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