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View Code? Open in Web Editor NEWFastest crc32c algorithms for i686 and x86_64 including benchmarks
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knightku cwlbraa old101 elomkov shines77 ymarkovitch ixiaoi qwan-cohesity lordvampir1983 clayne terrillmoore yyolk pombredanne seesea1009 lightbitslabs xusenqi yygcodecrc32c's Issues
hanging submodule
you've got no .gitmodules file, and yet there's a gitlink for crc32c/crc32c/crc32c, which is fragile for anyone who might want to submodule in your lovely implementation...
Results Don't Agree with zlib
Although the crc32c results I'm seeing are consistent with the tests in this library, they do not agree with the crc32 results of other libraries, such as zlib:
#include <crc32c/crc32c.h>
#include <zlib.h>
unsigned long crc_zlib = crc32(0L, Z_NULL, 0);
std::string test_string = "hello-world";
uint32_t truth = 2983461467;
const auto test_string_chars = reinterpret_cast<const unsigned char*>(test_string.c_str());
crc_zlib = crc32(crc_zlib, (const unsigned char*)test_string_chars, test_string.length()); // this is zlib
uint32_t crc_c = crc32c::Crc32c(test_string); //
std::cout << "truth: " << truth << ", zlib: " << crc_zlib << ", crc32c: " << crc_c << std::endl;produces the output:
truth: 2983461467, zlib: 2983461467, crc32c: 4099351003
Calling the same with test_string = "The quick brown fox jumps over the lazy dog" produces the output:
truth: 576848900, zlib: 1095738169, crc32c: 576848900
You can see the short phrase "The quick brown fox..." produces the same crc as in your tests, but it does not agree with zlib. The zlib result on "hello-world" agrees with all of the sources listed here.
I thought perhaps there was a difference in what was being calculated, such as returning the signed 32-bit crc rather than unsigned, but it is indeed returning a unit32_t, so that wouldn't explain it.
This is a Google Cloud Compute instance with haswell Intel architecture. When I build the project, running ./crc32c_test shows all tests PASSED.
Do you have any guidance on what the discrepancy may be? Thanks!
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