Add unchecked-divide, unchecked-remainder

Description

This appears like it might be an oversight that these are missing. There are unchecked-divide-int and unchecked-remainder-int functions, but not equivalents for longs, even though there are equivalents for longs for every other unchecked operation. The JVM has bytecodes for long division and remainder.

The Clojure documentation in the section "Support for Java Primitives" on page http://clojure.org/java_interop has links for unchecked-divide and unchecked-remainder, but since they don't exist in Clojure, the API link targets don't exist.

It seems like a good idea to either add these to Clojure, or remove them from the documentation.

Environment

None

Activity

Show:
Colin Taylor
October 5, 2014, 4:19 AM

user=> (dotimes [_ 6] (time (dotimes [_ 50000000] (unchecked-divide 4 (System/currentTimeMillis)))))
"Elapsed time: 1806.942 msecs"
"Elapsed time: 1808.747 msecs"
"Elapsed time: 1865.074 msecs"
"Elapsed time: 1802.777 msecs"
"Elapsed time: 1839.468 msecs"
"Elapsed time: 1830.61 msecs"
nil
user=> (dotimes [_ 6] (time (dotimes [_ 50000000] (/ 4 (System/currentTimeMillis)))))
"Elapsed time: 5003.598 msecs"
"Elapsed time: 4998.182 msecs"
"Elapsed time: 4941.237 msecs"
"Elapsed time: 5036.517 msecs"
"Elapsed time: 4965.867 msecs"
"Elapsed time: 4982.693 msecs"

Alex Miller
October 5, 2014, 4:19 AM

The current results are the same with either unchecked-math setting, but I see your point.

Refreshing my memory of the (/ Long/MIN_VALUE -1) case, I think you're right. The (new) unchecked-divide / remainder should do what the current (checked) forms do and the regular division and remainder cases should be making the overflow check. I think CLJ-1254 should cover the quot changes.

Andy Fingerhut
October 5, 2014, 1:42 AM

Alex, did you do the testing in your previous comment with *unchecked-math* true or false? If false, then I would think that if CLJ-1254 is judged a bug, then the behavior you saw is a bug, too, that misses the same corner case.

Alex Miller
October 5, 2014, 1:24 AM

The patch format looks better. Pulling out farther to the ticket itself, afaict Clojure will already use the right byteocode for checked or unchecked so this may not even be needed?

If I compile (without the patch):

then the bytecode for that fn is:

similarly, quot of two longs yields the same code but with lrem. I think patch has no net effect on the resulting bytecode?

Colin Taylor
October 4, 2014, 10:47 PM

Uggh, sorry Alex.

New patch with better commit message.

Your pinned fields
Click on the next to a field label to start pinning.

Assignee

Colin Taylor

Reporter

Andy Fingerhut

Labels

Approval

Triaged

Patch

Code and Test

Priority

Major

Affects versions