sys/dev/drm/include/linux/circ_buf.h

   1 /*
   2  * Copyright (c) 2016 Rimvydas Jasinskas
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice unmodified, this list of conditions, and the following
  10  *    disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #ifndef _LINUX_CIRC_BUF_H
  28 #define _LINUX_CIRC_BUF_H
  29
  30 struct circ_buf {
  31         char *buf;
  32         int head;
  33         int tail;
  34 };
  35
  36 /* Return count in buffer.  */
  37 #define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))
  38
  39 /* Return space available, 0..size-1.  We always leave one free char
  40    as a completely full buffer has head == tail, which is the same as
  41    empty.  */
  42 #define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))
  43
  44 /* Return count up to the end of the buffer.  Carefully avoid
  45    accessing head and tail more than once, so they can change
  46    underneath us without returning inconsistent results.  */
  47 #define CIRC_CNT_TO_END(head,tail,size) \
  48         ({int end = (size) - (tail); \
  49           int n = ((head) + end) & ((size)-1); \
  50           n < end ? n : end;})
  51
  52 /* Return space available up to the end of the buffer.  */
  53 #define CIRC_SPACE_TO_END(head,tail,size) \
  54         ({int end = (size) - 1 - (head); \
  55           int n = (end + (tail)) & ((size)-1); \
  56           n <= end ? n : end+1;})
  57
  58 #endif  /* _LINUX_CIRC_BUF_H */