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From: Francesco Potorti` <pot@gnu.org>
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Subject: suspect error in regex.c
Date: Thu, 05 Sep 2002 17:32:45 +0200
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I don't know how regex.c works, but this looks strange to me (I
discovered it because of a warning issued by MSVC on a report I got
about etags, which uses regex.c):

== src/regex.c ==

1837:typedef unsigned regnum_t;

in regex_compile:
2245:  regnum_t regnum = 0;
2847: 		COMPILE_STACK_TOP.regnum = shy ? -regnum : regnum;

Notice that an unsigned value is negated, then assigned to an unsigned
field.

later in regex_compile:
2897:		regnum_t this_group_regnum;
2906:		this_group_regnum = COMPILE_STACK_TOP.regnum;
2914:		if (this_group_regnum <= MAX_REGNUM && this_group_regnum > 0)

That is, the same unsigned value is compared against MAX_REGNUM and 0.
In principle, the code could be correct, but it does sound strange to me
that such a particular programming practice is not even commented.
Looks suspiciously like a bug to me.