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 079954d7f0b13cf116a4a59cedceb99383d855f6..5ba9dd88e72dbc57c470fe9a4887fe0e044f3a25 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 36540ec456399fb729cede40bd4c5cba5ee7a4be..346fc172e72f2e06fb187855a6b65e2b8b8fcf4a 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 32940b4daa5abce9b756344e26fbac49c9f12e88..bf9c40933cc8dd0ae241c9823a5875ba24b1dfdd 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;