LXR linux/include/linux/circ

   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