qvalue.h

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/*
 * $Id: qvalue.h 4518 2008-07-28 15:39:28Z henningw $
 *
 * Handling of the q value
 *
 * Copyright (C) 2004 FhG FOKUS
 *
 * This file is part of Kamailio, a free SIP server.
 *
 * Kamailio 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
 *
 * Kamailio 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/*!
 * \file
 * \brief Functions related to the SIP q value
 */

#ifndef _QVALUE_H
#define _QVALUE_H 1

#include <string.h>

/*! \page QvalueHandling Q Value Handling
 * 
 * The q value expresses the priority of a URI within a set of URIs
 * (Contact header field in the same SIP message or dset array in
 * ser. The higher is the q value of a URI the higher is the priority
 * of the URI.
 *
 * The q value is usually expressed as a floating point number with
 * limited number of decimal digits, for example 0.346. RFC3261 allows
 * 0-3 decimal digits.
 *
 * To speed things up we represent the q value as integer number, it
 * is then easier to handle/print the value. To convert float into
 * integer we multiply the q value by 1000, i.e.
 * (float)0.567 == (int)567. In the opposite direction, values
 * higher or equal to 1000 are converted to 1.0 and values below or
 * equal to 0 are converted to 0.
 *
 * Value Q_UNSPECIFIED (which is in fact -1) has a special meaning, it
 * means that the q value is not known and the parameter should not be
 * printed when printing Contacts, implementations will then use
 * implementation specific pre-defined values.
 */

typedef int qvalue_t;

/*! \brief
 * Use this if the value of q is not specified
 */
#define Q_UNSPECIFIED ((qvalue_t)-1)


#define MAX_Q ((qvalue_t)1000)
#define MIN_Q ((qvalue_t)0)

#define MAX_Q_STR "1"
#define MAX_Q_STR_LEN (sizeof(MAX_Q_STR) - 1)

#define MIN_Q_STR "0"
#define MIN_Q_STR_LEN (sizeof(MIN_Q_STR) - 1)

#define Q_PREFIX "0."
#define Q_PREFIX_LEN (sizeof(Q_PREFIX) - 1)



/*! \brief
 * Calculate the length of printed q
 */
static inline size_t len_q(qvalue_t q)
{
   if (q == Q_UNSPECIFIED) {
      return 0;
   } else if (q >= MAX_Q) {
      return MAX_Q_STR_LEN;
   } else if (q <= MIN_Q) {
      return MIN_Q_STR_LEN;
   } else if (q % 100 == 0) {
      return Q_PREFIX_LEN + 1;
   } else if (q % 10 == 0) {
      return Q_PREFIX_LEN + 2;
   } else {
      return Q_PREFIX_LEN + 3;
   }
}


/*! \brief
 * Convert qvalue_t to double
 */
static inline double q2double(qvalue_t q)
{
   if (q == Q_UNSPECIFIED) {
      return -1;
   } else {
      return (double)((double)q / (double)1000);
   }
}


/*! \brief
 * Convert double to qvalue_t
 */
static inline qvalue_t double2q(double q)
{
   if (q == -1) {
      return Q_UNSPECIFIED;
   } else {
      return q * 1000;
   }
}


/*! \brief
 * Convert q value to string
 */
static inline char* q2str(qvalue_t q, unsigned int* len)
{
   static char buf[sizeof("0.123")];
   char* p;

   p = buf;
   if (q == Q_UNSPECIFIED) {
           /* Do nothing */
   } else if (q >= MAX_Q) {
      memcpy(p, MAX_Q_STR, MAX_Q_STR_LEN);
      p += MAX_Q_STR_LEN;
   } else if (q <= MIN_Q) {
      memcpy(p, MIN_Q_STR, MIN_Q_STR_LEN);
      p += MIN_Q_STR_LEN;
   } else {
      memcpy(p, Q_PREFIX, Q_PREFIX_LEN);
      p += Q_PREFIX_LEN;
      
      *p++ = q / 100 + '0';
      q %= 100;
      if (!q) goto end;

      *p++ = q / 10 + '0';
      q %= 10;
      if (!q) goto end;

      *p++ = q + '0';
   }
 end:
   *p = '\0';
   if (len) {
      *len = p - buf;
   }
   return buf;
}


/*! \brief
 * Convert string representation of q parameter in qvalue_t
 */
int str2q(qvalue_t* q, char* s, int len);


#endif /* _QVALUE_H */

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