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# The following is Public Domain / Creative Commons CC0 from
# http://billauer.co.il/blog/2011/05/perl-crc32-crc-xs-module/
sub mycrc32 {
my ($input, $init_value, $polynomial) = @_;
$init_value = 0 unless (defined $init_value);
$polynomial = 0xedb88320 unless (defined $polynomial);
my @lookup_table;
for (my $i=0; $i<256; $i++) {
my $x = $i;
for (my $j=0; $j<8; $j++) {
if ($x & 1) {
$x = ($x >> 1) ^ $polynomial;
} else {
$x = $x >> 1;
}
}
push @lookup_table, $x;
}
my $crc = $init_value ^ 0xffffffff;
foreach my $x (unpack ('C*', $input)) {
$crc = (($crc >> 8) & 0xffffff) ^ $lookup_table[ ($crc ^ $x) & 0xff ];
}
$crc = $crc ^ 0xffffffff;
return $crc;
}
# Fix the checksum of an InnoDB tablespace page.
# Inputs:
# $page A bytestring with the page data.
# $full_crc32 Checksum type, see get_full_crc32() in innodb-util.pl
# Returns: the modified page as a bytestring.
sub fix_page_crc {
my ($page, $full_crc32)= @_;
my $ps= length($page);
my $polynomial = 0x82f63b78; # CRC-32C
if ($full_crc32) {
my $ck = mycrc32(substr($page, 0, $ps - 4), 0, $polynomial);
substr($page, $ps - 4, 4) = pack("N", $ck);
} else {
my $ck= pack("N",
mycrc32(substr($page, 4, 22), 0, $polynomial) ^
mycrc32(substr($page, 38, $ps - 38 - 8), 0, $polynomial));
substr($page, 0, 4)= $ck;
substr($page, $ps-8, 4)= $ck;
}
return $page;
}
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