Andrew Boyson / net

A stack which works with or without an Mbed os library. Provides IPv4 or IPv6 with a full 1500 byte buffer.

Dependents:   oldheating gps motorhome heating

checksum.c@151:bde6f7da1755, 2019-07-19 (annotated)

Committer:
andrewboyson
Date:
Fri Jul 19 17:48:06 2019 +0000
Revision:
151:bde6f7da1755
Parent:
136:8a65abb0dc63 
Removed private key and certificate from semihost storage as found to be unreliable (though secure) and moved it into flash storage (reliable, simple, but visible on mbed.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
andrewboyson 136:8a65abb0dc63 1 #include <stdint.h>
andrewboyson 136:8a65abb0dc63 2
andrewboyson 136:8a65abb0dc63 3 /*
andrewboyson 136:8a65abb0dc63 4 Checksum is calculated on 2 byte chunks
andrewboyson 136:8a65abb0dc63 5 All the routines below rely on the start being at a 2 byte boundary
andrewboyson 136:8a65abb0dc63 6 It makes no sence for any, other than the last, call to accumulate the checksum to have an odd number of bytes
andrewboyson 136:8a65abb0dc63 7
andrewboyson 136:8a65abb0dc63 8 Start the first call with a sum of zero.
andrewboyson 136:8a65abb0dc63 9 Thereafter propagate it to each subsequent call.
andrewboyson 136:8a65abb0dc63 10 Always call the Fin routine for the last call to roll back in any carries, to convert to 16 bit and to take the ones complement.
andrewboyson 136:8a65abb0dc63 11 The Fin call can have an odd number of byes but cannot invert.
andrewboyson 136:8a65abb0dc63 12
andrewboyson 136:8a65abb0dc63 13 The simple CheckSum is for when there is just one lump of data to calculate the checksum over.
andrewboyson 136:8a65abb0dc63 14
andrewboyson 136:8a65abb0dc63 15 If the lump of data starts at an odd address the 2 byte cast will result in an unaligned access.
andrewboyson 136:8a65abb0dc63 16 This is ok for the LPC1768 M3, it just takes it a bit longer, but could cause other processors to fault.
andrewboyson 136:8a65abb0dc63 17 It should never happen as no protocol is not at least aligned on even bytes and the buffers all start aligned.
andrewboyson 136:8a65abb0dc63 18 */
andrewboyson 136:8a65abb0dc63 19
andrewboyson 136:8a65abb0dc63 20 uint32_t CheckSumAddDirect(uint32_t sum, int count, void* pData)
andrewboyson 136:8a65abb0dc63 21 {
andrewboyson 136:8a65abb0dc63 22 uint16_t* p = (uint16_t*)pData; //Set up a 16 bit pointer for the data
andrewboyson 136:8a65abb0dc63 23
andrewboyson 136:8a65abb0dc63 24 while(count > 1)
andrewboyson 136:8a65abb0dc63 25 {
andrewboyson 136:8a65abb0dc63 26 sum += *p++; // Add each pair of bytes into 32 bit accumulator
andrewboyson 136:8a65abb0dc63 27 count -= 2;
andrewboyson 136:8a65abb0dc63 28 }
andrewboyson 136:8a65abb0dc63 29 if (count) sum += *(uint8_t*) p; // Add left-over byte, if any
andrewboyson 136:8a65abb0dc63 30 return sum;
andrewboyson 136:8a65abb0dc63 31 }
andrewboyson 136:8a65abb0dc63 32 uint32_t CheckSumAddInvert(uint32_t sum, int count, void* pData)
andrewboyson 136:8a65abb0dc63 33 {
andrewboyson 136:8a65abb0dc63 34 uint16_t* p = (uint16_t*)pData; //Set up a 16 bit pointer for the data
andrewboyson 136:8a65abb0dc63 35
andrewboyson 136:8a65abb0dc63 36 while(count > 1)
andrewboyson 136:8a65abb0dc63 37 {
andrewboyson 136:8a65abb0dc63 38 uint16_t value = (*p & 0xFF00) >> 8; // Invert the value
andrewboyson 136:8a65abb0dc63 39 value |= (*p & 0x00FF) << 8;
andrewboyson 136:8a65abb0dc63 40 p++;
andrewboyson 136:8a65abb0dc63 41 sum += value; // Add each pair of bytes into 32 bit accumulator
andrewboyson 136:8a65abb0dc63 42 count -= 2;
andrewboyson 136:8a65abb0dc63 43 }
andrewboyson 136:8a65abb0dc63 44 if (count) sum += *(uint8_t*) p; // Add left-over byte, if any
andrewboyson 136:8a65abb0dc63 45 return sum;
andrewboyson 136:8a65abb0dc63 46 }
andrewboyson 136:8a65abb0dc63 47 uint16_t CheckSumFinDirect(uint32_t sum, int count, void* pData)
andrewboyson 136:8a65abb0dc63 48 {
andrewboyson 136:8a65abb0dc63 49 sum = CheckSumAddDirect(sum, count, pData);
andrewboyson 136:8a65abb0dc63 50 while (sum>>16) sum = (sum & 0xffff) + (sum >> 16); // Add any carries from the sum back into the sum to make it ones complement
andrewboyson 136:8a65abb0dc63 51 return ~sum;
andrewboyson 136:8a65abb0dc63 52 }
andrewboyson 136:8a65abb0dc63 53 uint16_t CheckSum(int count, void* pData)
andrewboyson 136:8a65abb0dc63 54 {
andrewboyson 136:8a65abb0dc63 55 return CheckSumFinDirect(0, count, pData);
andrewboyson 136:8a65abb0dc63 56 }