CVS commit: src/lib/libc/time

["Robert Elz" <kre%netbsd.org@localhost>]

Module Name:    src
Committed By:   kre
Date:           Sat Nov  5 23:09:37 UTC 2016

Modified Files:
        src/lib/libc/time: zic.c

Log Message:
Actually, this problem won't be reported upstream, their code is
just ...

        ptrdiff_t nitems_max = PTRDIFF_MAX - WORK_AROUND_QTBUG_53071;
        ptrdiff_t amax = nitems_max < SIZE_MAX ? nitems_max : SIZE_MAX;

which is just fine if you think about it a little,   Unfortunately,
in our zealous effort to never leave a ggc warning unused, and to
treat all of the warnings as fatal errors, that code falls foul of the
"you must not compare an unsigned value with a signed value" warning.

nitems_max is a (signed) largish positive integer (obviously, by
inspection).  If it is less than SIZE_MAX then amax is just nitems_max.
In the unlikely case that size_t has less bits than ptrdiff_t so
SIZE_MAX is smaller, amax is limited to SIZE_MAX (which in that case
is known to fit in the ptrdiff_t and to remain positive).

To pacify gcc (and the way the build system uses it), casts are
required.   Unfortunately the cast that was installed here was to
convert SIZE_MAX to a ptrdiff_t.  Unfortunately when ptrdiff_t has
the same number of bits (or less) as size_t (ie: the common case)
but is signed, (ptrdiff_t)SIZE_MAX is just a fancy way of writing -1.

Rearrange the casting in a way that keeps the original intent
of the code for us (it is actyaly now incorrect if size_t has less
bits than a ptrdiff_t) and keeps gcc happy, all at the same time.

What a mess.


To generate a diff of this commit:
cvs rdiff -u -r1.66 -r1.67 src/lib/libc/time/zic.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.