util/ConstBuffer: new utility class

Makefile.am

@@ -259,6 +259,7 @@ libutil_a_SOURCES = \
 	src/util/RefCount.hxx \
 	src/util/fifo_buffer.c src/util/fifo_buffer.h \
 	src/util/FifoBuffer.hxx \
+	src/util/ConstBuffer.hxx \
 	src/util/WritableBuffer.hxx \
 	src/util/growing_fifo.c src/util/growing_fifo.h \
 	src/util/LazyRandomEngine.cxx src/util/LazyRandomEngine.hxx \

src/util/ConstBuffer.hxx

+/*
+ * 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 CONST_BUFFER_HPP
+#define CONST_BUFFER_HPP
+
+#include "Compiler.h"
+
+#include <cstddef>
+
+#ifndef NDEBUG
+#include <assert.h>
+#endif
+
+/**
+ * A reference to a memory area that is read-only.
+ */
+template<typename T>
+struct ConstBuffer {
+	typedef size_t size_type;
+	typedef const T *pointer_type;
+	typedef pointer_type const_pointer_type;
+	typedef pointer_type iterator;
+	typedef pointer_type const_iterator;
+
+	pointer_type data;
+	size_type size;
+
+	ConstBuffer() = default;
+
+	constexpr ConstBuffer(std::nullptr_t):data(nullptr), size(0) {}
+
+	constexpr ConstBuffer(pointer_type _data, size_type _size)
+		:data(_data), size(_size) {}
+
+	constexpr static ConstBuffer Null() {
+		return ConstBuffer(nullptr, 0);
+	}
+
+	/**
+	 * Cast a ConstBuffer<void> to a ConstBuffer<T>.  A "void"
+	 * buffer records its size in bytes, and when casting to "T",
+	 * the assertion below ensures that the size is a multiple of
+	 * sizeof(T).
+	 */
+#ifdef NDEBUG
+	constexpr
+#endif
+	static ConstBuffer<T> FromVoid(ConstBuffer<void> other) {
+		static_assert(sizeof(T) > 0, "Empty base type");
+#ifndef NDEBUG
+		assert(other.size % sizeof(T) == 0);
+#endif
+		return ConstBuffer<T>(pointer_type(other.data),
+				      other.size / sizeof(T));
+	}
+
+	constexpr ConstBuffer<void> ToVoid() const {
+		static_assert(sizeof(T) > 0, "Empty base type");
+		return ConstBuffer<void>(data, size * sizeof(T));
+	}
+
+	constexpr bool IsNull() const {
+		return data == nullptr;
+	}
+
+	constexpr bool IsEmpty() const {
+		return size == 0;
+	}
+
+	constexpr iterator begin() const {
+		return data;
+	}
+
+	constexpr iterator end() const {
+		return data + size;
+	}
+
+	constexpr const_iterator cbegin() const {
+		return data;
+	}
+
+	constexpr const_iterator cend() const {
+		return data + size;
+	}
+
+	constexpr operator ConstBuffer<void>() const {
+		return { data, size };
+	}
+};
+
+#endif