Details
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Type:
Defect
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Status:
Closed
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Priority:
Minor
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Resolution: Completed
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Affects Version/s: Release 1.5
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Fix Version/s: Release 1.8
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Component/s: None
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Patch:Code and Test
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Approval:Ok
Description
In Clojure 1.5.1, see the following undesirable behavior regarding incorrect quot results for BigInts:
user=> (quot Long/MIN_VALUE -1N) -9223372036854775808N user=> (quot (bigint Long/MIN_VALUE) -1) -9223372036854775808N
Similar issue to CLJ-1222. The root cause is that Java division of longs gives a numerically incorrect answer of Long.MIN_VALUE for (Long.MIN_VALUE / -1), because the numerically correct answer does not fit in a long. I believe this is the only pair of arguments for long division that gives a numerically incorrect answer, because division with a denominator having an absolute value of 2 or more gives a result closer to 0 than the numerator, and everything works fine for a denominator of 1 or -1, except this one case.
Related issues: CLJ-1222 for multiply, CLJ-1253 for / on longs, CLJ-1254 for quot on longs
Patch: clj-1225-2.txt
Screened by: Alex Miller
Patch clj-1225-fix-division-overflow-patch-v1.txt dated Jun 25 2013 may be one good way to address this issue. It modifies quot and / to return the numerically correct (BigInt) answer when given args Long/MIN_VALUE and -1.
It also removes the quotient intrinsic that does a JVM LDIV operation on longs for quot, since that operation is one of those that gives the incorrect result. I have not done any performance testing with this patch yet, but I have verified that it does not introduce any new reflection warnings when compiling Clojure itself.