1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * See Documentation/core-api/circular-buffers.rst for more information.
4 */
5
6#ifndef _LINUX_CIRC_BUF_H
7#define _LINUX_CIRC_BUF_H 1
8
9struct circ_buf {
10	char *buf;
11	int head;
12	int tail;
13};
14
15/* Return count in buffer.  */
16#define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))
17
18/* Return space available, 0..size-1.  We always leave one free char
19   as a completely full buffer has head == tail, which is the same as
20   empty.  */
21#define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))
22
23/* Return count up to the end of the buffer.  Carefully avoid
24   accessing head and tail more than once, so they can change
25   underneath us without returning inconsistent results.  */
26#define CIRC_CNT_TO_END(head,tail,size) \
27	({int end = (size) - (tail); \
28	  int n = ((head) + end) & ((size)-1); \
29	  n < end ? n : end;})
30
31/* Return space available up to the end of the buffer.  */
32#define CIRC_SPACE_TO_END(head,tail,size) \
33	({int end = (size) - 1 - (head); \
34	  int n = (end + (tail)) & ((size)-1); \
35	  n <= end ? n : end+1;})
36
37#endif /* _LINUX_CIRC_BUF_H  */
38