1 files changed, 52 insertions, 2 deletions
diff --git a/Lex/HeaderMap.cpp b/Lex/HeaderMap.cpp
index 5b9c4b0d23..ebcbc17f80 100644
--- a/Lex/HeaderMap.cpp
+++ b/Lex/HeaderMap.cpp
@@ -12,10 +12,60 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Lex/HeaderMap.h"
+#include "clang/Basic/FileManager.h"
+#include "llvm/ADT/scoped_ptr.h"
+#include "llvm/Support/DataTypes.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/MemoryBuffer.h"
 using namespace clang;
 
-const HeaderMap *HeaderMap::Create(const FileEntry *FE, std::string &ErrorInfo){
-  // FIXME: woot!
+enum {
+  HeaderMagicNumber = ('h' << 24) | ('m' << 16) | ('a' << 8) | 'p'
+};
+
+struct HMapHeader {
+  uint32_t Magic;           // Magic word, also indicates byte order.
+  uint16_t Version;         // Version number -- currently 1.
+  uint16_t Reserved;        // Reserved for future use - zero for now.
+  uint32_t StringsOffset;   // Offset to start of string pool.
+  uint32_t Count;           // Number of entries in the string table.
+  uint32_t Capacity;        // Number of buckets (always a power of 2).
+  uint32_t MaxValueLength;  // Length of longest result path (excluding nul).
+  // Strings follow the buckets, at StringsOffset.
+};
+
+
+/// HeaderMap::Create - This attempts to load the specified file as a header
+/// map.  If it doesn't look like a HeaderMap, it gives up and returns null.
+/// If it looks like a HeaderMap but is obviously corrupted, it puts a reason
+/// into the string error argument and returns null.
+const HeaderMap *HeaderMap::Create(const FileEntry *FE) {
+  // If the file is too small to be a header map, ignore it.
+  unsigned FileSize = FE->getSize();
+  if (FileSize <= sizeof(HMapHeader)) return 0;
+  
+  llvm::scoped_ptr<const llvm::MemoryBuffer> File( 
+    llvm::MemoryBuffer::getFile(FE->getName(), strlen(FE->getName()), 0,
+                                FE->getSize()));
+  if (File == 0) return 0;  // Unreadable file?
+  const char *FileStart = File->getBufferStart();
+
+  // We know the file is at least as big as the header, check it now.
+  const HMapHeader *Header = reinterpret_cast<const HMapHeader*>(FileStart);
+  
+  // Sniff it to see if it's a headermap.
+  if (Header->Version != 1 || Header->Reserved != 0)
+    return 0;
+  
+  // Check the magic number.
+  bool NeedsByteSwap;
+  if (Header->Magic == HeaderMagicNumber)
+    NeedsByteSwap = false;
+  else if (Header->Magic == llvm::ByteSwap_32(HeaderMagicNumber))
+    NeedsByteSwap = true;  // Mixed endianness headermap.
+  else 
+    return 0;  // Not a header map.
+  
   return 0; 
 }