s() { c=$1; while((c--)) ; do printf 'x' ; done }; s 2

while((1--))

s() { for i; do printf 'x' ; done }; s 2 3

> set -- 5
> echo $1
5
> set -- $(( $1-1 ))
> echo $1
4

s() { while (( $1 )); do echo 'x'; set -- $(( ${1}-1 )); done }

>time s 100000 > /dev/null
real    0m1.235s
user    0m1.196s
sys     0m0.040s

>time s 100000 > /dev/null
real    0m0.520s
user    0m0.496s
sys     0m0.024s

s1() { for i in $(eval echo {1..${1}}); do printf 'x'; done }

>time s1 100000 > /dev/null
real    0m0.453s
user    0m0.412s
sys     0m0.040s