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New zic -b option to shrink data and test y2038
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* Makefile (ZFLAGS): Mention -b in comment.
* NEWS: Mention this.
* zic.c (usage): Mention -b.
(bloat): New static var.
(want_bloat): New static function.
(main): Parse new -b option.
(writezone): In slim output, suppress QTBUG-53071 workaround,
pre-2011 bug workaround, all-zero isstdcnt and isutcnt indicators,
and 32-bit data (except for header and the single type that RFC
8536 requires).
(outzone): In slim output, suppress redundant transitions back to
1900 or forward through 2038, and suppress redundant transitions
just before the TZ string takes over.
* zic.8: Document -b.  Sort options alphabetically.
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@eggert
eggert committed Jun 13, 2019
1 parent b8b8941 commit 7879a3f
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12 changes: 10 additions & 2 deletions Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -362,9 +362,17 @@ LEAPSECONDS=
zic= ./zic
ZIC= $(zic) $(ZFLAGS)

# To shrink the size of installed TZif files,
# Append "-b fat" to install larger TZif files that work around
# incompatiblities and bugs in some TZif readers, notably readers that
# mishandle 64-bit data in TZif files. Append "-b slim" to install
# smaller TZif files that test for these year-2038 bugs. If no -b
# option is given, the current default is "-b fat", but this is
# intended to change as buggy readers often mishandle timestamps
# after 2038 anyway.
#
# To shrink the size of installed TZif files even further,
# append "-r @N" to omit data before N-seconds-after-the-Epoch.
# See the zic man page for more about -r.
# See the zic man page for more about -b and -r.
ZFLAGS=

# How to use zic to install TZif files.
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14 changes: 14 additions & 0 deletions NEWS
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,20 @@ Unreleased, experimental changes

Changes to code

zic's new -b option supports a way to control data bloat and to
test for year-2038 bugs in software that reads TZif files.
'zic -b fat' and 'zic -b slim' generate larger and smaller output;
for example, changing from fat to slim shrinks the Europe/London
file from 3648 to 1625 bytes, saving about 55%. Fat and slim
files represent the same time data and use the same TZif format as
documented in tzfile(5) and in Internet RFC 8536. Fat format
attempts to work around bugs or incompatibilities on older
software that reads TZif files, notably software that mishandles
64-bit TZif data. Slim format is more efficient and tests for
these bugs. Currently zic defaults to fat format, although this
is intended to change in future zic versions, as the buggy
software typically mishandles post-2038 timestamps anyway.

zic no longer treats a set of rules ending in 2037 specially.
Previously, zic assumed that such a ruleset meant that future
timestamps could not be predicted, and therefore omitted a
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47 changes: 38 additions & 9 deletions zic.8
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,32 @@ Output version information and exit.
.B \*-\*-help
Output short usage message and exit.
.TP
.BI "\*-b " bloat
Output backward-compatibility data as specified by
.IR bloat .
If
.I bloat
is
.BR fat ,
generate additional data entries that work around potential bugs or
incompatibilities in older software, such as software that mishandles
the 64-bit generated data.
If
.I bloat
is
.BR slim ,
keep the output files small; this can help check for the bugs
and incompatibilities.
Although the default is currently
.BR fat ,
this is intended to change in future
.B zic
versions, as software that mishandles the 64-bit data typically
mishandles timestamps after the year 2038 anyway.
Also see the
.B \*-r
option for another way to shrink output size.
.TP
.BI "\*-d " directory
Create time conversion information files in the named directory rather than
in the standard directory named below.
Expand All @@ -59,6 +85,11 @@ will act as if the input contained a link line of the form
.ti +.5i
Link \fItimezone\fP localtime
.TP
.BI "\*-L " leapsecondfilename
Read leap second information from the file with the given name.
If this option is not used,
no leap second information appears in output files.
.TP
.BI "\*-p " timezone
Use
.IR timezone 's
Expand All @@ -70,15 +101,6 @@ will act as if the input contained a link line of the form
.ti +.5i
Link \fItimezone\fP posixrules
.TP
.BI "\*-t " file
When creating local time information, put the configuration link in
the named file rather than in the standard location.
.TP
.BI "\*-L " leapsecondfilename
Read leap second information from the file with the given name.
If this option is not used,
no leap second information appears in output files.
.TP
.BR "\*-r " "[\fB@\fP\fIlo\fP][\fB/@\fP\fIhi\fP]"
Reduce the size of output files by limiting their applicability
to timestamps in the range from
Expand All @@ -102,6 +124,13 @@ On platforms with GNU
.BR date ,
.q "zic \-r @$(date +%s)"
omits data intended for past timestamps.
Also see the
.B "\*-b slim"
option for another way to shrink output size.
.TP
.BI "\*-t " file
When creating local time information, put the configuration link in
the named file rather than in the standard location.
.TP
.B \*-v
Be more verbose, and complain about the following situations:
Expand Down
89 changes: 71 additions & 18 deletions zic.c
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Original file line number Diff line number Diff line change
Expand Up @@ -574,8 +574,9 @@ usage(FILE *stream, int status)
{
fprintf(stream,
_("%s: usage is %s [ --version ] [ --help ] [ -v ] \\\n"
"\t[ -l localtime ] [ -p posixrules ] [ -d directory ] \\\n"
"\t[ -t localtime-link ] [ -L leapseconds ] [ -r '[@lo][/@hi]' ] \\\n"
"\t[ -b {slim|fat} ] [ -d directory ] [ -l localtime ]"
" [ -L leapseconds ] \\\n"
"\t[ -p posixrules ] [ -r '[@lo][/@hi]' ] [ -t localtime-link ] \\\n"
"\t[ filename ... ]\n\n"
"Report bugs to %s.\n"),
progname, progname, REPORT_BUGS_TO);
Expand Down Expand Up @@ -650,6 +651,17 @@ static const char * leapsec;
static const char * tzdefault;
static const char * yitcommand;

