checksum.cpp

00001 /**
00002  * @file    checksum.cpp
00003  * @brief   Utility Function - Data integrity helpers
00004  * @author  sam grove
00005  * @version 1.0
00006  *
00007  * Copyright (c) 2013
00008  *
00009  * Licensed under the Apache License, Version 2.0 (the "License");
00010  * you may not use this file except in compliance with the License.
00011  * You may obtain a copy of the License at
00012  *
00013  *     http://www.apache.org/licenses/LICENSE-2.0
00014  *
00015  * Unless required by applicable law or agreed to in writing, software
00016  * distributed under the License is distributed on an "AS IS" BASIS,
00017  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00018  * See the License for the specific language governing permissions and
00019  * limitations under the License.
00020  */
00021  
00022 #include "checksum.h"
00023 
00024 bool validateChecksum( uint8_t const *pkt, uint32_t const length )
00025 {
00026     uint32_t pos = 0;
00027     uint8_t sum = 0;
00028     while ( pos < (length-1) )
00029     {
00030         sum += *(pkt+pos++);
00031     }
00032     sum = 0x0 - sum;
00033     // return 0 or 1 based on the checksum test
00034     return (sum == *(pkt+pos)) ? 1 : 0;
00035 }
00036 
00037 void calculateChecksum( uint8_t *pkt, uint32_t const length )
00038 {
00039     uint32_t pos = 0;
00040     uint8_t sum = 0;
00041     while ( pos < (length-1) )
00042     {
00043         sum += *(pkt+pos++);
00044     }    
00045     // put the checksum into the data stream
00046     *(pkt+pos) = 0x0 - sum;
00047     
00048     return;
00049 }
00050