linux/include/linux/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
   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  */
  37
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