h
       mov     esi,hex
       mov     edi,buffer
lp:
       movzx   eax,byte [esi]
       mov     ah,al
       and     al,0fh
       cmp     al,0ah
       sbb     al,69h
       das
       mov     [edi+1],al
       shr     ax,12
       cmp     al,0ah
       sbb     al,69h
       das
       mov     [edi],al
       mov     [edi+2],byte 20h
       add     edi,3
       inc     esi
       loop    lp
       mov     [edi],byte 0ah
       mov     ecx,buffer
       mov     eax,4
lp2:
       xor     ebx,ebx
       inc     ebx
       mov     edx,31h
       int     80h
       mov     eax,1
       mov     ebx,0
       int     80h
hex:
       or      ecx,edi
       adc     [edx],eax
       popfd
       jz      lp2
       pop     ebx
       fadd    dword [ecx+56h]
       lds     esp,[ebx+56h]
       mov     al,al
section .bss
       buffer  resb 31h