ringbuffer.c

   1 /*
   2  * Copyright (C) 2006 Andre Noll <maan@systemlinux.org>
   3  *
   4  *     This program is free software; you can redistribute it and/or modify
   5  *     it under the terms of the GNU General Public License as published by
   6  *     the Free Software Foundation; either version 2 of the License, or
   7  *     (at your option) any later version.
   8  *
   9  *     This program is distributed in the hope that it will be useful,
  10  *     but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  *     GNU General Public License for more details.
  13  *
  14  *     You should have received a copy of the GNU General Public License
  15  *     along with this program; if not, write to the Free Software
  16  *     Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
  17  */
  18
  19 /** \file ringbuffer.c simple ringbuffer implementation */
  20
  21 #include "para.h"
  22 #include "ringbuffer.h"
  23 #include "string.h"
  24
  25 /**
  26  * holds all information about one ring buffer
  27  *
  28  * It is intentionally not exported via ringbuffer.h. Think abstract.
  29  */
  30 struct ringbuffer
  31 {
  32 /**
  33  *
  34  *
  35  * the size of this ring buffer
  36 */
  37 unsigned size;
  38 /**
  39  *
  40  *
  41  * the actual entries of the ringbuffer
  42 */
  43 void **entries;
  44 /**
  45  *
  46  *
  47  * the next entry will be added at this position
  48  */
  49 int head;
  50 /**
  51  *
  52  * how many entries the ring buffer contains
  53 */
  54 unsigned filled;
  55 };
  56
  57 /**
  58  * initialize a new ringbuffer
  59  *
  60  * @param size the number of entries the ringbuffer holds
  61  *
  62  * This function initializes a circular ring buffer which can hold up to \a
  63  * size entries of arbitrary type. If performance is an issue, \a size should
  64  * be a power of two to make the underlying modulo operations cheap. Arbitrary
  65  * many ringbuffers may be initialized via this function. Each ringbuffer is
  66  * identified by a 'cookie'.
  67  *
  68  * Return value: A 'cookie' which identifies the ringbuffer just created and
  69  * which must be passed to ringbuffer_add() and ringbuffer_get().
  70  */
  71 void *ringbuffer_new(unsigned size)
  72 {
  73         struct ringbuffer *rb = para_calloc(sizeof(struct ringbuffer));
  74         rb->entries = para_calloc(size * sizeof(void *));
  75         rb->size = size;
  76         return rb;
  77 };
  78
  79 /**
  80  * add one entry to a ringbuffer
  81  *
  82  * @param cookie the ringbuffer identifier
  83  * @param data the data to be inserted
  84  *
  85  * insert \a data into the ringbuffer associated with \a cookie.  As soon as
  86  * the ringbuffer fills up, its oldest entry is disregarded and replaced by \a
  87  * data.
  88  *
  89  * \return The old \a data pointer which is going to be disregarded, or
  90  * NULL if the ringbuffer is not yet full.
  91  */
  92 void *ringbuffer_add(void *cookie, void *data)
  93 {
  94         struct ringbuffer *rb = cookie;
  95         void *ret = rb->entries[rb->head];
  96         rb->entries[rb->head] = data;
  97         rb->head = (rb->head + 1) % rb->size;
  98         if (rb->filled < rb->size)
  99                 rb->filled++;
 100         return ret;
 101 }
 102
 103 /**
 104  * get one entry from a ringbuffer
 105  *
 106  * @param cookie the ringbuffer identifier
 107  * @param num the number of the entry
 108  *
 109  * \return A pointer to data previously added, or NULL if entry number
 110  * \a num is not available. \a num counts backwards from zero, i.e.
 111  * ringbuffer_get_entry(0) gets the entry which was added most recently.
 112  */
 113 void *ringbuffer_get(void *cookie, int num)
 114 {
 115         struct ringbuffer *rb = cookie;
 116         int pos = (rb->head + rb->size - 1 - num) % rb->size;
 117 //      fprintf(stderr, "pos = %d\n", pos);
 118         return rb->entries[pos];
 119 }
 120
 121 /**
 122  * get the number of entries in the ring buffer
 123  *
 124  * @param cookie the ringbuffer identifier
 125  *
 126  * This function always succeeds and never returns a number greater than the
 127  * size of the ring buffer.
 128  */
 129 unsigned ringbuffer_filled(void *cookie)
 130 {
 131         struct ringbuffer *rb = cookie;
 132         return rb->filled;
 133 }