queue.c

srtp 1.0.1 比较适用于头一次看。其他版本的有需要也可以传上来。

/*
 * queue.c 
 *
 * a byte queue, for buffering keystream and other data
 *
 * David A. McGrew
 * Cisco Systems, Inc.
 *
 */

#include "err.h"

/*
 * An octet_queue_t is a circular buffer holding some data.  There
 * are four pointers:
 *
 * start    the start of the buffer
 * end      the end of the buffer
 * input    the position of the next data to be input to the queue
 * output   the position of the next data to be output from the queue
 *
 * Here's a diagram, with Xs indicating data in the buffer:
 *  
 *  +---------------+--------------------------------+---------------+
 *  |XXXXXXXXXXXXXXX|                                |XXXXXXXXXXXXXXX|
 *  +---------------+--------------------------------+---------------+
 *  ^               ^                                ^               ^
 *  |               |                                |               |
 *  start           input                            output          end 
 *
 * 
 *  Any number of octets can be output, but at least QUEUE_INPUT_MIN
 *  octets must be entered at a time.
 *
 *
 */


typedef struct {
  octet_t *start, *end, *input, *output;
  int length, data;
} octet_queue_t;


err_status_t
octet_queue_alloc(octet_queue_t **queue, int len_octets) {
  octet_t *pointer;
  octet_queue_t *q;
  
  pointer = malloc(len_octets + sizeof(octet_queue_t));
  if (!pointer)
    return err_status_alloc_err;

  q = (octet_queue_t *)pointer;
  q->start  = pointer + sizeof(octet_queue_t);
  q->end    = q->start + len_octets;
  q->input  = q->start;
  q->output = NULL;    
  
}