sub fun {
# (explained : reduce the numbers to their base2 (binary)
# representation.  we always care about the
# lowest four bits ($n & 0x1111 is $n & 15).  If the ord of
# the number is in the A-Z range the 7th bit will be set
# ($n >> 6) will be true.  In this case, also include the
# 6th bit in the number ($n & 31) instead of ($n & 15).
# Since A-Z starts at ten, add 9 as well)
    #        1         2         3         4         5         6
    #23456789012345678901234567890123456789012345678901234567890
    $n=ord(pop);$a=($n>>6)?(($n&31)+9):($n&15);
    # same thing, but obfu
  # $n=ord(pop);$a=($n&(1<<(4+($n>>6)))-1)+($n>>6&&9);
}