include/linux/circ_buf.h

   1 #ifndef _LINUX_CIRC_BUF_H
   2 #define _LINUX_CIRC_BUF_H 1
   3
   4 struct 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  */