I would advise you to look at a standard hashing algorithm (like sha1,sha2 or md5)
If you still want to do it yourself:
$string = "This is a string to split and sum";
@chars = split(//,$string);
$sum = 0;
for(@chars)
{
#ord returns the numeric value of the char
printf"char = %s:bin = %8b:dec = %d\n",$_,ord,ord;
$sum+=ord;
}
print "sum = $sum\n";
#OUTPUT
#char = T:bin = 1010100:dec = 84
#char = h:bin = 1101000:dec = 104
#char = i:bin = 1101001:dec = 105
#char = s:bin = 1110011:dec = 115
#char = :bin = 100000:dec = 32
#char = i:bin = 1101001:dec = 105
#char = s:bin = 1110011:dec = 115
#char = :bin = 100000:dec = 32
#char = a:bin = 1100001:dec = 97
#char = :bin = 100000:dec = 32
#char = s:bin = 1110011:dec = 115
#char = t:bin = 1110100:dec = 116
#char = r:bin = 1110010:dec = 114
#char = i:bin = 1101001:dec = 105
#char = n:bin = 1101110:dec = 110
#char = g:bin = 1100111:dec = 103
#char = :bin = 100000:dec = 32
#char = t:bin = 1110100:dec = 116
#char = o:bin = 1101111:dec = 111
#char = :bin = 100000:dec = 32
#char = s:bin = 1110011:dec = 115
#char = p:bin = 1110000:dec = 112
#char = l:bin = 1101100:dec = 108
#char = i:bin = 1101001:dec = 105
#char = t:bin = 1110100:dec = 116
#char = :bin = 100000:dec = 32
#char = a:bin = 1100001:dec = 97
#char = n:bin = 1101110:dec = 110
#char = d:bin = 1100100:dec = 100
#char = :bin = 100000:dec = 32
#char = s:bin = 1110011:dec = 115
#char = u:bin = 1110101:dec = 117
#char = m:bin = 1101101:dec = 109
#sum = 3043