64 bit pointers needed
vmikheev at excelsior-usa.com
Fri May 11 06:38:42 UTC 2012
Such a radical change in the language is unlikely feasible.
Maybe, resurrection of JSR-83
implemented via compiler intrinsics would be a viable option.
A motivation why it was rejected ("The proposal requires at least 82 new
classes, and this seems inappropriate for the J2SE core...") looks a
little bit outdated today.
Vitaly V. Mikheev Tel :+7 (383) 330 55 08 (7AM-3PM GMT)
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Excelsior LLC E-mail :vmikheev at excelsior-usa.com
From: discuss-bounces at openjdk.java.net
[mailto:discuss-bounces at openjdk.java.net] On Behalf Of Senseney, Justin
Sent: Friday, May 11, 2012 4:49 AM
To: jep-submit at openjdk.java.net
Cc: OpenJDK discuss; Gandler,William (NIH/CIT) [E]; build-dev build-dev;
compiler-dev at openjdk.java.net
Subject: RFE: 64 bit pointers needed
Title: RFE: 64 bit pointers needed
Author: Justin Senseney
Organization: National Institutes of Health
Owner: Justin Senseney
RFE: 4963452 (4850923, 4880587, 4088441, 6292967)
Discussion: compiler-dev at openjdk.java.net
As per the Java Language Specification, section 10.4, all array access
in Java is done by using an int as index. Since an int is a signed 32bit
value, this limits the total number of addressable elements of an array
to 2**31 (about 2 billion). It should be possible to address an array
using 64bit values.
Improved handling of large datasets that need to be stored in contiguous
Not changing existing range of Integer
Able to compile boolean a = new boolean[Long.MAX_VALUE];
While having access to 2 billion entries may seem sufficient, there are
very compelling performance reasons to be able to use more in a single
array. As an example, consider a square n*n matrix, stored as an array
(either row or column major, doesn't matter which). Since an array
stores at most 2**31 entries, this means that n=sqrt(2**31)=46341, thus
the matrix cannot be very large. For multidimensional arrays this is an
even more severe limitation (3d Tensors could at most be of size 1290).
The scope of this work is extensive, however the solution may be quite
A workaround is to use an array of arrays (ie. double). However
there is no guarantee that successive rows will be laid of linearly in
memory, and therefore performance may be severely penalized.
Experimentally, performance may suffer by a factor of over 2, often far
Also, most existing matrix packages (ie. LAPACK) assumes linear storage,
and are thus incompatible with a double storage (requires double).
Calling a LAPACK routine with a jagged storage thus requires extra array
copying and memory allocation, and can further decrease performance and
increase memory requirements.
It should be possible to address arrays using 64bit integers (long?), as
this provides a seamless transition for users of 64bit computers.
Risks and Assumptions
Use of array of array constructs (use double instead of double)
possible as workaround. This feature is well implemented in C/C++
without any problem, so should be quite technically feasible to
My group has requested this feature for several years. It is currently
listed as one of the top 25 RFEs on http://bugs.sun.com/top25_rfes.do.
Please help Java maintain its relevance by implementing this. I have
several image processing applications that are severely limited by this
bug, these images cannot be opened in most Java applications. These
include electron microscopy and micro-CT images where storage of a
single slice requires more entries than allowable in a Java array.
Thank you for considering this RFE,
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