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circ_buf.h
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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 
8 struct 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 */