Ultra-fast internal which replacement for sh(1)

#!/bin/sh
: ${STRESS=10000}
SUCCESS=0
FAILURE=1
f_which()
{
    local __name="$1" __var_to_set="$2"
    case "$__name" in */*|'') return $FAILURE; esac
    if [ "$__var_to_set" ]; then
        # Do this without a sub-shell to keep things fast
            local __p IFS=":"
            for __p in $PATH; do
                    local __exec="$__p/$__name"
                    [ -f "$__exec" -a -x "$__exec" ] &&
                setvar "$__var_to_set" "$__exec" &&
                return $SUCCESS
            done
        else
        # Take a short-cut through the `hash' built-in
        type "$__name" > /dev/null 2>&1 &&
            hash -v "$__name" 2> /dev/null
    fi
}
if [ $# -ge 2 ]; then
    if [ ! "$STRESS" ]; then
        f_which "$1" "$2"
        retval=$?
        eval echo \"\$2=[\$$2]\"
        exit $retval
    else
        echo -n "Stressing f_which... "
        n=0
        start_epoch=$( date +%s )
        while [ $n -lt $STRESS ]; do
            f_which "$1" "$2"
            n=$(( $n + 1 ))
        done
        end_epoch=$( date +%s )
        echo "$(( $end_epoch - $start_epoch )) seconds ($STRESS runs)"

        echo -n "Stressing which... "
        n=0
        start_epoch=$( date +%s )
        while [ $n -lt $STRESS ]; do
            name=$( which "$1" )
            n=$(( $n + 1 ))
        done
        end_epoch=$( date +%s )
        echo "$(( $end_epoch - $start_epoch )) seconds ($STRESS runs)"
    fi
else
    if [ ! "$STRESS" ]; then
        f_which "$1"
        exit $?
    else
        echo -n "Stressing f_which... "
        n=0
        start_epoch=$( date +%s )
        while [ $n -lt $STRESS ]; do
            f_which "$1" > /dev/null
            n=$(( $n + 1 ))
        done
        end_epoch=$( date +%s )
        echo "$(( $end_epoch - $start_epoch )) seconds ($STRESS runs)"

        echo -n "Stressing which... "
        n=0
        start_epoch=$( date +%s )
        while [ $n -lt $STRESS ]; do
            which "$1" > /dev/null
            n=$(( $n + 1 ))
        done
        end_epoch=$( date +%s )
        echo "$(( $end_epoch - $start_epoch )) seconds ($STRESS runs)"
    fi
fi