qvalue.h
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 /*
  * $Id$
  *
  * Handling of the q value
  *
  * Copyright (C) 2004 FhG FOKUS
  *
  * This file is part of ser, a free SIP server.
  *
  * ser 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
  *
  * For a license to use the ser software under conditions
  * other than those described here, or to purchase support for this
  * software, please contact iptel.org by e-mail at the following addresses:
  *    info@iptel.org
  *
  * ser 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
  *
  * History
  * ------
  * 2004-04-25 created (janakj)
  */
 
 #ifndef _QVALUE_H
 #define _QVALUE_H 1
 
 #include <string.h>
 
 /*
  * 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;
 
 /*
  * 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)
 
 
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 /*
  * 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;
 	}
 }
 
 
 /*
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  * 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);
 	}
 }
 
 
 /*
  * Convert double to qvalue_t
  */
 static inline qvalue_t double2q(double q)
 {
 	if (q == -1) {
 		return Q_UNSPECIFIED;
 	} else {
 		return q * 1000;
 	}
 }
 
 
 /*
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  * Convert q value to string
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  */
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 static inline char* q2str(qvalue_t q, unsigned int* len)
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 {
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 	static char buf[sizeof("0.123")];
 	char* p;
 
 	p = buf;
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 	if (q == Q_UNSPECIFIED) {
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 		     /* Do nothing */
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 	} else if (q >= MAX_Q) {
 		memcpy(p, MAX_Q_STR, MAX_Q_STR_LEN);
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 		p += MAX_Q_STR_LEN;
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 	} else if (q <= MIN_Q) {
 		memcpy(p, MIN_Q_STR, MIN_Q_STR_LEN);
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 		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;
 
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 		*p++ = q + '0';
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 	}
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  end:
 	*p = '\0';
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 	if (len) {
 		*len = p - buf;
 	}
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 	return buf;
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 }
 
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 /*
  * Convert string representation of q parameter in qvalue_t
  */
 int str2q(qvalue_t* q, char* s, int len);
 
 
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 #endif /* _QVALUE_H */