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RobTillaart / CRC

CRC library for Arduino
MIT License
79 stars 17 forks source link

different crc32 result from crccalc.com/ #15

Closed Brandonn-Etheve closed 2 years ago

Brandonn-Etheve commented 2 years ago

Running included crc32 example sketch on an arduino uno i get:

/home/brd/Arduino/libraries/CRC/examples/CRC32_test/CRC32_test.ino 89A1897F 89A1897F 89A1897F CDBAC17A 18

while https://crccalc.com/ with "123456789" input: ascii, output: hex, i get: 0xCBF43926

here the crccalc result link

What i'm missing?

RobTillaart commented 2 years ago

I'll have a look ...

Got the same results as you (so it is at least consistent) CRC32_test.ino 89A1897F 89A1897F 89A1897F CDBAC17A 18

These are the settings, these are NOT in the table at crccalc.com

void CRC32::reset()
{
  _polynome   = CRC32_DEFAULT_POLYNOME;  (== 0x04C11DB7)
  _startMask  = 0;
  _endMask    = 0;
  _crc        = 0;
  _reverseIn  = false;
  _reverseOut = false;
  _started    = false;
  _count      = 0;
}

Checking with - http://zorc.breitbandkatze.de/crc.html and values seems OK.

image

Think you missed the XOR with 0xFFFFFF at the end (in the crccalc table)

RobTillaart commented 2 years ago

CDBAC17A is the CRC-32 when adding the string 123456789 twice.

Brandonn-Etheve commented 2 years ago

Thanks for your time. since there was a comment in the example sketch : // Serial.println("Verified with - https://crccalc.com/\n"); i though that the default setting should match the output of that website.

Using: crc.setPolynome(0x04C11DB7); crc.setStartXOR(0xFFFFFFFF); crc.setEndXOR(0xFFFFFFFF); crc.setReverseIn(true); crc.setReverseOut(true);

the output is CBF43926 as expected. since many website use those setting (including https://crc32.online/ and other) maybe you should use it as default setting, or add the link to http://zorc.breitbandkatze.de/crc.html instead of https://crccalc.com in the sketch comment. Anyways issue solved.

RobTillaart commented 2 years ago

Good point to use at least a setting that is in the table. I'll make a note of it for a next release to improve the examples.

Might be useful to have a dump() function to print all settings at once. => easier to check them.

RobTillaart commented 2 years ago

FYI triggered by your question I created a 0.2.0 version