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Avoid integer overflow hazard in interval_time().

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When casting an interval to a time, the original code suffered from
64-bit integer overflow for inputs with a sufficiently large negative
"time" field, leading to bogus results.

Fix by rewriting the algorithm in a simpler form, that more obviously
cannot overflow. While at it, improve the test coverage to include
negative interval inputs.

Discussion: https://postgr.es/m/CAEZATCXoUKHkcuq4q63hkiPsKZJd0kZWzgKtU%2BNT0aU4wbf_Pw%40mail.gmail.com
This commit is contained in:
Dean Rasheed
2023-11-09 12:10:14 +00:00
parent a4f7d33a90
commit 3850d4dec1
3 changed files with 17 additions and 12 deletions
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15
src/backend/utils/adt/date.c
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@@ -2012,19 +2012,10 @@ interval_time(PG_FUNCTION_ARGS)
{
Interval *span = PG_GETARG_INTERVAL_P(0);
TimeADT result;
int64 days;
result = span->time;
if (result >= USECS_PER_DAY)
{
days = result / USECS_PER_DAY;
result -= days * USECS_PER_DAY;
}
else if (result < 0)
{
days = (-result + USECS_PER_DAY - 1) / USECS_PER_DAY;
result += days * USECS_PER_DAY;
}
result = span->time % USECS_PER_DAY;
if (result < 0)
result += USECS_PER_DAY;
PG_RETURN_TIMEADT(result);
}