text: //===-- llvm/Bitcode/ReaderWriter.h - Bitcode reader/writers ----*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This header defines interfaces to read and write LLVM bitcode files/streams.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_BITCODE_3_2_H
  #define LLVM_BITCODE_3_2_H
  
  #include <string>
  
  namespace llvm {
    class Module;
    class MemoryBuffer;
    class ModulePass;
    class BitstreamWriter;
    class LLVMContext;
    class raw_ostream;
  }  // End llvm namespace
  
  namespace llvm_3_2 {
    /// getLazyBitcodeModule - Read the header of the specified bitcode buffer
    /// and prepare for lazy deserialization of function bodies.  If successful,
    /// this takes ownership of 'buffer' and returns a non-null pointer.  On
    /// error, this returns null, *does not* take ownership of Buffer, and fills
    /// in *ErrMsg with an error description if ErrMsg is non-null.
    llvm::Module *getLazyBitcodeModule(llvm::MemoryBuffer *Buffer,
                                 llvm::LLVMContext& Context,
                                 std::string *ErrMsg = 0);
  
    /// getBitcodeTargetTriple - Read the header of the specified bitcode
    /// buffer and extract just the triple information. If successful,
    /// this returns a string and *does not* take ownership
    /// of 'buffer'. On error, this returns "", and fills in *ErrMsg
    /// if ErrMsg is non-null.
    std::string getBitcodeTargetTriple(llvm::MemoryBuffer *Buffer,
                                       llvm::LLVMContext& Context,
                                       std::string *ErrMsg = 0);
  
    /// ParseBitcodeFile - Read the specified bitcode file, returning the module.
    /// If an error occurs, this returns null and fills in *ErrMsg if it is
    /// non-null.  This method *never* takes ownership of Buffer.
    llvm::Module *ParseBitcodeFile(llvm::MemoryBuffer *Buffer, llvm::LLVMContext& Context,
                             std::string *ErrMsg = 0);
  
    /// WriteBitcodeToFile - Write the specified module to the specified
    /// raw output stream.  For streams where it matters, the given stream
    /// should be in "binary" mode.
    void WriteBitcodeToFile(const llvm::Module *M, llvm::raw_ostream &Out);
  
    /// createBitcodeWriterPass - Create and return a pass that writes the module
    /// to the specified ostream.
    llvm::ModulePass *createBitcodeWriterPass(llvm::raw_ostream &Str);
  
  
    /// isBitcodeWrapper - Return true if the given bytes are the magic bytes
    /// for an LLVM IR bitcode wrapper.
    ///
    static inline bool isBitcodeWrapper(const unsigned char *BufPtr,
                                        const unsigned char *BufEnd) {
      // See if you can find the hidden message in the magic bytes :-).
      // (Hint: it's a little-endian encoding.)
      return BufPtr != BufEnd &&
             BufPtr[0] == 0xDE &&
             BufPtr[1] == 0xC0 &&
             BufPtr[2] == 0x17 &&
             BufPtr[3] == 0x0B;
    }
  
    /// isRawBitcode - Return true if the given bytes are the magic bytes for
    /// raw LLVM IR bitcode (without a wrapper).
    ///
    static inline bool isRawBitcode(const unsigned char *BufPtr,
                                    const unsigned char *BufEnd) {
      // These bytes sort of have a hidden message, but it's not in
      // little-endian this time, and it's a little redundant.
      return BufPtr != BufEnd &&
             BufPtr[0] == 'B' &&
             BufPtr[1] == 'C' &&
             BufPtr[2] == 0xc0 &&
             BufPtr[3] == 0xde;
    }
  
    /// isBitcode - Return true if the given bytes are the magic bytes for
    /// LLVM IR bitcode, either with or without a wrapper.
    ///
    static bool inline isBitcode(const unsigned char *BufPtr,
                                 const unsigned char *BufEnd) {
      return isBitcodeWrapper(BufPtr, BufEnd) ||
             isRawBitcode(BufPtr, BufEnd);
    }
  
    /// SkipBitcodeWrapperHeader - Some systems wrap bc files with a special
    /// header for padding or other reasons.  The format of this header is:
    ///
    /// struct bc_header {
    ///   uint32_t Magic;         // 0x0B17C0DE
    ///   uint32_t Version;       // Version, currently always 0.
    ///   uint32_t BitcodeOffset; // Offset to traditional bitcode file.
    ///   uint32_t BitcodeSize;   // Size of traditional bitcode file.
    ///   ... potentially other gunk ...
    /// };
    ///
    /// This function is called when we find a file with a matching magic number.
    /// In this case, skip down to the subsection of the file that is actually a
    /// BC file.
    static inline bool SkipBitcodeWrapperHeader(unsigned char *&BufPtr,
                                                unsigned char *&BufEnd) {
      enum {
        KnownHeaderSize = 4*4,  // Size of header we read.
        OffsetField = 2*4,      // Offset in bytes to Offset field.
        SizeField = 3*4         // Offset in bytes to Size field.
      };
  
      // Must contain the header!
      if (BufEnd-BufPtr < KnownHeaderSize) return true;
  
      unsigned Offset = ( BufPtr[OffsetField  ]        |
                         (BufPtr[OffsetField+1] << 8)  |
                         (BufPtr[OffsetField+2] << 16) |
                         (BufPtr[OffsetField+3] << 24));
      unsigned Size   = ( BufPtr[SizeField    ]        |
                         (BufPtr[SizeField  +1] << 8)  |
                         (BufPtr[SizeField  +2] << 16) |
                         (BufPtr[SizeField  +3] << 24));
  
      // Verify that Offset+Size fits in the file.
      if (Offset+Size > unsigned(BufEnd-BufPtr))
        return true;
      BufPtr += Offset;
      BufEnd = BufPtr+Size;
      return false;
    }
  }  // End llvm_3_2 namespace
  
  #endif
  