ringbuffer.c

   1 /*
   2  * Copyright (C) 2006-2011 Andre Noll <maan@systemlinux.org>
   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 }