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);
    }
}

Diff: checksum.cpp

Revision:
0:39b5762958a4
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/checksum.cpp	Thu Mar 07 20:55:29 2013 +0000
@@ -0,0 +1,50 @@
+/**
+ * @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;
+}
+