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fifo.c

/*
 * A simple kernel FIFO implementation.
 *
 * Copyright (C) 2004 Stelian Pop <stelian@popies.net>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "fifo.h"

struct fifo *fifo_alloc(unsigned int size)
{
      struct fifo *fifo;

      fifo = malloc(sizeof(struct fifo));
      if (!fifo)
            return 0;

      fifo->buffer = malloc(size);
      fifo->size = size;
      fifo->in = fifo->out = 0;

      return fifo;
}

void fifo_free(struct fifo *fifo)
{
      free(fifo->buffer);
      free(fifo);
}

unsigned int fifo_put(struct fifo *fifo, void *buffer, unsigned int len)
{
      unsigned int l;

      len = min(len, fifo_room(fifo));

      /* first put the data starting from fifo->in to buffer end */
      l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));
      memcpy(fifo->buffer + (fifo->in & (fifo->size - 1)), buffer, l);

      /* then put the rest (if any) at the beginning of the buffer */
      memcpy(fifo->buffer, buffer + l, len - l);

      /*
       * Ensure that we add the bytes to the fifo -before-
       * we update the fifo->in index.
       */

      fifo->in += len;

      return len;
}

unsigned int fifo_get(struct fifo *fifo, void *buf, unsigned int len)
{
      len = min(len, fifo->in - fifo->out);

      if (buf) {
            unsigned int l;

            /*
             * first get the data from fifo->out until the end of the buffer
             */
            l = min(len, fifo->size - (fifo->out & (fifo->size - 1)));
            memcpy(buf, fifo->buffer + (fifo->out & (fifo->size - 1)), l);

            /*
             * then get the rest (if any) from the beginning of the buffer
             */
            memcpy(buf + l, fifo->buffer, len - l);
      }

      fifo->out += len;

      if (fifo->in == fifo->out)
            fifo->in = fifo->out = 0;

      return len;
}

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