Avoid integer overflow hazard in interval_time().

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

2 files changed, 14 insertions, 0 deletions

diff --git a/src/test/regress/expected/horology.out b/src/test/regress/expected/horology.out
index e63e5b30fee..8f52661096f 100644
--- a/src/test/regress/expected/horology.out
+++ b/src/test/regress/expected/horology.out
@@ -981,6 +981,18 @@ SELECT CAST(interval '02:03' AS time) AS "02:03:00";
  02:03:00
 (1 row)
 
+SELECT CAST(interval '-02:03' AS time) AS "21:57:00";
+ 21:57:00 
+----------
+ 21:57:00
+(1 row)
+
+SELECT CAST(interval '-9223372022400000000 us' AS time) AS "00:00:00";
+ 00:00:00 
+----------
+ 00:00:00
+(1 row)
+
 SELECT time '01:30' + interval '02:01' AS "03:31:00";
  03:31:00 
 ----------
diff --git a/src/test/regress/sql/horology.sql b/src/test/regress/sql/horology.sql
index f7f8c8d2dd9..39a35a6b7ce 100644
--- a/src/test/regress/sql/horology.sql
+++ b/src/test/regress/sql/horology.sql
@@ -182,6 +182,8 @@ SELECT d1 - interval '1 year' AS one_year FROM TIMESTAMPTZ_TBL;
 
 SELECT CAST(time '01:02' AS interval) AS "+01:02";
 SELECT CAST(interval '02:03' AS time) AS "02:03:00";
+SELECT CAST(interval '-02:03' AS time) AS "21:57:00";
+SELECT CAST(interval '-9223372022400000000 us' AS time) AS "00:00:00";
 SELECT time '01:30' + interval '02:01' AS "03:31:00";
 SELECT time '01:30' - interval '02:01' AS "23:29:00";
 SELECT time '02:30' + interval '36:01' AS "14:31:00";