What tricks used in readlink to make it faster than realpath bash loadable?

[Peng Yu]

Hi,

`readlink` is faster than `realpath` for a large number of input
arguments. Note that the former starts slower than the latter. What
tricks is used in readlink to make it faster? Thanks.

https://github.com/bminor/bash/blob/master/examples/loadables/realpath.c

bash> builtin enable -f
~/Downloads/bash-4.4/examples/loadables/realpath realpath
bash> type realpath
realpath is a shell builtin
bash> type readlink
readlink is /usr/local/opt/coreutils/libexec/gnubin/readlink
bash> readlink -e . > /dev/null

real    0m0.014s
user    0m0.003s
sys    0m0.006s
bash> realpath . > /dev/null

real    0m0.003s
user    0m0.001s
sys    0m0.002s
bash> readlink -e $(printf '. %.0s' {1..10000}) > /dev/null

real    0m0.200s
user    0m0.078s
sys    0m0.121s
bash> realpath $(printf '. %.0s' {1..10000}) > /dev/null

real    0m0.211s
user    0m0.105s
sys    0m0.103s

-- 
Regards,
Peng