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
9 struct 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 */