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#ifndef _LINUX_CIRC_BUF_H
#define _LINUX_CIRC_BUF_H 1
struct circ_buf {
char *buf;
int head;
int tail;
};
/* Return count in buffer. */
#define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))
/* Return space available, 0..size-1. We always leave one free char
as a completely full buffer has head == tail, which is the same as
empty. */
#define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))
/* Return count up to the end of the buffer. Carefully avoid
accessing head and tail more than once, so they can change
underneath us without returning inconsistent results. */
#define CIRC_CNT_TO_END(head,tail,size) \
({int end = (size) - (tail); \
int n = ((head) + end) & ((size)-1); \
n < end ? n : end;})
/* Return space available up to the end of the buffer. */
#define CIRC_SPACE_TO_END(head,tail,size) \
({int end = (size) - 1 - (head); \
int n = (end + (tail)) & ((size)-1); \
n <= end ? n : end+1;})
#endif /* _LINUX_CIRC_BUF_H */