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Commit46c79df

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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 parentc027d84 commit46c79df

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2 files changed

+23
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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
@@ -1083,8 +1083,12 @@ int4mod(PG_FUNCTION_ARGS)
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PG_RETURN_NULL();
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}
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1086-
/* SELECT ((-2147483648)::int4) % (-1); causes a floating point exception */
1087-
if (arg1==INT_MIN&&arg2==-1)
1086+
/*
1087+
* 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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*/
1091+
if (arg2==-1)
10881092
PG_RETURN_INT32(0);
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10901094
/* No overflow is possible */
@@ -1107,6 +1111,15 @@ int2mod(PG_FUNCTION_ARGS)
11071111
PG_RETURN_NULL();
11081112
}
11091113

1114+
/*
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* Some machines throw a floating-point exception for INT_MIN % -1, which
1116+
* 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
1118+
* int16, but we might as well have the test for safety.)
1119+
*/
1120+
if (arg2==-1)
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PG_RETURN_INT16(0);
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/* No overflow is possible */
11111124

11121125
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
@@ -657,6 +657,14 @@ int8mod(PG_FUNCTION_ARGS)
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PG_RETURN_NULL();
658658
}
659659

660+
/*
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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.
664+
*/
665+
if (arg2==-1)
666+
PG_RETURN_INT64(0);
667+
660668
/* No overflow is possible */
661669

662670
PG_RETURN_INT64(arg1 %arg2);

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