util/Cast: new utility library

1 files changed, 58 insertions, 0 deletions

diff --git a/src/util/Cast.hxx b/src/util/Cast.hxx
new file mode 100644
index 000000000..69172e6de
--- /dev/null
+++ b/src/util/Cast.hxx
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2013 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef CAST_HXX
+#define CAST_HXX
+
+#include <stddef.h>
+
+/**
+ * Offset the given pointer by the specified number of bytes.
+ */
+static constexpr void *
+OffsetPointer(void *p, ptrdiff_t offset)
+{
+    return (char *)p + offset;
+}
+
+template<typename T, typename U>
+static constexpr T *
+OffsetCast(U *p, ptrdiff_t offset)
+{
+    return reinterpret_cast<T *>(OffsetPointer(p, offset));
+}
+
+/**
+ * Cast the given pointer to a struct member to its parent structure.
+ */
+#define ContainerCast(p, container, attribute) \
+    OffsetCast<container, decltype(((container*)nullptr)->attribute)>\
+    ((p), -ptrdiff_t(offsetof(container, attribute)))
+
+#endif