...reserved for each element in the bit vector.

You were wanting 64 bits, so each is one bit wide. This is 32-bit perl:

$ perl -e 'vec( $foo, 63, 1) = 1; print unpack( "b64",$foo),$/'
0000000000000000000000000000000000000000000000000000000000000001
[download]

or, if you prefer your high order bits printed on the left,

$ perl -e 'vec( $foo, 63, 1) = 1; print scalar reverse(unpack "b64",$f
+oo),$/'
1000000000000000000000000000000000000000000000000000000000000000
[download]

The bitwise operators work on vec() strings

After Compline,
Zaxo