Beginnings of a DNS resolver

diff --git a/dnsresolv.inc b/dnsresolv.inc
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+; -*- fundamental -*-
+; -----------------------------------------------------------------------
+;   
+;   Copyright 2004 H. Peter Anvin - All Rights Reserved
+;
+;   This program is free software; you can redistribute it and/or modify
+;   it under the terms of the GNU General Public License as published by
+;   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
+;   Bostom MA 02111-1307, USA; either version 2 of the License, or
+;   (at your option) any later version; incorporated herein by reference.
+;
+; -----------------------------------------------------------------------
+
+;
+; dnsresolv.inc
+;
+; Very simple DNS resolver (assumes recursion-enabled DNS server;
+; this should be the normal thing for client-serving DNS servers.)
+;
+
+               section .text
+
+;
+; Turn a string in DS:SI into a DNS "label set" in ES:DI.
+; On return, DI points to the first byte after the label set.
+;
+mangle_dnsname:
+               push ax
+               push cx
+               xor cx,cx
+.getbyte:
+               jcxz .nostart   
+.gotstart:
+               lodsb
+               and al,al
+               jz .endstring
+               cmp al,'.'
+               je .isdot
+               inc byte [es:cx]
+               stosb
+               jmp .getbyte
+.nostart:
+               xor al,al
+               mov cx,di
+               stosb
+               jmp .gotstart
+.isdot:
+               xor cx,cx
+               jmp .getbyte
+.endstring:
+               mov al,[es:cx]
+               and al,al
+               jz .done
+               xor al,al
+               stosb
+.done:
+               pop cx
+               pop ax
+               ret
+
+;
+; Compare two sets of DNS labels, in DS:SI and DS:DI; the one in SI
+; is allowed pointers relative to a packet address in BX.
+;
+; Assumes DS == ES.  ZF = 1 if same; no registers changed.
+;
+dns_compare:
+               pusha
+
+.label:
+               lodsb
+               cmp al,0C0h
+               jb .noptr
+               and al,03Fh
+               mov ah,al
+               lodsb
+               mov si,bx
+               add si,ax
+               jmp .label
+.noptr:
+               cmp al,[di]
+               jne .done                       ; Mismatch
+               inc di
+               movzx cx,al                     ; End label?
+               and cx,cx                       ; ZF = 1 if match
+               jz .done
+               
+               ; We have a string of bytes that need to match now
+               repe cmpsb
+               jz .label
+
+.done:
+               popa
+               ret
+
+;
+; Skip past a DNS label set in DS:SI.
+;
+dns_skiplabel:
+               push ax
+               xor ax,ax                       ; AH == 0
+.loop:
+               lodsb
+               cmp al,0C0h
+               jae .ptr
+               and al,al
+               jz .done
+               add si,ax
+               jmp .loop
+.ptr:
+               inc si
+.done:
+               pop ax
+               ret
+