Disassembled instructions of the encoding algorithm of Half-Life
################################################################

(source: SWDS.DLL of the retail game version 1.1.1.0)

NOTE: when you run the dedicated server and want to debug SWDS.DLL,
      remember to add 0x5690000 to the offsets that you see in SWDS.DLL
      For example 0x00D2251C in runtime will be at offset 0x63b251c





* Referenced by a CALL at Addresses:
|:00D11A31   , :00D45E55   
|
:00D22460 55                      push ebp
:00D22461 8BEC                    mov ebp, esp
:00D22463 51                      push ecx
:00D22464 8B450C                  mov eax, dword ptr [ebp+0C]
:00D22467 24FC                    and al, FC
:00D22469 99                      cdq
:00D2246A 83E203                  and edx, 00000003
:00D2246D 03C2                    add eax, edx
:00D2246F C1F802                  sar eax, 02
:00D22472 85C0                    test eax, eax
:00D22474 7E6E                    jle 00D224E4
:00D22476 8B4D10                  mov ecx, dword ptr [ebp+10]
:00D22479 53                      push ebx
:00D2247A 8B5D08                  mov ebx, dword ptr [ebp+08]
:00D2247D 56                      push esi
:00D2247E 57                      push edi
:00D2247F 8D7D0C                  lea edi, dword ptr [ebp+0C]
:00D22482 F7D1                    not ecx
:00D22484 894DFC                  mov dword ptr [ebp-04], ecx
:00D22487 894508                  mov dword ptr [ebp+08], eax
:00D2248A F7DF                    neg edi
:00D2248C EB03                    jmp 00D22491

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:00D224DF(C)
|
:00D2248E 8B4DFC                  mov ecx, dword ptr [ebp-04]

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:00D2248C(U)
|
:00D22491 8B03                    mov eax, dword ptr [ebx]
:00D22493 33C1                    xor eax, ecx
:00D22495 50                      push eax
:00D22496 E8F5CAFFFF              call 00D1EF90
:00D2249B 83C404                  add esp, 00000004
:00D2249E 89450C                  mov dword ptr [ebp+0C], eax
:00D224A1 33C9                    xor ecx, ecx

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:00D224C8(C)
|
:00D224A3 8D740D0C                lea esi, dword ptr [ebp+ecx+0C]
:00D224A7 8AC1                    mov al, cl
:00D224A9 D2E0                    shl al, cl
:00D224AB 8D1437                  lea edx, dword ptr [edi+esi]
:00D224AE 83E20F                  and edx, 0000000F
:00D224B1 8A92886CDE00            mov dl, byte ptr [edx+00DE6C88]
:00D224B7 0AD0                    or dl, al
:00D224B9 8A06                    mov al, byte ptr [esi]
:00D224BB 0AD1                    or dl, cl
:00D224BD 80CAA5                  or dl, A5
:00D224C0 32C2                    xor al, dl
:00D224C2 41                      inc ecx
:00D224C3 83F904                  cmp ecx, 00000004
:00D224C6 8806                    mov byte ptr [esi], al
:00D224C8 7CD9                    jl 00D224A3
:00D224CA 8B450C                  mov eax, dword ptr [ebp+0C]
:00D224CD 8B7510                  mov esi, dword ptr [ebp+10]
:00D224D0 33C6                    xor eax, esi
:00D224D2 8903                    mov dword ptr [ebx], eax
:00D224D4 8B4508                  mov eax, dword ptr [ebp+08]
:00D224D7 83C304                  add ebx, 00000004
:00D224DA 47                      inc edi
:00D224DB 48                      dec eax
:00D224DC 894508                  mov dword ptr [ebp+08], eax
:00D224DF 75AD                    jne 00D2248E
:00D224E1 5F                      pop edi
:00D224E2 5E                      pop esi
:00D224E3 5B                      pop ebx

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:00D22474(C)
|
:00D224E4 8BE5                    mov esp, ebp
:00D224E6 5D                      pop ebp
:00D224E7 C3                      ret








The following is the function called at offset 0x00D22496
It is a simple byteswapping function:


:00D1EF90 55                      push ebp
:00D1EF91 8BEC                    mov ebp, esp
:00D1EF93 8B4D08                  mov ecx, dword ptr [ebp+08]
:00D1EF96 8BC1                    mov eax, ecx
:00D1EF98 8BD1                    mov edx, ecx
:00D1EF9A C1F808                  sar eax, 08
:00D1EF9D 81E2FF000000            and edx, 000000FF
:00D1EFA3 25FF000000              and eax, 000000FF
:00D1EFA8 C1E208                  shl edx, 08
:00D1EFAB 03C2                    add eax, edx
:00D1EFAD 8BD1                    mov edx, ecx
:00D1EFAF C1FA10                  sar edx, 10
:00D1EFB2 C1E008                  shl eax, 08
:00D1EFB5 81E2FF000000            and edx, 000000FF
:00D1EFBB 03C2                    add eax, edx
:00D1EFBD C1F918                  sar ecx, 18
:00D1EFC0 C1E008                  shl eax, 08
:00D1EFC3 81E1FF000000            and ecx, 000000FF
:00D1EFC9 03C1                    add eax, ecx
:00D1EFCB 5D                      pop ebp
:00D1EFCC C3                      ret