DP=3
MOD=1000

function ftofix {       # ftofix OUTPUTNAME "3.14"
        _VAR="$1"
        _OLDIFS="$IFS"
        IFS="."
                set -- $2 # Set $1, $2, etc, splitting on "."
        IFS="$_OLDIFS"
        local FRAC=$2
        local _N=$1

        [[ "${_N}" =  "0" ]] && _N=""
        [[ "${_N}" = "-0" ]] && _N="-"

        for((X=0; X<DP; X++))
        do
                D="${FRAC:$X:1}"
                [[ -z "$D" ]] && D="0"
                _N="${_N}$D" # Prepend digits to N
        done
        read $_VAR <<EOF
${_N}
EOF

}

function fixtof {
        _VAR="$1"
        _N="$2"
        _SIGN=""
        ((_N<0)) && _SIGN="-" && ((_N=-_N))
        _S=`printf "%s%d.%0${DP}d" "${_SIGN}" $((_N/MOD)) $((_N%MOD))`
        read $_VAR <<EOF
$_S
EOF
}

AA="3.14159"
BB="-2.0"

ftofix A $AA
ftofix B $BB

# Multiplcation
fixtof CC $(((A*B)/MOD))
echo "$AA * $BB = $CC"

# Division
fixtof DD $(( (A*MOD)/B ))
echo "$AA / $BB = $DD"

# Addition and Subtraction
fixtof EE $(( B - A ))
echo "$BB - $AA = $EE"
fixtof FF $(( A - B ))
echo "$AA - $BB = $FF"
fixtof GG $(( A + B ))
echo "$AA + $BB = $GG"

3.14159 * -2.0 = -6.282
3.14159 / -2.0 = -1.570
-2.0 - 3.14159 = -5.141
3.14159 - -2.0 = 5.141
3.14159 + -2.0 = 1.141