/* -1 if the TZif output file should be slim, 0 if default, 1 if the
output should be fat for backward compatibility. Currently the
default is fat, although this may change. */
static int bloat;

static bool
want_bloat(void)
{
return 0 <= bloat;
}

int
main(int argc, char **argv)
{
Expand Down Expand Up @@ -681,10 +693,22 @@ main(int argc, char **argv)
} else if (strcmp(argv[k], "--help") == 0) {
usage(stdout, EXIT_SUCCESS);
}
while ((c = getopt(argc, argv, "d:l:L:p:r:st:vy:")) != EOF && c != -1)
while ((c = getopt(argc, argv, "b:d:l:L:p:r:st:vy:")) != EOF && c != -1)
switch (c) {
default:
usage(stderr, EXIT_FAILURE);
case 'b':
if (strcmp(optarg, "slim") == 0) {
if (0 < bloat)
error(_("incompatible -b options"));
bloat = -1;
} else if (strcmp(optarg, "fat") == 0) {
if (bloat < 0)
error(_("incompatible -b options"));
bloat = 1;
} else
error(_("invalid option: -b '%s'"), optarg);
break;
case 'd':
if (directory == NULL)
directory = optarg;
Expand Down Expand Up @@ -1921,7 +1945,7 @@ writezone(const char *const name, const char *const string, char version,
seconds, as the idea is to insert a transition just before
32-bit time_t rolls around, and this occurs at a slightly
different moment if transitions are leap-second corrected. */
if (WORK_AROUND_QTBUG_53071 && timecnt != 0
if (WORK_AROUND_QTBUG_53071 && timecnt != 0 && want_bloat()
&& ats[timecnt - 1] < y2038_boundary - 1 && strchr(string, '<')) {
ats[timecnt] = y2038_boundary - 1;
types[timecnt] = types[timecnt - 1];
Expand Down Expand Up @@ -1970,7 +1994,7 @@ writezone(const char *const name, const char *const string, char version,
int old0;
char omittype[TZ_MAX_TYPES];
int typemap[TZ_MAX_TYPES];
register int thistypecnt;
int thistypecnt, stdcnt, utcnt;
char thischars[TZ_MAX_CHARS];
int thischarcnt;
bool toomanytimes;
Expand Down Expand Up @@ -2053,7 +2077,7 @@ writezone(const char *const name, const char *const string, char version,
** (to help get global "altzone" and "timezone" variables
** set correctly).
*/
{
if (want_bloat()) {
register int mrudst, mrustd, hidst, histd, type;

hidst = histd = mrudst = mrustd = -1;
Expand Down Expand Up @@ -2100,12 +2124,16 @@ writezone(const char *const name, const char *const string, char version,

for (i = 0; i < sizeof indmap / sizeof indmap[0]; ++i)
indmap[i] = -1;
thischarcnt = 0;
thischarcnt = stdcnt = utcnt = 0;
for (i = old0; i < typecnt; i++) {
register char * thisabbr;

