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mktime: avoid signed integer overflow

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* time/mktime.c (__mktime_internal): Do not mishandle the case
where diff == INT_MIN.
This commit is contained in:
Paul Eggert 2012-03-16 03:18:12 -07:00
parent 94c7d826c9
commit f8591f8049
2 changed files with 8 additions and 4 deletions
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4
ChangeLog
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@ -1,5 +1,9 @@
2012-05-23 Paul Eggert <eggert@cs.ucla.edu> 2012-05-23 Paul Eggert <eggert@cs.ucla.edu>
mktime: avoid signed integer overflow
* time/mktime.c (__mktime_internal): Do not mishandle the case
where diff == INT_MIN.
mktime: simplify computation of average mktime: simplify computation of average
* time/mktime.c (ranged_convert): Use new time_t_avg function * time/mktime.c (ranged_convert): Use new time_t_avg function
instead of rolling our own (probably-slower) code. instead of rolling our own (probably-slower) code.

8
time/mktime.c
View File

@ -445,7 +445,7 @@ __mktime_internal (struct tm *tp,
int approx_biennia = SHR (t0, ALOG2_SECONDS_PER_BIENNIUM); int approx_biennia = SHR (t0, ALOG2_SECONDS_PER_BIENNIUM);
int diff = approx_biennia - approx_requested_biennia; int diff = approx_biennia - approx_requested_biennia;
int abs_diff = diff < 0 ? - diff : diff; int approx_abs_diff = diff < 0 ? -1 - diff : diff;
/* IRIX 4.0.5 cc miscalculates TIME_T_MIN / 3: it erroneously /* IRIX 4.0.5 cc miscalculates TIME_T_MIN / 3: it erroneously
gives a positive value of 715827882. Setting a variable gives a positive value of 715827882. Setting a variable
@ -456,15 +456,15 @@ __mktime_internal (struct tm *tp,
time_t overflow_threshold = time_t overflow_threshold =
(time_t_max / 3 - time_t_min / 3) >> ALOG2_SECONDS_PER_BIENNIUM; (time_t_max / 3 - time_t_min / 3) >> ALOG2_SECONDS_PER_BIENNIUM;
if (overflow_threshold < abs_diff) if (overflow_threshold < approx_abs_diff)
{ {
/* Overflow occurred. Try repairing it; this might work if /* Overflow occurred. Try repairing it; this might work if
the time zone offset is enough to undo the overflow. */ the time zone offset is enough to undo the overflow. */
time_t repaired_t0 = -1 - t0; time_t repaired_t0 = -1 - t0;
approx_biennia = SHR (repaired_t0, ALOG2_SECONDS_PER_BIENNIUM); approx_biennia = SHR (repaired_t0, ALOG2_SECONDS_PER_BIENNIUM);
diff = approx_biennia - approx_requested_biennia; diff = approx_biennia - approx_requested_biennia;
abs_diff = diff < 0 ? - diff : diff; approx_abs_diff = diff < 0 ? -1 - diff : diff;
if (overflow_threshold < abs_diff) if (overflow_threshold < approx_abs_diff)
return -1; return -1;
guessed_offset += repaired_t0 - t0; guessed_offset += repaired_t0 - t0;
t0 = repaired_t0; t0 = repaired_t0;