LXR linux/include/linux/circ

   1/* SPDX-License-Identifier: GPL-2.0 */
   2/*
   3 * See Documentation/core-api/circular-buffers.rst for more information.
   4 */
   5
   6#ifndef _LINUX_CIRC_BUF_H
   7#define _LINUX_CIRC_BUF_H 1
   8
   9struct circ_buf {
  10        char *buf;
  11        int head;
  12        int tail;
  13};
  14
  15/* Return count in buffer.  */
  16#define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))
  17
  18/* Return space available, 0..size-1.  We always leave one free char
  19   as a completely full buffer has head == tail, which is the same as
  20   empty.  */
  21#define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))
  22
  23/* Return count up to the end of the buffer.  Carefully avoid
  24   accessing head and tail more than once, so they can change
  25   underneath us without returning inconsistent results.  */
  26#define CIRC_CNT_TO_END(head,tail,size) \
  27        ({int end = (size) - (tail); \
  28          int n = ((head) + end) & ((size)-1); \
  29          n < end ? n : end;})
  30
  31/* Return space available up to the end of the buffer.  */
  32#define CIRC_SPACE_TO_END(head,tail,size) \
  33        ({int end = (size) - 1 - (head); \
  34          int n = (end + (tail)) & ((size)-1); \
  35          n <= end ? n : end+1;})
  36
  37#endif /* _LINUX_CIRC_BUF_H  */
  38