Reputation: 183
I was hoping someone might be able to shed some light on why my CRC-16 implementation does not seem to run correctly on Visual Studio? I got the algorithm from a manual for a specific device, and wrote the int main() myself. There are always 'type' errors when I try to pass the arguments to the function, so I suspect there is something wrong with the format? This is the info that came with the code:
Test CRC for string "123456789" : 5502 (hex)
#include <stdio.h>
unsigned int crctable[256] =
{
0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF,
0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7,
0x0919, 0x1890, 0x2A0B, 0x3B82, 0x4F3D, 0x5EB4, 0x6C2F, 0x7DA6,
0x8551, 0x94D8, 0xA643, 0xB7CA, 0xC375, 0xD2FC, 0xE067, 0xF1EE,
0x1232, 0x03BB, 0x3120, 0x20A9, 0x5416, 0x459F, 0x7704, 0x668D,
0x9E7A, 0x8FF3, 0xBD68, 0xACE1, 0xD85E, 0xC9D7, 0xFB4C, 0xEAC5,
0x1B2B, 0x0AA2, 0x3839, 0x29B0, 0x5D0F, 0x4C86, 0x7E1D, 0x6F94,
0x9763, 0x86EA, 0xB471, 0xA5F8, 0xD147, 0xC0CE, 0xF255, 0xE3DC,
0x2464, 0x35ED, 0x0776, 0x16FF, 0x6240, 0x73C9, 0x4152, 0x50DB,
0xA82C, 0xB9A5, 0x8B3E, 0x9AB7, 0xEE08, 0xFF81, 0xCD1A, 0xDC93,
0x2D7D, 0x3CF4, 0x0E6F, 0x1FE6, 0x6B59, 0x7AD0, 0x484B, 0x59C2,
0xA135, 0xB0BC, 0x8227, 0x93AE, 0xE711, 0xF698, 0xC403, 0xD58A,
0x3656, 0x27DF, 0x1544, 0x04CD, 0x7072, 0x61FB, 0x5360, 0x42E9,
0xBA1E, 0xAB97, 0x990C, 0x8885, 0xFC3A, 0xEDB3, 0xDF28, 0xCEA1,
0x3F4F, 0x2EC6, 0x1C5D, 0x0DD4, 0x796B, 0x68E2, 0x5A79, 0x4BF0,
0xB307, 0xA28E, 0x9015, 0x819C, 0xF523, 0xE4AA, 0xD631, 0xC7B8,
0x48C8, 0x5941, 0x6BDA, 0x7A53, 0x0EEC, 0x1F65, 0x2DFE, 0x3C77,
0xC480, 0xD509, 0xE792, 0xF61B, 0x82A4, 0x932D, 0xA1B6, 0xB03F,
0x41D1, 0x5058, 0x62C3, 0x734A, 0x07F5, 0x167C, 0x24E7, 0x356E,
0xCD99, 0xDC10, 0xEE8B, 0xFF02, 0x8BBD, 0x9A34, 0xA8AF, 0xB926,
0x5AFA, 0x4B73, 0x79E8, 0x6861, 0x1CDE, 0x0D57, 0x3FCC, 0x2E45,
0xD6B2, 0xC73B, 0xF5A0, 0xE429, 0x9096, 0x811F, 0xB384, 0xA20D,
0x53E3, 0x426A, 0x70F1, 0x6178, 0x15C7, 0x044E, 0x36D5, 0x275C,
0xDFAB, 0xCE22, 0xFCB9, 0xED30, 0x998F, 0x8806, 0xBA9D, 0xAB14,
0x6CAC, 0x7D25, 0x4FBE, 0x5E37, 0x2A88, 0x3B01, 0x099A, 0x1813,
0xE0E4, 0xF16D, 0xC3F6, 0xD27F, 0xA6C0, 0xB749, 0x85D2, 0x945B,
0x65B5, 0x743C, 0x46A7, 0x572E, 0x2391, 0x3218, 0x0083, 0x110A,
0xE9FD, 0xF874, 0xCAEF, 0xDB66, 0xAFD9, 0xBE50, 0x8CCB, 0x9D42,
0x7E9E, 0x6F17, 0x5D8C, 0x4C05, 0x38BA, 0x2933, 0x1BA8, 0x0A21,
0xF2D6, 0xE35F, 0xD1C4, 0xC04D, 0xB4F2, 0xA57B, 0x97E0, 0x8669,
0x7787, 0x660E, 0x5495, 0x451C, 0x31A3, 0x202A, 0x12B1, 0x0338,
0xFBCF, 0xEA46, 0xD8DD, 0xC954, 0xBDEB, 0xAC62, 0x9EF9, 0x8F70
};
unsigned int // Returns Calculated CRC value
CalculateCRC16(
