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

courgette/disassembler_win32.cc

Index: courgette/disassembler_win32.cc
diff --git a/courgette/disassembler_win32.cc b/courgette/disassembler_win32.cc
index 029284e46974818f3482fd437bff28660fde2b17..1c7008cbd4f928b44ffe8589ae8ddd96c3e4a917 100644
--- a/courgette/disassembler_win32.cc
+++ b/courgette/disassembler_win32.cc
@@ -653,4 +653,36 @@ bool DisassemblerWin32::ReadDataDirectory(int index,
   }
 }
 
+bool DisassemblerWin32::QuickDetects(const uint8_t* start,

[huangs, 2016/06/10 21:10:22]

Move to line 341 for consistent ordering with header.

[etiennep, 2016/06/13 17:50:21]

Done.

+                                     size_t length,
+                                     uint16_t magic) {
+  if (length < kOffsetOfFileAddressOfNewExeHeader + 4 /* size */)
+    return false;
+
+  // Have 'MZ' magic for a DOS header?
+  if (start[0] != 'M' || start[1] != 'Z')
+    return false;
+
+  FileOffset file_offset = static_cast<FileOffset>(
+      ReadU32(start, kOffsetOfFileAddressOfNewExeHeader));
+  if (file_offset >= length)
+    return false;
+  const uint8_t* const pe_header = start + file_offset;
+  const size_t kMinPEHeaderSize = 4 /*signature*/ + kSizeOfCoffHeader;
+  if (pe_header <= start || pe_header >= start + length - kMinPEHeaderSize)

[huangs, 2016/06/10 21:10:22]

NIT: I'd prefer
pe_header + kMinPEHeaderSize >= start + length

[etiennep, 2016/06/13 17:50:21]

Done.

+    return false;
+  if (file_offset % 8 != 0)

[huangs, 2016/06/10 21:10:22]

Can combine this condition via || with "file_offset >= length" before.

[etiennep, 2016/06/13 17:50:21]

Done.

+    return false;
+
+  const uint8_t* optional_header = pe_header + 4 + kSizeOfCoffHeader;
+
+  // Check we can read the magic.
+  if (optional_header + 2 >= start + length)
+    return false;
+  if (magic != ReadU16(optional_header, 0))
+    return false;
+
+  return true;
+}
+
 }  // namespace courgette