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

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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
This commit is contained in:
Dean Rasheed 2023-11-09 09:55:39 +00:00
parent 99fa98766f
commit dea12b40d5
3 changed files with 8 additions and 1 deletions
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6
src/include/common/int.h
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@ -200,8 +200,12 @@ pg_sub_s64_overflow(int64 a, int64 b, int64 *result)
*result = (int64) res; *result = (int64) res;
return false; return false;
#else #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) || 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 */ *result = 0x5EED; /* to avoid spurious warnings */
return true; return true;

2
src/test/regress/expected/int8.out
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@ -659,6 +659,8 @@ select -('-9223372036854775807'::int8);
select -('-9223372036854775808'::int8); select -('-9223372036854775808'::int8);
ERROR: bigint out of range ERROR: bigint out of range
select 0::int8 - '-9223372036854775808'::int8;
ERROR: bigint out of range
select '9223372036854775800'::int8 + '9223372036854775800'::int8; select '9223372036854775800'::int8 + '9223372036854775800'::int8;
ERROR: bigint out of range ERROR: bigint out of range
select '-9223372036854775800'::int8 + '-9223372036854775800'::int8; select '-9223372036854775800'::int8 + '-9223372036854775800'::int8;

1
src/test/regress/sql/int8.sql
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@ -131,6 +131,7 @@ select '9223372036854775808'::int8;
select -('-9223372036854775807'::int8); select -('-9223372036854775807'::int8);
select -('-9223372036854775808'::int8); select -('-9223372036854775808'::int8);
select 0::int8 - '-9223372036854775808'::int8;
select '9223372036854775800'::int8 + '9223372036854775800'::int8; select '9223372036854775800'::int8 + '9223372036854775800'::int8;
select '-9223372036854775800'::int8 + '-9223372036854775800'::int8; select '-9223372036854775800'::int8 + '-9223372036854775800'::int8;