if (omittype[i])
continue;
if (ttisstds[i])
stdcnt = thistypecnt;
if (ttisgmts[i])
utcnt = thistypecnt;
if (indmap[abbrinds[i]] >= 0)
continue;
thisabbr = &chars[abbrinds[i]];
Expand All @@ -2118,12 +2146,18 @@ writezone(const char *const name, const char *const string, char version,
}
indmap[abbrinds[i]] = j;
}
if (pass == 1 && !want_bloat()) {
utcnt = stdcnt = thisleapcnt = 0;
thistimecnt = - locut - hicut;
thistypecnt = thischarcnt = 1;
thistimelim = thistimei;
}
#define DO(field) fwrite(tzh.field, sizeof tzh.field, 1, fp)
tzh = tzh0;
memcpy(tzh.tzh_magic, TZ_MAGIC, sizeof tzh.tzh_magic);
tzh.tzh_version[0] = version;
convert(thistypecnt, tzh.tzh_ttisgmtcnt);
convert(thistypecnt, tzh.tzh_ttisstdcnt);
convert(utcnt, tzh.tzh_ttisgmtcnt);
convert(stdcnt, tzh.tzh_ttisstdcnt);
convert(thisleapcnt, tzh.tzh_leapcnt);
convert(locut + thistimecnt + hicut, tzh.tzh_timecnt);
convert(thistypecnt, tzh.tzh_typecnt);
Expand All @@ -2138,6 +2172,15 @@ writezone(const char *const name, const char *const string, char version,
DO(tzh_typecnt);
DO(tzh_charcnt);
#undef DO
if (pass == 1 && !want_bloat()) {
/* Output a minimal data block with just one time type. */
puttzcode(0, fp); /* utoff */
putc(0, fp); /* dst */
putc(0, fp); /* index of abbreviation */
putc(0, fp); /* empty-string abbreviation */
continue;
}

/* Output a LO_TIME transition if needed; see limitrange.
But do not go below the minimum representable value
for this pass. */
Expand Down Expand Up @@ -2193,10 +2236,12 @@ writezone(const char *const name, const char *const string, char version,
puttzcodepass(todo, fp, pass);
puttzcode(corr[i], fp);
}
for (i = old0; i < typecnt; i++)
if (stdcnt != 0)
for (i = old0; i < typecnt; i++)
if (!omittype[i])
putc(ttisstds[i], fp);
for (i = old0; i < typecnt; i++)
if (utcnt != 0)
for (i = old0; i < typecnt; i++)
if (!omittype[i])
putc(ttisgmts[i], fp);
swaptypes(old0, thisdefaulttype);
Expand Down Expand Up @@ -2643,16 +2688,18 @@ outzone(const struct zone *zpfirst, ptrdiff_t zonecount)
max_year = min_year + years_of_observations;
}
}
/*
** For the benefit of older systems,
** generate data from 1900 through 2038.
*/
if (min_year > 1900)
min_year = 1900;
max_year0 = max_year;
if (max_year < 2038)
if (want_bloat()) {
/* For the benefit of older systems,
generate data from 1900 through 2038. */
if (min_year > 1900)
min_year = 1900;
if (max_year < 2038)
max_year = 2038;
}

for (i = 0; i < zonecount; ++i) {
struct rule *prevrp = NULL;
/*
** A guess that may well be corrected later.
*/
Expand Down Expand Up @@ -2788,6 +2835,11 @@ outzone(const struct zone *zpfirst, ptrdiff_t zonecount)
doabbr(ab, zp, rp->r_abbrvar,
rp->r_isdst, rp->r_stdoff, false);
offset = oadd(zp->z_gmtoff, rp->r_stdoff);
if (!want_bloat() && !useuntil && !do_extend
&& prevrp
&& rp->r_hiyear == ZIC_MAX
&& prevrp->r_hiyear == ZIC_MAX)
break;
type = addtype(offset, ab, rp->r_isdst,
rp->r_todisstd, rp->r_todisgmt);
if (defaulttype < 0 && !rp->r_isdst)
Expand All @@ -2797,6 +2849,7 @@ outzone(const struct zone *zpfirst, ptrdiff_t zonecount)
&& ktime < attypes[lastatmax].at))
lastatmax = timecnt;
addtt(ktime, type);
prevrp = rp;
}
}
if (usestart) {
Expand Down

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