#!/bin/sh
# $1 * $2
# count the total decimal places
countd() {
  [ -z "${1##*.*}" ] && {
    m="$1"; n=${2:-0}; while [ "$m" ]; do
      : $((n+=1))
      next="${m%?}"
      [ "${m#$next}" = "." ] && {
        break
      } || {
        m="$next"
      }
    done
  } || n=1
  echo "$n"
}
[ -z "${1##*.*}" -o -z "${2##*.*}" ] || { # if not floats
  echo "$(($1*$2))"
  exit 0
}
dn=$(countd "$2" $(countd "$1")); [ "$dn" -gt 2 ] && : $((dn-=2)) # decimal count
#echo "$dn | $(countd $1) -- $(countd $2)"
# remove all decimal places
if [ ! -z "${1##*.*}" ]; then # if $1 is not float
  set -- "$1" "${2%.*}${2#*.}"
elif [ ! -z "${2##*.*}" ]; then
  set -- "${1%.*}${1#*.}" "$2"
else
  set -- "${1%.*}${1#*.}" "${2%.*}${2#*.}"
fi
#echo "$1 * $2"
o="$(($1*$2))"
# add back decimal point using $dn
n=0; m="$o"; [ "$dn" -gt 0 ] && while [ "$m" ]; do
  next="${m%?}"
  : $((n+=1))
  [ "$n" -eq "$dn" ] && o="$next.${o#${m%?}}"
  m="$next"
done
echo "$o"