adler32

adler32($buffer [, $adler]): the Adler-32 checksum of $buffer. Pass the previous result as $adler to continue a running checksum; without it, or with undef, the checksum starts afresh. $buffer may be a scalar reference. Exported by default.

my $a = adler32("hello, ");
$a = adler32("world", $a);        # same as adler32("hello, world")

A string with characters above 255 that cannot be downgraded dies “Wide character in Compress::Raw::Zlib::adler32”.