unsigned int crc_seed, // Seed for CRC calculation
void *c_ptr, // Pointer to byte array to perform CRC on
unsigned int len) // Number of bytes to CRC
{
unsigned char *c = c_ptr;
unsigned int crc = crc_seed;
while (len--){
crc = (crc << 8) ^ crctable[((crc >> 8) ^ *c++)];
printf("%d", crc);
}
return (crc);
}
int main(){
printf("%d", CalculateCRC16(0xFFFF, "123456789", 2));
return 0;
}
Upvotes: 7
Views: 46490
Reputation: 1
that table lists the powers of the polynomial, to avoid errors in the table calculate the powers during the calculation, and make the polynomial an entry as well as the initial value. Use Dartpad to simulate it: https://dartpad.dev/?null_safety=true
void main() {
final int polynomial = 0x1189;
final int initialValue = 0xFFFF;
String crc16(String expression, int polynomial, int initialValue) {
int checkSum = initialValue;
for (int i = 0; i < expression.length; i++) {
checkSum ^= (expression.codeUnitAt(i) << 8);
for (int j = 0; j < 8; j++) {
if (((checkSum <<= 1) & 0x10000) == 0x10000) checkSum ^= polynomial;
checkSum &= 0xFFFF;
}
}
return checkSum.toRadixString(16).toUpperCase();
}
print(crc16('123456789', polynomial, initialValue));
}
To be compliant to CRC16 CCITT you should use polynomial=0x1021 and initial value = 0xFFFF.
https://www.gatevidyalay.com/cyclic-redundancy-check-crc-error-detection/ has a good explanation about CRC.
Upvotes: 0
Reputation: 1
I have used the same CRC checks and in your code you need to change only the following line: crc = (crc >> 8) ^ crctable[(crc^(*c++))&0xFF];
Upvotes: 0
Reputation: 826
The table you are using appears to be incorrectly generated. The first sixteen entries are correct, but it diverges after that. I don't think you will have much luck decoding CCITT CRC-16 with it.
See CRC for cross platform applications for an example of the correctly-generated table.
Upvotes: 0
Reputation: 32953
On this line
crc = (crc << 8) ^ crctable[((crc >> 8) ^ *c++)];
the result of ((crc >> 8) ^ *c++)
can become > 255, and cause an access violation. Just make sure the result is always 0.255 by masking the index into crctable
crc = (crc << 8) ^ crctable[((crc >> 8) ^ *c++) & 0x00FF];
// but you will need to clean up the result as its upper 16 bits
// are not guaranteed to be all 0
return crc & 0xffff;
or better, the resulting crc value as it ensures that crc will never contain a value > 0x0000ffff
crc = ( (crc << 8) ^ crctable[((crc >> 8) ^ *c++)] ) & 0xffff;
and you'll be all set. The base of the issue is that the original code seems to be 16 bits code (where int
was 16 bits), and you are using a 32 bits compiler.
