Make the ring buffer a two-state buffer (supplier and consumer)

[unix-history] / usr / src / usr.bin / telnet / ring.c

/*
* 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))


/*
* 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;
}

/*
* 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;
{
   ring->consume = ring_increment(ring, ring->consume, count);
   ring->consumetime = ++ring_clock;
}



/* 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);
   }
}

/* number of bytes that are available for consuming */
int
ring_full_count(ring)
Ring *ring;
{
   if (ring_full(ring)) {
       return ring->size;      /* nothing consumed, but full */
   } else {
       return ring_subtract(ring, ring->supply, ring->consume);
   }
}

/* number of CONSECUTIVE bytes available for consuming */
int
ring_full_consecutive(ring)
Ring *ring;
{
   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);
   }
}

/*
* 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;
   }
}

/* Mark routines */

/* XXX do something here */
void
ring_mark(ring)
Ring *ring;
{
}

int
ring_at_mark(ring)
Ring *ring;
{
   return 0;
}

void
ring_clear_mark(ring)
Ring *ring;
{
}