diff --git a/tier1/undiff.cpp b/tier1/undiff.cpp
deleted file mode 100644
index 17505b27..00000000
--- a/tier1/undiff.cpp
+++ /dev/null
@@ -1,94 +0,0 @@
-//========= Copyright © 1996-2005, Valve Corporation, All rights reserved. ============//
-//
-// UnDiff - Apply difference block
-//
-//=============================================================================//
-
-#include "tier0/platform.h"
-#include "tier0/dbg.h"
-#include "tier1/diff.h"
-#include "mathlib/mathlib.h"
-
-// memdbgon must be the last include file in a .cpp file!!!
-#include "tier0/memdbgon.h"
-
-void ApplyDiffs(uint8 const *OldBlock, uint8 const *DiffList,
-                int OldSize, int DiffListSize, int &ResultListSize,uint8 *Output,uint32 OutSize)
-{
-  uint8 const *copy_src=OldBlock;
-  uint8 const *end_of_diff_list=DiffList+DiffListSize;
-  uint8 const *obuf=Output;
-  while(DiffList<end_of_diff_list)
-  {
-    //  printf("dptr=%x ",DiffList-d);
-    uint8 op=*(DiffList++);
-    if (op==0)
-    {
-      uint16 copy_sz=DiffList[0]+256*DiffList[1];
-      int copy_ofs=DiffList[2]+DiffList[3]*256;
-      if (copy_ofs>32767)
-        copy_ofs|=0xffff0000;
-    //    printf("long cp from %x to %x len=%d\n", copy_src+copy_ofs-OldBlock,Output-obuf,copy_sz);
-      
-      memcpy(Output,copy_src+copy_ofs,copy_sz);
-      Output+=copy_sz;
-      copy_src=copy_src+copy_ofs+copy_sz;
-      DiffList+=4;
-    }
-    else
-    {
-      if (op & 0x80)
-      {
-        int copy_sz=op & 0x7f;
-        int copy_ofs;
-        if (copy_sz==0)
-        {
-          copy_sz=DiffList[0];
-          if (copy_sz==0)
-          {
-            // big raw copy
-            copy_sz=DiffList[1]+256*DiffList[2]+65536*DiffList[3];
-            memcpy(Output,DiffList+4,copy_sz);
-    //          printf("big rawcopy to %x len=%d\n", Output-obuf,copy_sz);
-            
-            DiffList+=copy_sz+4;
-            Output+=copy_sz;
-          }
-          else
-          {
-            copy_ofs=DiffList[1]+(DiffList[2]*256);
-            if (copy_ofs>32767)
-              copy_ofs|=0xffff0000;
-    //          printf("long ofs cp from %x to %x len=%d\n", copy_src+copy_ofs-OldBlock,Output-obuf,copy_sz);
-            
-            memcpy(Output,copy_src+copy_ofs,copy_sz);
-            Output+=copy_sz;
-            copy_src=copy_src+copy_ofs+copy_sz;
-            DiffList+=3;
-          }
-        }
-        else
-        {
-          copy_ofs=DiffList[0];
-          if (copy_ofs>127)
-            copy_ofs|=0xffffff80;
-    //        printf("cp from %x to %x len=%d\n", copy_src+copy_ofs-OldBlock,Output-obuf,copy_sz);
-          
-          memcpy(Output,copy_src+copy_ofs,copy_sz);
-          Output+=copy_sz;
-          copy_src=copy_src+copy_ofs+copy_sz;
-          DiffList++;
-        }
-      }
-      else
-      {
-    //      printf("raw copy %d to %x\n",op & 127,Output-obuf);
-        memcpy(Output,DiffList,op & 127);
-        Output+=op & 127;
-        DiffList+=(op & 127);
-      }
-    }
-  }
-  ResultListSize=Output-obuf;
-  
-}