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David Howells90fddab2010-03-24 09:43:00 +00001/*
2 * See Documentation/circular-buffers.txt for more information.
3 */
4
Linus Torvalds1da177e2005-04-16 15:20:36 -07005#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 */