1/*
2 * See Documentation/circular-buffers.txt for more information.
3 */
4
5#ifndef _LINUX_CIRC_BUF_H
6#define _LINUX_CIRC_BUF_H 1
7
8struct circ_buf {
9	char *buf;
10	int head;
11	int tail;
12};
13
14/* Return count in buffer.  */
15#define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))
16
17/* Return space available, 0..size-1.  We always leave one free char
18   as a completely full buffer has head == tail, which is the same as
19   empty.  */
20#define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))
21
22/* Return count up to the end of the buffer.  Carefully avoid
23   accessing head and tail more than once, so they can change
24   underneath us without returning inconsistent results.  */
25#define CIRC_CNT_TO_END(head,tail,size) \
26	({int end = (size) - (tail); \
27	  int n = ((head) + end) & ((size)-1); \
28	  n < end ? n : end;})
29
30/* Return space available up to the end of the buffer.  */
31#define CIRC_SPACE_TO_END(head,tail,size) \
32	({int end = (size) - 1 - (head); \
33	  int n = (end + (tail)) & ((size)-1); \
34	  n <= end ? n : end+1;})
35
36#endif /* _LINUX_CIRC_BUF_H  */
37