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+//
+//  TPCircularBuffer.h
+//  Circular/Ring buffer implementation
+//
+//  https://github.com/michaeltyson/TPCircularBuffer
+//
+//  Created by Michael Tyson on 10/12/2011.
+//
+//
+//  This implementation makes use of a virtual memory mapping technique that inserts a virtual copy
+//  of the buffer memory directly after the buffer's end, negating the need for any buffer
+//  wrap-around logic. Clients can simply use the returned memory address as if it were contiguous
+//  space.
+//
+//  The implementation is thread-safe in the case of a single producer and single consumer.
+//
+//  Virtual memory technique originally proposed by Philip Howard (http://vrb.slashusr.org/), and
+//  adapted to Darwin by Kurt Revis (http://www.snoize.com,
+//  http://www.snoize.com/Code/PlayBufferedSoundFile.tar.gz)
+//
+//
+//  Copyright (C) 2012-2013 A Tasty Pixel
+//
+//  This software is provided 'as-is', without any express or implied
+//  warranty.  In no event will the authors be held liable for any damages
+//  arising from the use of this software.
+//
+//  Permission is granted to anyone to use this software for any purpose,
+//  including commercial applications, and to alter it and redistribute it
+//  freely, subject to the following restrictions:
+//
+//  1. The origin of this software must not be misrepresented; you must not
+//     claim that you wrote the original software. If you use this software
+//     in a product, an acknowledgment in the product documentation would be
+//     appreciated but is not required.
+//
+//  2. Altered source versions must be plainly marked as such, and must not be
+//     misrepresented as being the original software.
+//
+//  3. This notice may not be removed or altered from any source distribution.
+//
+
+#ifndef TPCircularBuffer_h
+#define TPCircularBuffer_h
+
+#include <libkern/OSAtomic.h>
+#include <string.h>
+#include <winpr/assert.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+	typedef struct
+	{
+		void* buffer;
+		int32_t length;
+		int32_t tail;
+		int32_t head;
+		volatile int32_t fillCount;
+	} TPCircularBuffer;
+
+	/*!
+	 * Initialise buffer
+	 *
+	 *  Note that the length is advisory only: Because of the way the
+	 *  memory mirroring technique works, the true buffer length will
+	 *  be multiples of the device page size (e.g. 4096 bytes)
+	 *
+	 * @param buffer Circular buffer
+	 * @param length Length of buffer
+	 */
+	bool TPCircularBufferInit(TPCircularBuffer* buffer, int32_t length);
+
+	/*!
+	 * Cleanup buffer
+	 *
+	 *  Releases buffer resources.
+	 */
+	void TPCircularBufferCleanup(TPCircularBuffer* buffer);
+
+	/*!
+	 * Clear buffer
+	 *
+	 *  Resets buffer to original, empty state.
+	 *
+	 *  This is safe for use by consumer while producer is accessing
+	 *  buffer.
+	 */
+	void TPCircularBufferClear(TPCircularBuffer* buffer);
+
+	// Reading (consuming)
+
+	/*!
+	 * Access end of buffer
+	 *
+	 *  This gives you a pointer to the end of the buffer, ready
+	 *  for reading, and the number of available bytes to read.
+	 *
+	 * @param buffer Circular buffer
+	 * @param availableBytes On output, the number of bytes ready for reading
+	 * @return Pointer to the first bytes ready for reading, or NULL if buffer is empty
+	 */
+	static __inline__ __attribute__((always_inline)) void*
+	TPCircularBufferTail(TPCircularBuffer* buffer, int32_t* availableBytes)
+	{
+		*availableBytes = buffer->fillCount;
+		if (*availableBytes == 0)
+			return NULL;
+		return (void*)((char*)buffer->buffer + buffer->tail);
+	}
+
+	/*!
+	 * Consume bytes in buffer
+	 *
+	 *  This frees up the just-read bytes, ready for writing again.
+	 *
+	 * @param buffer Circular buffer
+	 * @param amount Number of bytes to consume
+	 */
+	static __inline__ __attribute__((always_inline)) void
+	TPCircularBufferConsume(TPCircularBuffer* buffer, int32_t amount)
+	{
+		buffer->tail = (buffer->tail + amount) % buffer->length;
+		OSAtomicAdd32Barrier(-amount, &buffer->fillCount);
+		WINPR_ASSERT(buffer->fillCount >= 0);
+	}
+
+	/*!
+	 * Version of TPCircularBufferConsume without the memory barrier, for more optimal use in
+	 * single-threaded contexts
+	 */
+	static __inline__ __attribute__((always_inline)) void
+	TPCircularBufferConsumeNoBarrier(TPCircularBuffer* buffer, int32_t amount)
+	{
+		buffer->tail = (buffer->tail + amount) % buffer->length;
+		buffer->fillCount -= amount;
+		WINPR_ASSERT(buffer->fillCount >= 0);
+	}
+
+	/*!
+	 * Access front of buffer
+	 *
+	 *  This gives you a pointer to the front of the buffer, ready
+	 *  for writing, and the number of available bytes to write.
+	 *
+	 * @param buffer Circular buffer
+	 * @param availableBytes On output, the number of bytes ready for writing
+	 * @return Pointer to the first bytes ready for writing, or NULL if buffer is full
+	 */
+	static __inline__ __attribute__((always_inline)) void*
+	TPCircularBufferHead(TPCircularBuffer* buffer, int32_t* availableBytes)
+	{
+		*availableBytes = (buffer->length - buffer->fillCount);
+		if (*availableBytes == 0)
+			return NULL;
+		return (void*)((char*)buffer->buffer + buffer->head);
+	}
+
+	// Writing (producing)
+
+	/*!
+	 * Produce bytes in buffer
+	 *
+	 *  This marks the given section of the buffer ready for reading.
+	 *
+	 * @param buffer Circular buffer
+	 * @param amount Number of bytes to produce
+	 */
+	static __inline__ __attribute__((always_inline)) void
+	TPCircularBufferProduce(TPCircularBuffer* buffer, int amount)
+	{
+		buffer->head = (buffer->head + amount) % buffer->length;
+		OSAtomicAdd32Barrier(amount, &buffer->fillCount);
+		WINPR_ASSERT(buffer->fillCount <= buffer->length);
+	}
+
+	/*!
+	 * Version of TPCircularBufferProduce without the memory barrier, for more optimal use in
+	 * single-threaded contexts
+	 */
+	static __inline__ __attribute__((always_inline)) void
+	TPCircularBufferProduceNoBarrier(TPCircularBuffer* buffer, int amount)
+	{
+		buffer->head = (buffer->head + amount) % buffer->length;
+		buffer->fillCount += amount;
+		WINPR_ASSERT(buffer->fillCount <= buffer->length);
+	}
+
+	/*!
+	 * Helper routine to copy bytes to buffer
+	 *
+	 *  This copies the given bytes to the buffer, and marks them ready for writing.
+	 *
+	 * @param buffer Circular buffer
+	 * @param src Source buffer
+	 * @param len Number of bytes in source buffer
+	 * @return true if bytes copied, false if there was insufficient space
+	 */
+	static __inline__ __attribute__((always_inline)) bool
+	TPCircularBufferProduceBytes(TPCircularBuffer* buffer, const void* src, int32_t len)
+	{
+		int32_t space;
+		void* ptr = TPCircularBufferHead(buffer, &space);
+		if (space < len)
+			return false;
+		memcpy(ptr, src, len);
+		TPCircularBufferProduce(buffer, len);
+		return true;
+	}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif