[linux.git] / include / linux / circ_buf.h

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * See Documentation/core-api/circular-buffers.rst for more information.
 */

#ifndef _LINUX_CIRC_BUF_H
#define _LINUX_CIRC_BUF_H 1

struct circ_buf {
	char *buf;
	int head;
	int tail;
};

/* Return count in buffer.  */
#define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))

/* Return space available, 0..size-1.  We always leave one free char
   as a completely full buffer has head == tail, which is the same as
   empty.  */
#define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))

/* Return count up to the end of the buffer.  Carefully avoid
   accessing head and tail more than once, so they can change
   underneath us without returning inconsistent results.  */
#define CIRC_CNT_TO_END(head,tail,size) \
	({int end = (size) - (tail); \
	  int n = ((head) + end) & ((size)-1); \
	  n < end ? n : end;})

/* Return space available up to the end of the buffer.  */
#define CIRC_SPACE_TO_END(head,tail,size) \
	({int end = (size) - 1 - (head); \
	  int n = (end + (tail)) & ((size)-1); \
	  n <= end ? n : end+1;})

#endif /* _LINUX_CIRC_BUF_H  */
Commit	Line	Data
b2441318	1	/* SPDX-License-Identifier: GPL-2.0 */
90fddabf	2	/*
5fb94e9c	3	* See Documentation/core-api/circular-buffers.rst for more information.
90fddabf DH	4	*/
90fddabf DH	5
1da177e4 LT	6	#ifndef _LINUX_CIRC_BUF_H
	7	#define _LINUX_CIRC_BUF_H 1
	8
	9	struct 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 */