ringbuffer.c

   1 /*
   2  * Copyright (C) 2006-2009 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 "para.h"
  10 #include "ringbuffer.h"
  11 #include "string.h"
  12
  13 /**
  14  * Holds all information about one ring buffer
  15  *
  16  * It is intentionally not exported via ringbuffer.h. Think abstract.
  17  */
  18 struct ringbuffer
  19 {
  20         /** The size of this ring buffer. */
  21         unsigned size;
  22         /** The actual entries of the ringbuffer. */
  23         void **entries;
  24         /** The next entry will be added at this position. */
  25         int head;
  26         /** How many entries the ring buffer contains. */
  27         unsigned filled;
  28 };
  29
  30 /**
  31  * Initialize a new ringbuffer.
  32  *
  33  * \param size The number of entries the ringbuffer holds.
  34  *
  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'.
  40  *
  41  * \return  A 'cookie' which identifies the ringbuffer just created and
  42  * which must be passed to ringbuffer_add() and ringbuffer_get().
  43  */
  44 struct ringbuffer *ringbuffer_new(unsigned size)
  45 {
  46         struct ringbuffer *rb = para_calloc(sizeof(struct ringbuffer));
  47         rb->entries = para_calloc(size * sizeof(void *));
  48         rb->size = size;
  49         return rb;
  50 };
  51
  52 /**
  53  * Add one entry to a ringbuffer.
  54  *
  55  * \param rb The ringbuffer identifier.
  56  * \param data The data to be inserted.
  57  *
  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
  60  * data.
  61  *
  62  * \return The old \a data pointer which is going to be disregarded, or
  63  * NULL if the ringbuffer is not yet full.
  64  */
  65 void *ringbuffer_add(struct ringbuffer *rb, void *data)
  66 {
  67         void *ret = rb->entries[rb->head];
  68         rb->entries[rb->head] = data;
  69         rb->head = (rb->head + 1) % rb->size;
  70         if (rb->filled < rb->size)
  71                 rb->filled++;
  72         return ret;
  73 }
  74
  75 /**
  76  * Get one entry from a ringbuffer.
  77  *
  78  * \param rb The ringbuffer identifier.
  79  * \param num The number of the entry.
  80  *
  81  * \return A pointer to data previously added, or NULL if entry number
  82  * \a num is not available. \a num counts backwards from zero, i.e.
  83  * ringbuffer_get_entry(0) gets the entry which was added most recently.
  84  */
  85 void *ringbuffer_get(struct ringbuffer *rb, int num)
  86 {
  87         int pos = (rb->head + rb->size - 1 - num) % rb->size;
  88 //      fprintf(stderr, "pos = %d\n", pos);
  89         return rb->entries[pos];
  90 }
  91
  92 /**
  93  * Get the number of entries in the ring buffer.
  94  *
  95  * \param rb The ringbuffer identifier
  96  *
  97  * This function always succeeds and never returns a number greater than the
  98  * size of the ring buffer.
  99  */
 100 unsigned ringbuffer_filled(struct ringbuffer *rb)
 101 {
 102         return rb->filled;
 103 }