source: mainline/uspace/lib/c/include/adt/fifo.h@ d7f7a4a

/*
 * SPDX-FileCopyrightText: 2006 Jakub Jermar
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

/** @addtogroup libc
 * @{
 */
/** @file
 */

/*
 * This implementation of FIFO stores values in an array
 * (static or dynamic). As such, these FIFOs have upper bound
 * on number of values they can store. Push and pop operations
 * are done via accessing the array through head and tail indices.
 * Because of better operation ordering in fifo_pop(), the access
 * policy for these two indices is to 'increment (mod size of FIFO)
 * and use'.
 */

#ifndef _LIBC_FIFO_H_
#define _LIBC_FIFO_H_

#include <stdlib.h>

typedef unsigned long fifo_count_t;
typedef unsigned long fifo_index_t;

#define FIFO_CREATE_STATIC(name, t, itms) \
        struct { \
                t fifo[(itms)]; \
                fifo_count_t items; \
                fifo_index_t head; \
                fifo_index_t tail; \
        } name

/** Create and initialize static FIFO.
 *
 * FIFO is allocated statically.
 * This macro is suitable for creating smaller FIFOs.
 *
 * @param name Name of FIFO.
 * @param t Type of values stored in FIFO.
 * @param itms Number of items that can be stored in FIFO.
 */
#define FIFO_INITIALIZE_STATIC(name, t, itms)           \
        FIFO_CREATE_STATIC(name, t, itms) = {           \
                .items = (itms),                        \
                .head = 0,                              \
                .tail = 0                               \
        }

/** Create and prepare dynamic FIFO.
 *
 * FIFO is allocated dynamically.
 * This macro is suitable for creating larger FIFOs.
 *
 * @param name Name of FIFO.
 * @param t Type of values stored in FIFO.
 * @param itms Number of items that can be stored in FIFO.
 */
#define FIFO_INITIALIZE_DYNAMIC(name, t, itms)          \
        struct {                                        \
                t *fifo;                                \
                fifo_count_t items;                     \
                fifo_index_t head;                      \
                fifo_index_t tail;                      \
        } name = {                                      \
                .fifo = NULL,                           \
                .items = (itms),                        \
                .head = 0,                              \
                .tail = 0                               \
        }

/** Pop value from head of FIFO.
 *
 * @param name FIFO name.
 *
 * @return Leading value in FIFO.
 */
#define fifo_pop(name) \
        name.fifo[name.head = (name.head + 1) < name.items ? (name.head + 1) : 0]

/** Push value to tail of FIFO.
 *
 * @param name FIFO name.
 * @param value Value to be appended to FIFO.
 *
 */
#define fifo_push(name, value) \
        name.fifo[name.tail = (name.tail + 1) < name.items ? (name.tail + 1) : 0] = (value)

/** Allocate memory for dynamic FIFO.
 *
 * @param name FIFO name.
 */
#define fifo_create(name) \
        name.fifo = malloc(sizeof(*name.fifo) * name.items)

#endif

/** @}
 */