encodePacket.c

00001 /**
00002  * Rapid-prototyping protection schemes with IEC 61850
00003  *
00004  * Copyright (c) 2012 Steven Blair
00005  *
00006  * This program is free software; you can redistribute it and/or
00007  * modify it under the terms of the GNU General Public License
00008  * as published by the Free Software Foundation; either version 2
00009  * of the License, or (at your option) any later version.
00010 
00011  * This program is distributed in the hope that it will be useful,
00012  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00013  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014  * GNU General Public License for more details.
00015 
00016  * You should have received a copy of the GNU General Public License
00017  * along with this program; if not, write to the Free Software
00018  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
00019  */
00020 
00021 #include "encodePacket.h"
00022 #include "svEncodeBasic.h"
00023 
00024 int getLengthBytes(int len) {
00025     if (len <= 126) {
00026         return 1;
00027     }
00028     else if (len <= 255) {
00029         return 2;
00030     }
00031     else {
00032         return 3;
00033     }
00034 }
00035 
00036 int encodeLength(unsigned char *buf, CTYPE_INT16U len) {
00037     if (len <= 126) {
00038         buf[0] = (unsigned char) len;
00039         return 1;
00040     }
00041     else if (len <= 255) {
00042         buf[0] = (unsigned char) 0x81;            // 0x80 specifies larger than one byte; 0x02 is number of length bytes to follow
00043         buf[1] = (unsigned char) len;
00044 
00045         return 2;
00046     }
00047     else {
00048         // assume length is not greater than 2^15
00049         buf[0] = (unsigned char) 0x82;            // 0x80 specifies larger than one byte; 0x02 is number of length bytes to follow
00050         ENCODE_CTYPE_INT16U(&buf[1], &len);
00051 
00052         return 3;
00053     }
00054 }