Courgette: Add static method QuickDetect() to optimize program detection.

courgette/disassembler_win32_x64.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COURGETTE_DISASSEMBLER_WIN32_X64_H_
 #define COURGETTE_DISASSEMBLER_WIN32_X64_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "courgette/disassembler_win32.h"
 #include "courgette/image_utils.h"
 #include "courgette/types_win_pe.h"
 
 namespace courgette {
 
 class AssemblyProgram;
 
 class DisassemblerWin32X64 : public DisassemblerWin32 {
  public:
-  DisassemblerWin32X64(const void* start, size_t length);
+  // Returns true if a valid executable is detected using only quick checks.
+  static bool QuickDetect(const uint8_t* start, size_t length) {
+    return DisassemblerWin32::QuickDetect(start, length,
+                                          kImageNtOptionalHdr64Magic);
+  }
+
+  DisassemblerWin32X64(const uint8_t* start, size_t length);
   ~DisassemblerWin32X64() override = default;
 
   // Disassembler interfaces.
   RVA PointerToTargetRVA(const uint8_t* p) const override;
   ExecutableType kind() const override { return EXE_WIN_32_X64; }
 
   // (4) -> (5) (see AddressTranslator comment): Returns the RVA of the VA
   // specified by |address|, or kNoRVA if |address| lies outside of the image.
   RVA Address64ToRVA(uint64_t address) const;
 
  protected:
   // Disassembler interfaces.
   void ParseRel32RelocsFromSection(const Section* section) override;
   int AbsVAWidth() const override { return 8; }
   CheckBool EmitAbs(Label* label, AssemblyProgram* program) override;
   bool SupportsRelTableType(int type) const override {
     return type == 10;  // IMAGE_REL_BASED_DIR64
   }
   uint16_t OffsetOfDataDirectories() const override {
     return kOffsetOfDataDirectoryFromImageOptionalHeader64;
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DisassemblerWin32X64);
 };
 
 }  // namespace courgette
 
 #endif  // COURGETTE_DISASSEMBLER_WIN32_X64_H_