crypt.c: Combine load_key() and get_private_key().
[paraslash.git] / ringbuffer.c
1 /*
2 * Copyright (C) 2006 Andre Noll <maan@tuebingen.mpg.de>
3 *
4 * Licensed under the GPL v2. For licencing details see COPYING.
5 */
6
7 /** \file ringbuffer.c Simple ringbuffer implementation */
8
9 #include <regex.h>
10
11 #include "para.h"
12 #include "ringbuffer.h"
13 #include "string.h"
14
15 /**
16 * Holds all information about one ring buffer
17 *
18 * It is intentionally not exported via ringbuffer.h. Think abstract.
19 */
20 struct ringbuffer
21 {
22 /** The size of this ring buffer. */
23 unsigned size;
24 /** The actual entries of the ringbuffer. */
25 void **entries;
26 /** The next entry will be added at this position. */
27 int head;
28 /** How many entries the ring buffer contains. */
29 unsigned filled;
30 };
31
32 /**
33 * Initialize a new ringbuffer.
34 *
35 * \param size The number of entries the ringbuffer holds.
36 *
37 * This function initializes a circular ring buffer which can hold up to \a
38 * size entries of arbitrary type. If performance is an issue, \a size should
39 * be a power of two to make the underlying modulo operations cheap. Arbitrary
40 * many ringbuffers may be initialized via this function. Each ringbuffer is
41 * identified by a 'cookie'.
42 *
43 * \return A 'cookie' which identifies the ringbuffer just created and
44 * which must be passed to ringbuffer_add() and ringbuffer_get().
45 */
46 struct ringbuffer *ringbuffer_new(unsigned size)
47 {
48 struct ringbuffer *rb = para_calloc(sizeof(struct ringbuffer));
49 rb->entries = para_calloc(size * sizeof(void *));
50 rb->size = size;
51 return rb;
52 }
53
54 /**
55 * Add one entry to a ringbuffer.
56 *
57 * \param rb The ringbuffer identifier.
58 * \param data The data to be inserted.
59 *
60 * Insert \a data into the ringbuffer associated with \a cookie. As soon as
61 * the ringbuffer fills up, its oldest entry is disregarded and replaced by \a
62 * data.
63 *
64 * \return The old \a data pointer which is going to be disregarded, or
65 * NULL if the ringbuffer is not yet full.
66 */
67 void *ringbuffer_add(struct ringbuffer *rb, void *data)
68 {
69 void *ret = rb->entries[rb->head];
70 rb->entries[rb->head] = data;
71 rb->head = (rb->head + 1) % rb->size;
72 if (rb->filled < rb->size)
73 rb->filled++;
74 return ret;
75 }
76
77 /**
78 * Get one entry from a ringbuffer.
79 *
80 * \param rb The ringbuffer identifier.
81 * \param num The number of the entry.
82 *
83 * \return A pointer to data previously added, or NULL if entry number
84 * \a num is not available. \a num counts backwards from zero, i.e.
85 * ringbuffer_get_entry(0) gets the entry which was added most recently.
86 */
87 void *ringbuffer_get(struct ringbuffer *rb, int num)
88 {
89 int pos = (rb->head + rb->size - 1 - num) % rb->size;
90 // fprintf(stderr, "pos = %d\n", pos);
91 return rb->entries[pos];
92 }
93
94 /**
95 * Get the number of entries in the ring buffer.
96 *
97 * \param rb The ringbuffer identifier
98 *
99 * \return This function always succeeds. It returns a number less than the
100 * size of the ring buffer.
101 */
102 unsigned ringbuffer_filled(struct ringbuffer *rb)
103 {
104 return rb->filled;
105 }