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| author |  Flavio Toffalini | 2026-10-26 09:03:57 +0000 |
|---|---|---|
| committer |  Nikias Bassen | 2026-11-06 10:29:06 +0100 |
| commit | 1d3b54c784da260f71d885f5f560d69c211a645e (patch) | |
| tree | 6aa7b84ae67249d740bd4c43500a349e403ca2e6 /src/plist.c | |
| parent | 9fdbf585f47501ba19a53fd4bb382d5b533e3fdd (diff) | |
| download | libplist-1d3b54c784da260f71d885f5f560d69c211a645e.tar.gz libplist-1d3b54c784da260f71d885f5f560d69c211a645e.tar.bz2 | |
plist: fix the (sec, usec) date API round trip
plist_set_date_val stores val = sec + usec / 1000000, but
plist_get_date_val splits it with a truncating cast and fabs():
*sec = (int32_t)val;
val = fabs((val - (int64_t)val) * 1000000);
*usec = (int32_t)val;
Two results are wrong. The product is truncated, so set(5, 6) reads
back as (5, 5) - 29.3% of round trips over sec in [0, 3] come back a
microsecond short. And for a negative value, truncation toward zero
plus fabs() give a pair that does not denote the same instant:
set(-3, 250000) stores -2.75 and reads back as (-2, 750000), which the
setter would store as -1.25. Every round trip with sec < 0 and
usec != 0 is wrong.
(int32_t)val is also undefined when the stored value is outside the
int32_t range.
Round the seconds down, round the fraction to microseconds carrying
1000000 into the seconds, and clamp the seconds before converting, so
sec + usec / 1000000 == val to the microsecond with 0 <= usec <
1000000 - the convention the setter uses.
Add test/date_val.c covering fixed cases and a sweep over sec in
[-2, 2]. It fails on an unmodified tree - set(5, 6), set(-3, 250000)
and set(-1, 1) all come back as different instants - and passes with
this change, with make check at 44/44.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Arn4YaWtcQBDsQuJtyBmFP
Diffstat (limited to 'src/plist.c')
| -rw-r--r-- | src/plist.c | 20 |
1 files changed, 15 insertions, 5 deletions
diff --git a/src/plist.c b/src/plist.c index 677e94e..85c2338 100644 --- a/src/plist.c +++ b/src/plist.c @@ -1889,13 +1889,23 @@ void plist_get_date_val(plist_t node, int32_t * sec, int32_t * usec) return; plist_get_type_and_value(node, &type, (void *) &val, &length); assert(length == sizeof(double)); + /* Inverse of plist_set_date_val (val = sec + usec / 1000000): + * whole seconds rounded down, the fraction rounded to microseconds. */ + double whole = floor(val); + double frac_usec = round((val - whole) * 1000000); + if (frac_usec >= 1000000) { + whole += 1; + frac_usec -= 1000000; + } + /* keep the int32_t conversion defined */ + if (whole > INT32_MAX) + whole = INT32_MAX; + else if (whole < INT32_MIN) + whole = INT32_MIN; if (sec) - *sec = (int32_t)val; + *sec = (int32_t)whole; if (usec) - { - val = fabs((val - (int64_t)val) * 1000000); - *usec = (int32_t)val; - } + *usec = (int32_t)frac_usec; } void plist_get_unix_date_val(plist_t node, int64_t *sec) |