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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_H7#define _LINUX_CIRC_BUF_H 18 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 char19 as a completely full buffer has head == tail, which is the same as20 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 avoid24 accessing head and tail more than once, so they can change25 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