Unsafe.{get,put}-X-Unaligned; Efficient array comparison intrinsics

Andrew Haley aph at redhat.com
Wed Feb 25 12:49:51 UTC 2015

On 02/25/2015 11:26 AM, Paul Sandoz wrote:

> To your point with the current unsigned byte Lexicographic
> comparator prototype if i were to modify to use the unaligned access
> methods i would want native order and only take the hit of
> reversing, if required, if two elements are not equal.

I agree.

> Note that code will anyway be modified to use a more general array
> mismatch method leveraging the unaligned access methods using native
> order (i cannot think of a reason why it not do otherwise).

It has to: array elements are stored in the same order regardless of
what the hardware does.  So byte-swapping does not help here: it'd
have to be subword-swapping, which some targets support (AArch64 does)
but AFAIK Java doesn't.

I would enormously prefer to solve the simpler problem rather than all
possible versions of related problems.  The model used in bytes.hpp
makes sense IMO.  The issue of non-native endianness is better handled
at a different level from Unsafe in my opinion: that way we can use
native-only intrinsics for the most common machines and reverse bytes
in the caller.  But if the desire is for a full set of native-, big-,
and little-endian methods I can do that.


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