Floating Point Precision in Bourne Shell

#!/bin/sh
# f_perc [-n precision] dividend [/] divisor [var_to_set]
#
# Calculate floating-point percentage for dividend within divisor. Default is
# to provide two significant figures (floating-point digits) unless given
# `-n precision' where precision is the number of desired sig-figs. An optional
# division-sign [/] may appear between the dividend and divisor.
#
# If var_to_set is missing or NULL, the result is printed to standard output.
# NB: This function does not round-up the last sig-fig (regardless).
#
f_perc()
{
        local OPTIND=1 OPTARG __flag __np=2
        while getopts n: __flag; do
                case "$__flag" in n) __np="$OPTARG" ;; esac
        done
        shift $(( $OPTIND - 1 ))
        local __dividend="$1" __divisor="$2" __var_to_set="$3"
        [ "$__divisor" = "/" ] && __divisor="$3" __var_to_set="$4"
        local __whole=0 __remainder=$(( $__dividend * 100 )) __n=1
        local __answer=$(( $__remainder / $__divisor ))
        [ $__np -gt 0 ] && __answer=$__answer.
        while [ $__n -le $__np ]; do
                __whole=$(( $__remainder / $__divisor ))
                __remainder=$(( $__remainder % $__divisor * 10 ))
                __answer=$__answer$(( $__remainder / $__divisor ))
                __n=$(( $__n + 1 ))
        done
        if [ "$__var_to_set" ]; then
                setvar "$__var_to_set" "$__answer%"
        else
                echo $__answer%
        fi
}
run=0 start=$( date +%s )
while [ $run -lt 100000 ]; do
        f_perc -n5 1 / 85 perc # 1.17647%
        run=$(( $run + 1 ))
done
stop=$( date +%s )
echo "$run runs in ~$(( $stop - $start ))s; perc=[$perc]"