More work on the DNS resolver

diff --git a/dnsresolv.inc b/dnsresolv.inc
index a8a5192..d8d1ff0 100644 (file)
--- a/dnsresolv.inc
+++ b/dnsresolv.inc
@@ -24,45 +24,42 @@
 ; 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.
 ;
+; Assumes DS == ES.  Change references to [bx] to [es:bx] to remove
+; that assumption.
+;
 mangle_dnsname:
                push ax
-               push cx
-               xor cx,cx
+               push bx
+.nostart:
+.isdot:
+               xor al,al
+               mov bx,di
+               stosb
 .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
+               inc byte [bx]
                stosb
-               jmp .gotstart
-.isdot:
-               xor cx,cx
                jmp .getbyte
 .endstring:
-               mov al,[es:cx]
-               and al,al
+               cmp byte [bx],0
                jz .done
                xor al,al
                stosb
 .done:
-               pop cx
+               pop bx
                pop ax
                ret
 
 ;
-; Compare two sets of DNS labels, in DS:SI and DS:DI; the one in SI
+; Compare two sets of DNS labels, in DS:SI and ES: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.
+; (Note: change reference to [di] to [es:di] to remove DS == ES assumption)
 ;
 dns_compare:
                pusha
@@ -71,8 +68,8 @@ dns_compare:
                lodsb
                cmp al,0C0h
                jb .noptr
-               and al,03Fh
-               mov ah,al
+               and al,03Fh                     ; Get pointer value
+               mov ah,al                       ; ... in network byte order!
                lodsb
                mov si,bx
                add si,ax
@@ -101,14 +98,14 @@ dns_skiplabel:
                xor ax,ax                       ; AH == 0
 .loop:
                lodsb
-               cmp al,0C0h
+               cmp al,0C0h                     ; Pointer?
                jae .ptr
                and al,al
                jz .done
                add si,ax
                jmp .loop
 .ptr:
-               inc si
+               inc si                          ; Pointer is two bytes
 .done:
                pop ax
                ret