usr/src/usr.bin/telnet/ring.c

/*
 * Copyright (c) 1988 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#ifndef lint
static char sccsid[] = "@(#)ring.c      1.10 (Berkeley) %G%";
#endif /* not lint */

/*
 * This defines a structure for a ring buffer.
 *
 * The circular buffer has two parts:
 *(((
 *      full:   [consume, supply)
 *      empty:  [supply, consume)
 *]]]
 *
 */

#include        <stdio.h>
#include        <errno.h>

#ifdef  size_t
#undef  size_t
#endif

#include        <sys/types.h>
#include        <sys/ioctl.h>
#include        <sys/socket.h>

#include        "ring.h"
#include        "general.h"

/* Internal macros */

#if     !defined(MIN)
#define MIN(a,b)        (((a)<(b))? (a):(b))
#endif  /* !defined(MIN) */

#define ring_subtract(d,a,b)    ((((int)(a))-((int)(b)) >= 0)? \
                                        (a)-(b): (((a)-(b))+(d)->size))

#define ring_increment(d,a,c)   (((a)+(c) < (d)->top)? \
                                        (a)+(c) : (((a)+(c))-(d)->size))

#define ring_decrement(d,a,c)   (((a)-(c) >= (d)->bottom)? \
                                        (a)-(c) : (((a)-(c))-(d)->size))


/*
 * The following is a clock, used to determine full, empty, etc.
 *
 * There is some trickiness here.  Since the ring buffers are initialized
 * to ZERO on allocation, we need to make sure, when interpreting the
 * clock, that when the times are EQUAL, then the buffer is FULL.
 */
static u_long ring_clock = 0;


#define ring_empty(d) (((d)->consume == (d)->supply) && \
                                ((d)->consumetime >= (d)->supplytime))
#define ring_full(d) (((d)->supply == (d)->consume) && \
                                ((d)->supplytime > (d)->consumetime))


/* Buffer state transition routines */

ring_init(ring, buffer, count)
Ring *ring;
char *buffer;
int count;
{
    memset((char *)ring, 0, sizeof *ring);

    ring->size = count;

    ring->supply = ring->consume = ring->bottom = buffer;

    ring->top = ring->bottom+ring->size;

    return 1;
}

/* Mark routines */

/*
 * Mark the most recently supplied byte.
 */

void
ring_mark(ring)
Ring *ring;
{
    ring->mark = ring_decrement(ring, ring->supply, 1);
}

/*
 * Is the ring pointing to the mark?
 */

int
ring_at_mark(ring)
Ring *ring;
{
    if (ring->mark == ring->consume) {
        return 1;
    } else {
        return 0;
    }
}

/*
 * Clear any mark set on the ring.
 */

void
ring_clear_mark(ring)
Ring *ring;
{
    ring->mark = 0;
}

/*
 * Add characters from current segment to ring buffer.
 */
void
ring_supplied(ring, count)
Ring *ring;
int count;
{
    ring->supply = ring_increment(ring, ring->supply, count);
    ring->supplytime = ++ring_clock;
}

/*
 * We have just consumed "c" bytes.
 */
void
ring_consumed(ring, count)
Ring *ring;
int count;
{
    if (count == 0)     /* don't update anything */
        return;

    if (ring->mark &&
                (ring_subtract(ring, ring->mark, ring->consume) < count)) {
        ring->mark = 0;
    }
    ring->consume = ring_increment(ring, ring->consume, count);
    ring->consumetime = ++ring_clock;
    /*
     * Try to encourage "ring_empty_consecutive()" to be large.
     */
    if (ring_empty(ring)) {
        ring->consume = ring->supply = ring->bottom;
    }
}


/* Buffer state query routines */


/* Number of bytes that may be supplied */
int
ring_empty_count(ring)
Ring *ring;
{
    if (ring_empty(ring)) {     /* if empty */
            return ring->size;
    } else {
        return ring_subtract(ring, ring->consume, ring->supply);
    }
}

/* number of CONSECUTIVE bytes that may be supplied */
int
ring_empty_consecutive(ring)
Ring *ring;
{
    if ((ring->consume < ring->supply) || ring_empty(ring)) {
                            /*
                             * if consume is "below" supply, or empty, then
                             * return distance to the top
                             */
        return ring_subtract(ring, ring->top, ring->supply);
    } else {
                                    /*
                                     * else, return what we may.
                                     */
        return ring_subtract(ring, ring->consume, ring->supply);
    }
}

/* Return the number of bytes that are available for consuming
 * (but don't give more than enough to get to cross over set mark)
 */

int
ring_full_count(ring)
Ring *ring;
{
    if ((ring->mark == 0) || (ring->mark == ring->consume)) {
        if (ring_full(ring)) {
            return ring->size;  /* nothing consumed, but full */
        } else {
            return ring_subtract(ring, ring->supply, ring->consume);
        }
    } else {
        return ring_subtract(ring, ring->mark, ring->consume);
    }
}

/*
 * Return the number of CONSECUTIVE bytes available for consuming.
 * However, don't return more than enough to cross over set mark.
 */
int
ring_full_consecutive(ring)
Ring *ring;
{
    if ((ring->mark == 0) || (ring->mark == ring->consume)) {
        if ((ring->supply < ring->consume) || ring_full(ring)) {
            return ring_subtract(ring, ring->top, ring->consume);
        } else {
            return ring_subtract(ring, ring->supply, ring->consume);
        }
    } else {
        if (ring->mark < ring->consume) {
            return ring_subtract(ring, ring->top, ring->consume);
        } else {        /* Else, distance to mark */
            return ring_subtract(ring, ring->mark, ring->consume);
        }
    }
}

/*
 * Move data into the "supply" portion of of the ring buffer.
 */
void
ring_supply_data(ring, buffer, count)
Ring *ring;
char *buffer;
int count;
{
    int i;

    while (count) {
        i = MIN(count, ring_empty_consecutive(ring));
        memcpy(ring->supply, buffer, i);
        ring_supplied(ring, i);
        count -= i;
        buffer += i;
    }
}


/*
 * Move data from the "consume" portion of the ring buffer
 */
void
ring_consume_data(ring, buffer, count)
Ring *ring;
char *buffer;
int count;
{
    int i;

    while (count) {
        i = MIN(count, ring_full_consecutive(ring));
        memcpy(buffer, ring->consume, i);
        ring_consumed(ring, i);
        count -= i;
        buffer += i;
    }
}