[Chicken-users] timegm() considered harmful

[John Cowan]

Chicken 2.41 still won't build on Solaris because there is no timegm()
function there; it's a GNU extension, and Solaris doesn't have a GNU libc.
A fallback implementation, currently used only on Cygwin, does appear
in posixunix.scm, but it doesn't work on Solaris 8 either because it
uses setenv() and unsetenv(), which do not exist there -- they were not
added to Posix until a later revision.  I see two possibilities:

1) Remove timegm() references altogether, on the ground that the
function simply isn't Posix and doesn't belong in a Posix library.
The GNU C library documentation calls it "rarely available", that is,
unavailable except where GNU libc is the system libc.

2) Use a potentially inaccurate implementation like this:

        int offset = gmtime() - localtime();
        time_t result = mktime(blah, blah, blah ...);
        return result + offset;

The danger here is that the gmtime() and localtime() calls could
occur in different seconds, thus causing the difference to be
off by 1 second most of the time, or by a much larger number
at a DST transition or change of time zone.

-- 
Don't be so humble.  You're not that great.             John Cowan
        --Golda Meir                                    address@hidden