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@200:5acbc41bf469, 2021-05-20 (annotated)

Committer:
andrewboyson
Date:
Thu May 20 14:32:52 2021 +0000
Revision:
200:5acbc41bf469
Parent:
136:8a65abb0dc63 
Increased number of arp entries from 20 to 30 to accommodate the number of WIZ devices plus a few incoming port 80 calls from the internet.

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 }