ringbuffer.c

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