Semantics of "seteuid(uid)" vs. "setreuid(-1,uid)"

[StefanEßer]

Any reason, that there is a difference in semantics between:

	seteuid(id)	vs.	setreuid(-1, id)	???

The tests performed on the arguments are different (assuming a
fixed arg of -1 for ruid) in that seteuid does not support the
case of (euid == cr_uid):

seteuid(euid):

	euid != oldcred->cr_ruid &&
	euid != oldcred->cr_svuid

setreuid(-1, euid):

	euid != oldcred->cr_uid &&
	euid != oldcred->cr_ruid &&
	euid != oldcred->cr_svuid

So seteuid() may fail in cases where setreuid() with a first argument
of -1 succeeds. The test obviously corresponds to POSIX appendix B.4.2.2
as mentioned in the comment in setuid().

Is the difference between seteuid() and setreuid() deliberate ?

I'm asking because I have received a bug report for a port, and it appears
that seteuid() on other systems is indeed equivalent to our setreuid(-1,).

Regards, STefan