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+#ifndef INCLUDED_RINGBUF_H
+#define INCLUDED_RINGBUF_H
+
+/*
+ * ringbuf.h - C ring buffer (FIFO) interface.
+ *
+ * Written in 2011 by Drew Hess <dhess-src@bothan.net>.
+ *
+ * To the extent possible under law, the author(s) have dedicated all
+ * copyright and related and neighboring rights to this software to
+ * the public domain worldwide. This software is distributed without
+ * any warranty.
+ *
+ * You should have received a copy of the CC0 Public Domain Dedication
+ * along with this software. If not, see
+ * <http://creativecommons.org/publicdomain/zero/1.0/>.
+ */
+
+/*
+ * A byte-addressable ring buffer FIFO implementation.
+ *
+ * The ring buffer's head pointer points to the starting location
+ * where data should be written when copying data *into* the buffer
+ * (e.g., with ringbuf_read). The ring buffer's tail pointer points to
+ * the starting location where data should be read when copying data
+ * *from* the buffer (e.g., with ringbuf_write).
+ */
+
+#include <stddef.h>
+#include <sys/types.h>
+
+typedef struct ringbuf_t *ringbuf_t;
+
+/*
+ * Create a new ring buffer with the given capacity (usable
+ * bytes). Note that the actual internal buffer size may be one or
+ * more bytes larger than the usable capacity, for bookkeeping.
+ *
+ * Returns the new ring buffer object, or 0 if there's not enough
+ * memory to fulfill the request for the given capacity.
+ */
+ringbuf_t
+ringbuf_new(size_t capacity);
+
+/*
+ * The size of the internal buffer, in bytes. One or more bytes may be
+ * unusable in order to distinguish the "buffer full" state from the
+ * "buffer empty" state.
+ *
+ * For the usable capacity of the ring buffer, use the
+ * ringbuf_capacity function.
+ */
+size_t
+ringbuf_buffer_size(const struct ringbuf_t *rb);
+
+/*
+ * Deallocate a ring buffer, and, as a side effect, set the pointer to
+ * 0.
+ */
+void
+ringbuf_free(ringbuf_t *rb);
+
+/*
+ * Reset a ring buffer to its initial state (empty).
+ */
+void
+ringbuf_reset(ringbuf_t rb);
+
+/*
+ * The usable capacity of the ring buffer, in bytes. Note that this
+ * value may be less than the ring buffer's internal buffer size, as
+ * returned by ringbuf_buffer_size.
+ */
+size_t
+ringbuf_capacity(const struct ringbuf_t *rb);
+
+/*
+ * The number of free/available bytes in the ring buffer. This value
+ * is never larger than the ring buffer's usable capacity.
+ */
+size_t
+ringbuf_bytes_free(const struct ringbuf_t *rb);
+
+/*
+ * The number of bytes currently being used in the ring buffer. This
+ * value is never larger than the ring buffer's usable capacity.
+ */
+size_t
+ringbuf_bytes_used(const struct ringbuf_t *rb);
+
+int
+ringbuf_is_full(const struct ringbuf_t *rb);
+
+int
+ringbuf_is_empty(const struct ringbuf_t *rb);
+
+/*
+ * Const access to the head and tail pointers of the ring buffer.
+ */
+const void *
+ringbuf_tail(const struct ringbuf_t *rb);
+
+const void *
+ringbuf_head(const struct ringbuf_t *rb);
+
+/*
+ * Locate the first occurrence of character c (converted to an
+ * unsigned char) in ring buffer rb, beginning the search at offset
+ * bytes from the ring buffer's tail pointer. The function returns the
+ * offset of the character from the ring buffer's tail pointer, if
+ * found. If c does not occur in the ring buffer, the function returns
+ * the number of bytes used in the ring buffer.
+ *
+ * Note that the offset parameter and the returned offset are logical
+ * offsets from the tail pointer, not necessarily linear offsets.
+ */
+size_t
+ringbuf_findchr(const struct ringbuf_t *rb, int c, size_t offset);
+
+/*
+ * Beginning at ring buffer dst's head pointer, fill the ring buffer
+ * with a repeating sequence of len bytes, each of value c (converted
+ * to an unsigned char). len can be as large as you like, but the
+ * function will never write more than ringbuf_buffer_size(dst) bytes
+ * in a single invocation, since that size will cause all bytes in the
+ * ring buffer to be written exactly once each.
+ *
+ * Note that if len is greater than the number of free bytes in dst,
+ * the ring buffer will overflow. When an overflow occurs, the state
+ * of the ring buffer is guaranteed to be consistent, including the
+ * head and tail pointers; old data will simply be overwritten in FIFO
+ * fashion, as needed. However, note that, if calling the function
+ * results in an overflow, the value of the ring buffer's tail pointer
+ * may be different than it was before the function was called.
