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 */ 59