include/linux/circ_buf.h

   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  */