HelenOS sources

root/uspace/lib/c/test/

[..]
adt/ capa.c casting.c double_to_str.c fibril/
getopt.c gsort.c ieee_double.c imath.c inttypes.c
io/ loc.c main.c mem.c perf.c
perm.c qsort.c sprintf.c stdio.c stdio/
stdlib.c str.c string.c strtol.c uuid.c
[..]
HelenOS homepage, sources at GitHub