2 * Copyright (C) 2006-2007 Andre Noll <maan@systemlinux.org>
4 * Licensed under the GPL v2. For licencing details see COPYING.
7 /** \file ringbuffer.c Simple ringbuffer implementation */
10 #include "ringbuffer.h"
14 * Holds all information about one ring buffer
16 * It is intentionally not exported via ringbuffer.h. Think abstract.
20 /** The size of this ring buffer. */
22 /** The actual entries of the ringbuffer. */
24 /** The next entry will be added at this position. */
26 /** How many entries the ring buffer contains. */
31 * Initialize a new ringbuffer.
33 * \param size The number of entries the ringbuffer holds.
35 * This function initializes a circular ring buffer which can hold up to \a
36 * size entries of arbitrary type. If performance is an issue, \a size should
37 * be a power of two to make the underlying modulo operations cheap. Arbitrary
38 * many ringbuffers may be initialized via this function. Each ringbuffer is
39 * identified by a 'cookie'.
41 * \return A 'cookie' which identifies the ringbuffer just created and
42 * which must be passed to ringbuffer_add() and ringbuffer_get().
44 void *ringbuffer_new(unsigned size)
46 struct ringbuffer *rb = para_calloc(sizeof(struct ringbuffer));
47 rb->entries = para_calloc(size * sizeof(void *));
53 * Add one entry to a ringbuffer.
55 * \param cookie The ringbuffer identifier.
56 * \param data The data to be inserted.
58 * Insert \a data into the ringbuffer associated with \a cookie. As soon as
59 * the ringbuffer fills up, its oldest entry is disregarded and replaced by \a
62 * \return The old \a data pointer which is going to be disregarded, or
63 * NULL if the ringbuffer is not yet full.
65 void *ringbuffer_add(void *cookie, void *data)
67 struct ringbuffer *rb = cookie;
68 void *ret = rb->entries[rb->head];
69 rb->entries[rb->head] = data;
70 rb->head = (rb->head + 1) % rb->size;
71 if (rb->filled < rb->size)
77 * Get one entry from a ringbuffer.
79 * \param cookie The ringbuffer identifier.
80 * \param num The number of the entry.
82 * \return A pointer to data previously added, or NULL if entry number
83 * \a num is not available. \a num counts backwards from zero, i.e.
84 * ringbuffer_get_entry(0) gets the entry which was added most recently.
86 void *ringbuffer_get(void *cookie, int num)
88 struct ringbuffer *rb = cookie;
89 int pos = (rb->head + rb->size - 1 - num) % rb->size;
90 // fprintf(stderr, "pos = %d\n", pos);
91 return rb->entries[pos];
95 * Get the number of entries in the ring buffer.
97 * \param cookie The ringbuffer identifier
99 * This function always succeeds and never returns a number greater than the
100 * size of the ring buffer.
102 unsigned ringbuffer_filled(void *cookie)
104 struct ringbuffer *rb = cookie;