Sam Grove / checksum

Utility functions for working with data streams

Example usage:

http://andy.dynamicbits.com/hdradio/

#include "mbed.h"
#include "checksum.h"

DigitalOut myled(LED1);

template <int T>
struct data{
    uint8_t buf[T];
    uint8_t checksum;
};

data<12> all_ones = {{1,1,1,1,1,1,1,1,1,1,1,1}};

int main() 
{
    calculateChecksum( all_ones.buf, sizeof(all_ones) );
      
    for(int i=0; i<sizeof(all_ones); i++)
    {
        printf("%02d: %d\n", i, *(all_ones.buf+i));
    }

    printf("checksum test: %s\n", (result)?"passed":"failed");

    while(1) 
    {
        myled = 1;
        wait(0.2);
        myled = 0;
        wait(0.2);
    }
}

checksum.cpp

Committer:
sam_grove
Date:
2013-03-07
Revision:
1:ace4b3aef52b
Parent:
0:39b5762958a4

File content as of revision 1:ace4b3aef52b:

/**
 * @file    checksum.cpp
 * @brief   Utility Function - Data integrity helpers
 * @author  sam grove
 * @version 1.0
 *
 * Copyright (c) 2013
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
#include "checksum.h"

bool validateChecksum( uint8_t const *pkt, uint32_t const length )
{
    uint32_t pos = 0;
    uint8_t sum = 0;
    while ( pos < (length-1) )
    {
        sum += *(pkt+pos++);
    }
    sum = 0x0 - sum;
    // return 0 or 1 based on the checksum test
    return (sum == *(pkt+pos)) ? 1 : 0;
}

void calculateChecksum( uint8_t *pkt, uint32_t const length )
{
    uint32_t pos = 0;
    uint8_t sum = 0;
    while ( pos < (length-1) )
    {
        sum += *(pkt+pos++);
    }    
    // put the checksum into the data stream
    *(pkt+pos) = 0x0 - sum;
    
    return;
}