#! /bin/sh

# pow2 -- computes powers of 2 
# $Id: pow2,v 1.3 1998/07/09 02:40:50 cdua Exp cdua $
# Carlos Duarte, 960719/971116

#trap -- 'rm -f /tmp/xpto' EXIT SIGINT

USAGE="\
usage: $0 [-h] first last 
   or: $0      value

  -h      this help

    first form, computes powers in range [first, last]
    second, only computes for given value
"

while : ; do
	case x"$1" in 
	x-h)	echo "$USAGE"; exit 1 ;;
	x--)	shift; break ;;
	x-?)	echo "invalid option -- `echo $1|cut -c2-`"
		echo "$USAGE"; exit 1 ;;
	*)	break ;;
	esac
	shift
done

case $# in 
1)	last=$1
	first=$1
	;;
2)	first=$1
	last=$2
	;;
*)	echo "$USAGE"; 
	exit 1;
	;;
esac

: ${first=1} ${last=20}

bc << eof
pow = 2 ^ $first
for ( i = $first; i <= $last; i += 1 ) {
	print "2^", i, " = ", pow, "\n"
	pow = pow * 2
}
quit
eof

exit