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Commit2e06d52

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Fix the int8 and int2 cases of (minimum possible integer) % (-1).
The correct answer for this (or any other case with arg2 = -1) is zero,but some machines throw a floating-point exception instead of behavingsanely. Commitf9ac414 dealt with thisin int4mod, but overlooked the fact that it also happens in int8mod(at least on my Linux x86_64 machine). Protect int2mod as well; it'snot clear whether any machines fail there (mine does not) but since thetest is so cheap it seems better safe than sorry. While at it, simplifythe original guard in int4mod: we need only check for arg2 == -1, wedon't need to check arg1 explicitly.Xi Wang, with some editing by me.
1 parent797ea52 commit2e06d52

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2 files changed

+23
-2
lines changed

2 files changed

+23
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lines changed

‎src/backend/utils/adt/int.c‎

Lines changed: 15 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1094,8 +1094,12 @@ int4mod(PG_FUNCTION_ARGS)
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PG_RETURN_NULL();
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}
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1097-
/* SELECT ((-2147483648)::int4) % (-1); causes a floating point exception */
1098-
if (arg1==INT_MIN&&arg2==-1)
1097+
/*
1098+
* Some machines throw a floating-point exception for INT_MIN % -1, which
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* is a bit silly since the correct answer is perfectly well-defined,
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* namely zero.
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*/
1102+
if (arg2==-1)
10991103
PG_RETURN_INT32(0);
11001104

11011105
/* No overflow is possible */
@@ -1118,6 +1122,15 @@ int2mod(PG_FUNCTION_ARGS)
11181122
PG_RETURN_NULL();
11191123
}
11201124

1125+
/*
1126+
* Some machines throw a floating-point exception for INT_MIN % -1, which
1127+
* is a bit silly since the correct answer is perfectly well-defined,
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* namely zero. (It's not clear this ever happens when dealing with
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* int16, but we might as well have the test for safety.)
1130+
*/
1131+
if (arg2==-1)
1132+
PG_RETURN_INT16(0);
1133+
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/* No overflow is possible */
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11231136
PG_RETURN_INT16(arg1 %arg2);

‎src/backend/utils/adt/int8.c‎

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -651,6 +651,14 @@ int8mod(PG_FUNCTION_ARGS)
651651
PG_RETURN_NULL();
652652
}
653653

654+
/*
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* Some machines throw a floating-point exception for INT64_MIN % -1,
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* which is a bit silly since the correct answer is perfectly
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* well-defined, namely zero.
658+
*/
659+
if (arg2==-1)
660+
PG_RETURN_INT64(0);
661+
654662
/* No overflow is possible */
655663

656664
PG_RETURN_INT64(arg1 %arg2);

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