+ *
+ * Returns the actual number of bytes written to dst: len, if
+ * len < ringbuf_buffer_size(dst), else ringbuf_buffer_size(dst).
+ */
+size_t
+ringbuf_memset(ringbuf_t dst, int c, size_t len);
+
+/*
+ * Copy n bytes from a contiguous memory area src into the ring buffer
+ * dst. Returns the ring buffer's new head pointer.
+ *
+ * It is possible to copy more data from src than is available in the
+ * buffer; i.e., it's possible to overflow the ring buffer using this
+ * function. When an overflow occurs, the state of the ring buffer is
+ * guaranteed to be consistent, including the head and tail pointers;
+ * old data will simply be overwritten in FIFO fashion, as
+ * needed. However, note that, if calling the function results in an
+ * overflow, the value of the ring buffer's tail pointer may be
+ * different than it was before the function was called.
+ */
+void *
+ringbuf_memcpy_into(ringbuf_t dst, const void *src, size_t count);
+
+/*
+ * This convenience function calls read(2) on the file descriptor fd,
+ * using the ring buffer rb as the destination buffer for the read,
+ * and returns the value returned by read(2). It will only call
+ * read(2) once, and may return a short count.
+ *
+ * It is possible to read more data from the file descriptor than is
+ * available in the buffer; i.e., it's possible to overflow the ring
+ * buffer using this function. When an overflow occurs, the state of
+ * the ring buffer is guaranteed to be consistent, including the head
+ * and tail pointers: old data will simply be overwritten in FIFO
+ * fashion, as needed. However, note that, if calling the function
+ * results in an overflow, the value of the ring buffer's tail pointer
+ * may be different than it was before the function was called.
+ */
+ssize_t
+ringbuf_read(int fd, ringbuf_t rb, size_t count);
+
+/*
+ * Copy n bytes from the ring buffer src, starting from its tail
+ * pointer, into a contiguous memory area dst. Returns the value of
+ * src's tail pointer after the copy is finished.
+ *
+ * Note that this copy is destructive with respect to the ring buffer:
+ * the n bytes copied from the ring buffer are no longer available in
+ * the ring buffer after the copy is complete, and the ring buffer
+ * will have n more free bytes than it did before the function was
+ * called.
+ *
+ * This function will *not* allow the ring buffer to underflow. If
+ * count is greater than the number of bytes used in the ring buffer,
+ * no bytes are copied, and the function will return 0.
+ */
+void *
+ringbuf_memcpy_from(void *dst, ringbuf_t src, size_t count);
+
+/*
+ * This convenience function calls write(2) on the file descriptor fd,
+ * using the ring buffer rb as the source buffer for writing (starting
+ * at the ring buffer's tail pointer), and returns the value returned
+ * by write(2). It will only call write(2) once, and may return a
+ * short count.
+ *
+ * Note that this copy is destructive with respect to the ring buffer:
+ * any bytes written from the ring buffer to the file descriptor are
+ * no longer available in the ring buffer after the copy is complete,
+ * and the ring buffer will have N more free bytes than it did before
+ * the function was called, where N is the value returned by the
+ * function (unless N is < 0, in which case an error occurred and no
+ * bytes were written).
+ *
+ * This function will *not* allow the ring buffer to underflow. If
+ * count is greater than the number of bytes used in the ring buffer,
+ * no bytes are written to the file descriptor, and the function will
+ * return 0.
+ */
+ssize_t
+ringbuf_write(int fd, ringbuf_t rb, size_t count);
+
+/*
+ * Copy count bytes from ring buffer src, starting from its tail
+ * pointer, into ring buffer dst. Returns dst's new head pointer after
+ * the copy is finished.
+ *
+ * Note that this copy is destructive with respect to the ring buffer
+ * src: any bytes copied from src into dst are no longer available in
+ * src after the copy is complete, and src will have 'count' more free
+ * bytes than it did before the function was called.
+ *
+ * It is possible to copy more data from src than is available in dst;
+ * i.e., it's possible to overflow dst using this function. When an
+ * overflow occurs, the state of dst is guaranteed to be consistent,
+ * including the head and tail pointers; old data will simply be
+ * overwritten in FIFO fashion, as needed. However, note that, if
+ * calling the function results in an overflow, the value dst's tail
+ * pointer may be different than it was before the function was
+ * called.
+ *
+ * It is *not* possible to underflow src; if count is greater than the
+ * number of bytes used in src, no bytes are copied, and the function
+ * returns 0.
+ */
+void *
+ringbuf_copy(ringbuf_t dst, ringbuf_t src, size_t count);
+
+#endif /* INCLUDED_RINGBUF_H */