Upvotes: 1
Reputation: 12749
All cleaned up and ready to go:
#include <stdio.h>
#include <stdint.h>
static const uint16_t crctable[256] =
{
0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF,
0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7,
0x0919, 0x1890, 0x2A0B, 0x3B82, 0x4F3D, 0x5EB4, 0x6C2F, 0x7DA6,
0x8551, 0x94D8, 0xA643, 0xB7CA, 0xC375, 0xD2FC, 0xE067, 0xF1EE,
0x1232, 0x03BB, 0x3120, 0x20A9, 0x5416, 0x459F, 0x7704, 0x668D,
0x9E7A, 0x8FF3, 0xBD68, 0xACE1, 0xD85E, 0xC9D7, 0xFB4C, 0xEAC5,
0x1B2B, 0x0AA2, 0x3839, 0x29B0, 0x5D0F, 0x4C86, 0x7E1D, 0x6F94,
0x9763, 0x86EA, 0xB471, 0xA5F8, 0xD147, 0xC0CE, 0xF255, 0xE3DC,
0x2464, 0x35ED, 0x0776, 0x16FF, 0x6240, 0x73C9, 0x4152, 0x50DB,
0xA82C, 0xB9A5, 0x8B3E, 0x9AB7, 0xEE08, 0xFF81, 0xCD1A, 0xDC93,
0x2D7D, 0x3CF4, 0x0E6F, 0x1FE6, 0x6B59, 0x7AD0, 0x484B, 0x59C2,
0xA135, 0xB0BC, 0x8227, 0x93AE, 0xE711, 0xF698, 0xC403, 0xD58A,
0x3656, 0x27DF, 0x1544, 0x04CD, 0x7072, 0x61FB, 0x5360, 0x42E9,
0xBA1E, 0xAB97, 0x990C, 0x8885, 0xFC3A, 0xEDB3, 0xDF28, 0xCEA1,
0x3F4F, 0x2EC6, 0x1C5D, 0x0DD4, 0x796B, 0x68E2, 0x5A79, 0x4BF0,
0xB307, 0xA28E, 0x9015, 0x819C, 0xF523, 0xE4AA, 0xD631, 0xC7B8,
0x48C8, 0x5941, 0x6BDA, 0x7A53, 0x0EEC, 0x1F65, 0x2DFE, 0x3C77,
0xC480, 0xD509, 0xE792, 0xF61B, 0x82A4, 0x932D, 0xA1B6, 0xB03F,
0x41D1, 0x5058, 0x62C3, 0x734A, 0x07F5, 0x167C, 0x24E7, 0x356E,
0xCD99, 0xDC10, 0xEE8B, 0xFF02, 0x8BBD, 0x9A34, 0xA8AF, 0xB926,
0x5AFA, 0x4B73, 0x79E8, 0x6861, 0x1CDE, 0x0D57, 0x3FCC, 0x2E45,
0xD6B2, 0xC73B, 0xF5A0, 0xE429, 0x9096, 0x811F, 0xB384, 0xA20D,
0x53E3, 0x426A, 0x70F1, 0x6178, 0x15C7, 0x044E, 0x36D5, 0x275C,
0xDFAB, 0xCE22, 0xFCB9, 0xED30, 0x998F, 0x8806, 0xBA9D, 0xAB14,
0x6CAC, 0x7D25, 0x4FBE, 0x5E37, 0x2A88, 0x3B01, 0x099A, 0x1813,
0xE0E4, 0xF16D, 0xC3F6, 0xD27F, 0xA6C0, 0xB749, 0x85D2, 0x945B,
0x65B5, 0x743C, 0x46A7, 0x572E, 0x2391, 0x3218, 0x0083, 0x110A,
0xE9FD, 0xF874, 0xCAEF, 0xDB66, 0xAFD9, 0xBE50, 0x8CCB, 0x9D42,
0x7E9E, 0x6F17, 0x5D8C, 0x4C05, 0x38BA, 0x2933, 0x1BA8, 0x0A21,
0xF2D6, 0xE35F, 0xD1C4, 0xC04D, 0xB4F2, 0xA57B, 0x97E0, 0x8669,
0x7787, 0x660E, 0x5495, 0x451C, 0x31A3, 0x202A, 0x12B1, 0x0338,
0xFBCF, 0xEA46, 0xD8DD, 0xC954, 0xBDEB, 0xAC62, 0x9EF9, 0x8F70
};
uint16_t // Returns Calculated CRC value
CalculateCRC16(
uint16_t crc, // Seed for CRC calculation
const void *c_ptr, // Pointer to byte array to perform CRC on
size_t len) // Number of bytes to CRC
{
const uint8_t *c = c_ptr;
while (len--)
crc = (crc << 8) ^ crctable[((crc >> 8) ^ *c++)];
return crc;
}
int main()
{
printf("%04x\n", CalculateCRC16(0xFFFF, "123456789", 9));
return 0;
}
Upvotes: 6
Reputation: 115
there is not a computer near me now. Just a try:
crc = (crc << 8) ^ crctable[(unsigned char)(crc >> 8) ^ *c++];
Upvotes: 1