gistfile1.txt

$ ( for sh in ksh mksh zsh bash; do "$sh" /dev/fd/3; done ) 3<<\EOF
${ZSH_VERSION+'false'} || emulate ksh
${BASH_VERSION+shopt -s expand_aliases}
${KSH_VERSION+\:} alias integer=typeset
[[ ${!KSH_VERSION} == .sh.version ]] || alias .=

function f {
    ${1+'false'} || integer depth=$1 iter=$2
    if ((!depth--)); then
        integer i=$iter
        time while ((i--)); do :; done
    else
        . f
    fi
}

f 600 1000000
EOF


real    0m0.23s
user    0m0.23s
sys     0m0.00s
    0m3.86s real     0m3.86s user     0m0.00s system

real    0m10.780s
user    0m10.781s
sys     0m0.000s