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strptime %z: fix rounding, extend range to +/-9959 [BZ #16141] 

Topic: strptime supports a %z input field descriptor, which parses a
time zone offset from UTC time into the broken-out time field tm_gmtoff.

Problems:

1) In the current implementation, the minutes portion calculation is
correct only for minutes evenly divisible by 3. This is because the
minutes value is converted to decimal time, but inadequate precision
leads to rounding which calculates results that are too low for
some values.

For example, due to rounding, a +1159 offset string results in an
incorrect tm_gmtoff of 43128 (== 11 * 3600 + 58.8 * 60) seconds,
instead of 43140 (== 11 * 3600 + 59 * 60) seconds. In contrast,
a +1157 offset (minutes divisible by 3) does not cause the bug,
and results in a correct tm_gmtoff of 43020.

2) strptime's %z specifier will not parse time offsets less than
-1200 or greater than +1200, or if only hour digits are present, less
than -12 or greater than +12. It will return NULL for offsets outside
that range. These limits do not meet historical and modern use cases:

  * Present day exceeds the +1200 limit:
    - Pacific/Auckland (New Zealand) summer time is +1300.
    - Pacific/Kiritimati (Christmas Island) is +1400.
    - Pacific/Apia (Samoa) summer time is +1400.
  * Historical offsets exceeded +1500/-1500.
  * POSIX supports -2459 to +2559.
  * Offsets up to +/-9959 may occasionally be useful.
  * Paul Eggert's notes provide additional detail:
    - https://sourceware.org/ml/libc-alpha/2014-12/msg00068.html
    - https://sourceware.org/ml/libc-alpha/2014-12/msg00072.html

3) tst-strptime2, part of the 'make check' test suite, does not test
for the above problems.

Corrective actions:

1) In time/strptime_l.c, calculate the offset from the hour and
minute portions directly, without the rounding errors introduced by
decimal time.

2) Remove the +/-1200 range limit, permitting strptime to parse offsets
from -9959 through +9959.

3) Add zone offset values to time/tst-strptime2.c.

  * Test minutes evenly divisible by three (+1157) and not evenly
    divisible by three (+1158 and +1159).
  * Test offsets near the old and new range limits (-1201, -1330, -2459,
    -2500, -99, -9959, +1201, +1330, +1400, +1401, +2559, +2600, +99,
    and +9959)

The revised strptime passes all old and new tst-strptime2 tests.
This commit is contained in:
James Perkins 2015-08-17 13:48:38 -07:00 committed by Mike Frysinger
parent 315267abcd
commit cccc95f28a
4 changed files with 40 additions and 15 deletions
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14
ChangeLog
View File

@ -1,3 +1,17 @@
2015-08-28 James Perkins <james@loowit.net>
[BZ #16141]
* time/strptime_l.c (__strptime_internal): Fix %z minutes
calculation, removing incorrect decimal time rounding, so that
all minute values result in a valid seconds value.
* time/strptime_l.c (__strptime_internal): Extend %z time zone
offset range limits to UTC-99:59 through UTC+99:59 to parse
current and historical use cases.
* time/tst-strptime2.c (tests): Modify and add tests for the
strptime %z input field descriptor, specifically conversion of
minutes to seconds and validating an offset range of -9959 to
+9959.
2015-08-27 Adhemerval Zanella <adhemerval.zanella@linaro.org>
Dmitry V. Levin <ldv@altlinux.org>

8
NEWS
View File

@ -9,10 +9,10 @@ Version 2.23
* The following bugs are resolved with this release:
2898, 14341, 15786, 16517, 16519, 16520, 16734, 16973, 17787, 17905,
18084, 18086, 18240, 18265, 18370, 18421, 18480, 18525, 18610, 18618,
18647, 18661, 18674, 18681, 18778, 18781, 18787, 18789, 18790, 18795,
18796, 18820, 18823, 18824, 18863.
2898, 14341, 15786, 16141, 16517, 16519, 16520, 16734, 16973, 17787,
17905, 18084, 18086, 18240, 18265, 18370, 18421, 18480, 18525, 18610,
18618, 18647, 18661, 18674, 18681, 18778, 18781, 18787, 18789, 18790,
18795, 18796, 18820, 18823, 18824, 18863.
* The obsolete header <regexp.h> has been removed. Programs that require
this header must be updated to use <regex.h> instead.

12
time/strptime_l.c
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@ -770,16 +770,10 @@ __strptime_internal (rp, fmt, tmp, statep LOCALE_PARAM)
else if (n != 4)
/* Only two or four digits recognized. */
return NULL;
else
{
/* We have to convert the minutes into decimal. */
if (val % 100 >= 60)
return NULL;
val = (val / 100) * 100 + ((val % 100) * 50) / 30;
}
if (val > 1200)
else if (val % 100 >= 60)
/* Minutes valid range is 0 through 59. */
return NULL;
tm->tm_gmtoff = (val * 3600) / 100;
tm->tm_gmtoff = (val / 100) * 3600 + (val % 100) * 60;
if (neg)
tm->tm_gmtoff = -tm->tm_gmtoff;
}

21
time/tst-strptime2.c
View File

@ -17,8 +17,25 @@ static const struct
{ "1113472456 -1030", -37800 },
{ "1113472456 +0030", 1800 },
{ "1113472456 -0030", -1800 },
{ "1113472456 -1330", LONG_MAX },
{ "1113472456 +1330", LONG_MAX },
{ "1113472456 +1157", 43020 },
{ "1113472456 +1158", 43080 },
{ "1113472456 +1159", 43140 },
{ "1113472456 +1200", 43200 },
{ "1113472456 -1200", -43200 },
{ "1113472456 +1201", 43260 },
{ "1113472456 -1201", -43260 },
{ "1113472456 +1330", 48600 },
{ "1113472456 -1330", -48600 },
{ "1113472456 +1400", 50400 },
{ "1113472456 +1401", 50460 },
{ "1113472456 -2459", -89940 },
{ "1113472456 -2500", -90000 },
{ "1113472456 +2559", 93540 },
{ "1113472456 +2600", 93600 },
{ "1113472456 -99", -356400 },
{ "1113472456 +99", 356400 },
{ "1113472456 -9959", -359940 },
{ "1113472456 +9959", 359940 },
{ "1113472456 -1060", LONG_MAX },
{ "1113472456 +1060", LONG_MAX },
{ "1113472456 1030", LONG_MAX },