zip: avoid insanly slow zip file listing due to cache thrashing

Zip file list extractor kept seeking back and forth from central
file list to header in front of actual file data, causing all
caches to be flushed on read.

Avoid cache thrashing by first reading all central headers, then
extracting data from file headers (technically this could even be
skipped when only a file list is wanted)

xbmc/filesystem/ZipManager.cpp

@@ -82,7 +82,6 @@ bool CZipManager::GetZipList(const CStdString& strPath, vector<SZipEntry>& items
     return false;
   }
 
-  SZipEntry ze;
   unsigned int hdr;
   mFile.Read(&hdr, 4);
   if( Endian_SwapLE32(hdr) != ZIP_LOCAL_HEADER )
@@ -168,6 +167,7 @@ bool CZipManager::GetZipList(const CStdString& strPath, vector<SZipEntry>& items
   char temp[CHDR_SIZE];
   while (mFile.GetPosition() < cdirOffset + cdirSize)
   {
+    SZipEntry ze;
     mFile.Read(temp,CHDR_SIZE);
     readCHeader(temp, ze);
     if (ze.header != ZIP_CENTRAL_HEADER)
@@ -185,9 +185,16 @@ bool CZipManager::GetZipList(const CStdString& strPath, vector<SZipEntry>& items
     ZeroMemory(ze.name, 255);
     strncpy(ze.name, strName.c_str(), strName.size()>254 ? 254 : strName.size());
 
-    // Save the current position
-    int64_t savePos = mFile.GetPosition();
+    // Jump after central file header extra field and file comment
+    mFile.Seek(ze.eclength + ze.clength,SEEK_CUR);
+
+    items.push_back(ze);
+  }
 
+  /* go through list and figure out file header lengths */
+  for(vector<SZipEntry>::iterator it = items.begin(); it != items.end(); ++it)
+  {
+    SZipEntry& ze = *it;
     // Go to the local file header to get the extra field length
     // !! local header extra field length != central file header extra field length !!
     mFile.Seek(ze.lhdrOffset+28,SEEK_SET);
@@ -197,10 +204,6 @@ bool CZipManager::GetZipList(const CStdString& strPath, vector<SZipEntry>& items
     // Compressed data offset = local header offset + size of local header + filename length + local file header extra field length
     ze.offset = ze.lhdrOffset + LHDR_SIZE + ze.flength + ze.elength;
 
-    // Jump after central file header extra field and file comment
-    mFile.Seek(savePos + ze.eclength + ze.clength,SEEK_SET);
-
-    items.push_back(ze);
   }
 
   mZipMap.insert(make_pair(strFile,items));