win: Add HandleToInt() and IntToHandle()

util/win/handle.h

Index: util/win/handle.h
diff --git a/util/win/handle.h b/util/win/handle.h
new file mode 100644
index 0000000000000000000000000000000000000000..c5a96cae9e7219580e3814881b86787f838244ef
--- /dev/null
+++ b/util/win/handle.h
@@ -0,0 +1,65 @@
+// Copyright 2015 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CRASHPAD_UTIL_WIN_HANDLE_TO_INT_H_
+#define CRASHPAD_UTIL_WIN_HANDLE_TO_INT_H_
+
+#include <windows.h>
+
+namespace crashpad {
+
+//! \brief Converts a `HANDLE` to an `int`.
+//!
+//! `HANDLE` is a `typedef` for `void *`, but `HANDLE` values aren’t necessarily
+//! pointers to anything. Only 32 bits of shareable `HANDLE`s are significant,
+//! even in 64-bit processes on 64-bit operating systems. See <a
+//! href="https://msdn.microsoft.com/en-us/library/windows/desktop/aa384203">Interprocess
+//! Communication Between 32-bit and 64-bit Applications</a>.
+//!
+//! This function safely converts a shareable `HANDLE` to an `int` similarly to
+//! a cast operation. It checks that the operation can be performed safely, and
+//! aborts execution if it cannot.
+//!
+//! \param[in] handle The shareable `HANDLE` to convert.
+//!
+//! \return An equivalent `int`, truncated (if necessary) from \a handle. If
+//!     truncation would have resulted in an `int` that could not be converted
+//!     back to \a handle, aborts execution.
+//!
+//! \sa IntToHandle()
+int HandleToInt(HANDLE handle);
+
+//! \brief Converts an `int` to an `HANDLE`.
+//!
+//! `HANDLE` is a `typedef` for `void *`, but `HANDLE` values aren’t necessarily
+//! pointers to anything. Only 32 bits of shareable `HANDLE`s are significant,
+//! even in 64-bit processes on 64-bit operating systems. See <a
+//! href="https://msdn.microsoft.com/en-us/library/windows/desktop/aa384203">Interprocess
+//! Communication Between 32-bit and 64-bit Applications</a>.
+//!
+//! This function safely convert an `int` to a shareable `HANDLE` similarly to a
+//! cast operation.
+//!
+//! \param[in] handle_int The `int` to convert. This must have been produced by
+//!     HandleToInt(), possibly in a different process.
+//!
+//! \return An equivalent shareable `HANDLE`, sign-extended (if necessary) from
+//!     \a handle_int.
+//!
+//! \sa HandleToInt()
+HANDLE IntToHandle(int handle_int);
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_WIN_HANDLE_TO_INT_H_