ring-buffer.c

   1 #include "ring-buffer.h"
   2 #include <stdlib.h>
   3
   4 struct RingBuffer {
   5         int cur;            /* index of current element, last added etc. */
   6         int start;          /* index of first/oldest element */
   7         int end;            /* index of reserved/empty slot */
   8         size_t size;        /* buffer capacity / number of slots */
   9         bool iterating;     /* whether we are in a sequence of prev/next calls */
  10         const void *data[]; /* user supplied buffer content */
  11 };
  12
  13 static int ringbuf_index_prev(RingBuffer *buf, int i) {
  14         return (i-1+buf->size) % buf->size;
  15 }
  16
  17 static int ringbuf_index_next(RingBuffer *buf, int i) {
  18         return (i+1) % buf->size;
  19 }
  20
  21 static bool ringbuf_isfull(RingBuffer *buf) {
  22         return ringbuf_index_next(buf, buf->end) == buf->start;
  23 }
  24
  25 static bool ringbuf_isempty(RingBuffer *buf) {
  26         return buf->start == buf->end;
  27 }
  28
  29 static bool ringbuf_isfirst(RingBuffer *buf) {
  30         return buf->cur == buf->start;
  31 }
  32
  33 static bool ringbuf_islast(RingBuffer *buf) {
  34         return ringbuf_index_next(buf, buf->cur) == buf->end;
  35 }
  36
  37 const void *ringbuf_prev(RingBuffer *buf) {
  38         if (ringbuf_isempty(buf) || (ringbuf_isfirst(buf) && buf->iterating))
  39                 return NULL;
  40         if (buf->iterating)
  41                 buf->cur = ringbuf_index_prev(buf, buf->cur);
  42         buf->iterating = true;
  43         return buf->data[buf->cur];
  44 }
  45
  46 const void *ringbuf_next(RingBuffer *buf) {
  47         if (ringbuf_isempty(buf) || ringbuf_islast(buf))
  48                 return NULL;
  49         buf->cur = ringbuf_index_next(buf, buf->cur);
  50         buf->iterating = true;
  51         return buf->data[buf->cur];
  52 }
  53
  54 void ringbuf_add(RingBuffer *buf, const void *value) {
  55         if (ringbuf_isempty(buf)) {
  56                 buf->end = ringbuf_index_next(buf, buf->end);
  57         } else if (!ringbuf_islast(buf)) {
  58                 buf->cur = ringbuf_index_next(buf, buf->cur);
  59                 buf->end = ringbuf_index_next(buf, buf->cur);
  60         } else if (ringbuf_isfull(buf)) {
  61                 buf->start = ringbuf_index_next(buf, buf->start);
  62                 buf->cur = ringbuf_index_next(buf, buf->cur);
  63                 buf->end = ringbuf_index_next(buf, buf->end);
  64         } else {
  65                 buf->cur = ringbuf_index_next(buf, buf->cur);
  66                 buf->end = ringbuf_index_next(buf, buf->end);
  67         }
  68         buf->data[buf->cur] = value;
  69         buf->iterating = false;
  70 }
  71
  72 void ringbuf_invalidate(RingBuffer *buf) {
  73         buf->iterating = false;
  74 }
  75
  76 RingBuffer *ringbuf_alloc(size_t size) {
  77         RingBuffer *buf;
  78         if ((buf = calloc(1, sizeof(*buf) + (++size)*sizeof(buf->data[0]))))
  79                 buf->size = size;
  80         return buf;
  81 }
  82
  83 void ringbuf_free(RingBuffer *buf) {
  84         free(buf);
  85 }