Fix corner-case 64-bit integer subtraction bug on some platforms.

When computing "0 - INT64_MIN", most platforms would report an
overflow error, which is correct. However, platforms without integer
overflow builtins or 128-bit integers would fail to spot the overflow,
and incorrectly return INT64_MIN.

Back-patch to all supported branches.

Patch be me. Thanks to Jian He for initial investigation, and Laurenz
Albe and Tom Lane for review.

Discussion: https://postgr.es/m/CAEZATCUNK-AZSD0jVdgkk0N%3DNcAXBWeAEX-QU9AnJPensikmdQ%40mail.gmail.com

diff --git a/src/include/common/int.h b/src/include/common/int.h
index a2972218e7216c920d16661ad695877e4e82c004..4c862651f5dad517c70fe904c227e06d9ae74abe 100644 (file)
--- a/src/include/common/int.h
+++ b/src/include/common/int.h
@@ -200,8 +200,12 @@ pg_sub_s64_overflow(int64 a, int64 b, int64 *result)
        *result = (int64) res;
        return false;
 #else
+       /*
+        * Note: overflow is also possible when a == 0 and b < 0 (specifically,
+        * when b == PG_INT64_MIN).
+        */
        if ((a < 0 && b > 0 && a < PG_INT64_MIN + b) ||
-               (a > 0 && b < 0 && a > PG_INT64_MAX + b))
+               (a >= 0 && b < 0 && a > PG_INT64_MAX + b))
        {
                *result = 0x5EED;               /* to avoid spurious warnings */
                return true;

diff --git a/src/test/regress/expected/int8.out b/src/test/regress/expected/int8.out
index 813e3a828663526ec739d2e9a5111640052da89f..1bc3776208e734d50631661b25d2679bf9d357b6 100644 (file)
--- a/src/test/regress/expected/int8.out
+++ b/src/test/regress/expected/int8.out
@@ -659,6 +659,8 @@ select -('-9223372036854775807'::int8);
 
 select -('-9223372036854775808'::int8);
 ERROR:  bigint out of range
+select 0::int8 - '-9223372036854775808'::int8;
+ERROR:  bigint out of range
 select '9223372036854775800'::int8 + '9223372036854775800'::int8;
 ERROR:  bigint out of range
 select '-9223372036854775800'::int8 + '-9223372036854775800'::int8;

diff --git a/src/test/regress/sql/int8.sql b/src/test/regress/sql/int8.sql
index dba3ade687ac422e0683d3a3ab9ef05cf6bcbfba..29712209d58b88bad4536c6f983254641344320d 100644 (file)
--- a/src/test/regress/sql/int8.sql
+++ b/src/test/regress/sql/int8.sql
@@ -131,6 +131,7 @@ select '9223372036854775808'::int8;
 
 select -('-9223372036854775807'::int8);
 select -('-9223372036854775808'::int8);
+select 0::int8 - '-9223372036854775808'::int8;
 
 select '9223372036854775800'::int8 + '9223372036854775800'::int8;
 select '-9223372036854775800'::int8 + '-9223372036854775800'::int8;