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=head1 NAME |
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String::CRC32C - Castagnoli CRC |
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=head1 SYNOPSIS |
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use String::CRC32C; # does not export anything by default |
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use String::CRC32C 'crc32c'; |
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$crc = crc32 "some string"; |
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$crc = crc32 "some string", $initvalue; |
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=head1 DESCRIPTION |
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This module calculates the Castagnoli CRC32 variant (polynomial 0x11EDC6F41). |
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It is used by iSCSI, SCTP, BTRFS, ext4, leveldb, x86 CPUs and others. |
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This module uses an optimized implementation for SSE 4.2 targets (GCC |
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and compatible supported, SSE 4.2 must be enabled in your Perl) and the |
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SlicingBy8 algorithm for anything else. |
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=cut |
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package String::CRC32C; |
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our $IMPL; |
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BEGIN { |
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$VERSION = '1.0'; |
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@ISA = qw(Exporter); |
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@EXPORT_OK = qw(crc32c); |
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require XSLoader; |
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XSLoader::load String::CRC32C, $VERSION; |
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} |
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use Exporter qw(import); |
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=over |
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=item $crc32c = crc32c $string[, $initvalue] |
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Calculates the CRC32C value of the given C<$string> and returns it as a 32 |
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bit unsigned integer. |
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To get the common hex form, use one of: |
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sprintf "%08x", crc32c $string |
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unpack "H*", pack "L>", crc32c $string |
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A seed/initial crc value can be given as second argument. Note that both |
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the initial value and the result value are inverted (pre-inversion and |
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post-inversion), e.g. a common init value of C<-1> from other descriptions |
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needs to be given as C<0> (or C<~-1>). |
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This allows easy chaining, e.g. |
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(crc32c "abcdefghi") eq (crc32 "ghi", crc32 "def", crc32 "abc") |
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=item $String::CRC32C::IMPL |
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Contains a string indicating the implementation that will be used. Currently either C<SlicingBy8> |
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for the portable implementation or C<IntelCSSE42> for the SSE 4.2 optimized intel version. |
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=back |
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=head1 PERLMULTICORE SUPPORT |
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This module supports the perl multicore specification |
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(L<http://perlmulticore.schmorp.de/>): the C<crc32c> function will |
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relinquish the current thread for string lengths larger than 64k (the |
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break-even point on my machine is around 128k), so multiprocessing makes |
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only sense for very long blocks. |
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=head1 AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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CRC32C code by various sources, ported from |
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https://github.com/htot/crc32c, see sources for details. |
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=cut |
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