Hurcan Solter wrote on 07/09/2015 10:21 PM:

So,you are initializing the crc with a different value(result from previous loop) and expecting the same result?

I don't think so, but if you know how to use it correctly let me know pls. I just wonder why the lib author made such a simple thing so complicated. The program even gives different results with each run; so there must definitely be a bug in the crc library.

On Thu, Jul 9, 2015 at 8:27 PM, U.Mutlu wrote:

...

/* boost-crc-bug-demo.cpp

Written by U.Mutlu on 2015-07-09-Th

Compile: g++ -O2 -Wall -std=gnu++11 boost-crc-bug-demo.cpp

Run: ./a.out

Output: crc("The quick brown fox jumps over the lazy dog")=414fa339 crc("The quick brown fox ")=88b075e2 crc("The quick brown fox jumps over the lazy dog")=4ac56d0f ERROR

See also: http://www.boost.org/doc/libs/1_58_0/libs/crc/crc.html#usage

Conclusion: It doesn't do what it should and also advertises; ie. there's a bug

*/

#include #include #include <iostream>

int main() { uint32_t expected;

{ const std::string sTxt = "The quick brown fox jumps over the lazy dog"; boost::crc_optimal<32, 0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true, true> crc; crc.process_bytes(sTxt.data(), sTxt.size()); std::cout << "crc(\"" << sTxt << "\")=" << std::hex << crc.checksum() << std::endl;

// save the result for the following test expected = crc.checksum(); }

// test: doing the same as above, but now in 2 steps, ie. chunk- or blockwise: std::string sTxt; uint32_t result = 0xFFFFFFFF; for (size_t i = 0; i <= 1; ++i) { sTxt += !i ? "The quick brown fox " : "jumps over the lazy dog";

// using the special ctor for initial remainder stored in "result" boost::crc_optimal<32, 0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true, true> crc(result); crc.process_bytes(sTxt.data(), sTxt.size()); std::cout << "crc(\"" << sTxt << "\")=" << std::hex << crc.checksum() << std::endl;

result = crc.checksum(); }

// eval: const std::string sRes = result == expected ? "SUCCESS" : "ERROR"; std::cout << sRes << std::endl;

return 0; }

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Bjorn Reese wrote on 07/09/2015 11:45 PM:

On 07/09/2015 07:27 PM, U.Mutlu wrote:

...

// test: doing the same as above, but now in 2 steps, ie. chunk- or blockwise: std::string sTxt; uint32_t result = 0xFFFFFFFF; for (size_t i = 0; i <= 1; ++i) { sTxt += !i ? "The quick brown fox " : "jumps over the lazy dog";

Bug 1: Do not append to the string.

...

// using the special ctor for initial remainder stored in "result" boost::crc_optimal<32, 0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true, true> crc(result);

Bug 2: Do not pass checksum() as the initial remainder, but rather get_interrim_remainder().

Thx, now it works.