PcmBuffer: move code to new class ReusableBuffer

ReusableBuffer is more generic.

src/util/ReusableArray.hxx

@@ -0,0 +1,88 @@
+/*
+ * 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 REUSABLE_ARRAY_HXX
+#define REUSABLE_ARRAY_HXX
+
+#include <stddef.h>
+
+#include "gcc.h"
+
+/**
+ * Manager for a temporary array which grows as needed.  This attempts
+ * to reduce the number of consecutive heap allocations and
+ * deallocations.
+ *
+ * @param T the array element type
+ * @param M always allocate multiples of this number; must be a power of 2
+ */
+template<typename T, size_t M=1>
+class ReusableArray {
+	T *buffer;
+	size_t capacity;
+
+public:
+	ReusableArray():buffer(nullptr), capacity(0) {}
+
+	ReusableArray(const ReusableArray &other) = delete;
+	ReusableArray &operator=(const ReusableArray &other) = delete;
+
+	~ReusableArray() {
+		delete[] buffer;
+	}
+
+	/**
+	 * Free resources allocated by this object.  This invalidates
+	 * the buffer returned by Get().
+	 */
+	void Clear() {
+		delete[] buffer;
+		buffer = nullptr;
+		capacity = 0;
+	}
+
+	/**
+	 * Get the buffer, and guarantee a minimum size.  This buffer
+	 * becomes invalid with the next Get() call.
+	 */
+	gcc_malloc
+	T *Get(size_t size) {
+		if (gcc_unlikely(size > capacity)) {
+			/* too small: grow */
+			delete[] buffer;
+
+			capacity = ((size - 1) | (M - 1)) + 1;
+			buffer = new T[capacity];
+		}
+
+		return buffer;
+	}
+};
+
+#endif