

Samsung will go 64 bit - what about Android? - auggierose
http://www.theguardian.com/technology/2013/sep/12/samsung-apple-64-bit-smartphone

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pohl
_...experts puzzle over benefit of 64-bit functions_

Let's try to enumerate whatever we can think of:

The most commonly mentioned one is addressing 4GB of memory and larger, which
doesn't apply to the 5S. (It's my understanding that it only contains 2GB). So
that one is rightfully dismissed. Well, other than that you get more benefit
from ASLR (Address Space Layout Randomization) with a 64bit virtual address
space. Still not a headline-feature, though.

It's also commonly mentioned that AArch64 defines twice as many general
purpose registers, each twice as large. AArch64 also defines twice as many FP
registers – again, each twice as large – available to the SIMD unit. The
camera in the 5S does a lot of image processing in order to try to take the
best one-button picture possible, and there is probably a lot of opportunity
for SIMD code behind that. So that might be a big win that is directly tied to
user experience.

Also mentioned, but less frequently, is the kind of optimizations a
programming language runtime implementor can do when 64bits are available. For
example: _Apple has apparently taken advantage of the 64-bit runtime in Lion
by optimizing the Objective C runtime itself to use some of these extra bits
for, shall we say, clever purposes. Bavarious describes an optimization
through which Apple is able to replace previously full-fledged opaque objects
such as NSNumber with an object-placeholder that exists entirely as the 64-bit
“object address” itself. This means that, for a wide range of “simple”
objects, no additional memory allocation is required, and no retain /release
memory management is required for the “object.”_

[http://www.red-sweater.com/blog/1947/bit-hacking](http://www.red-
sweater.com/blog/1947/bit-hacking)

(I assume a future version of Dalvik could take advantage of similar tricks.)

AArch64 also adds cryptography instructions for AES and SHA-1/SHA-256. This is
probably the least impressive performance benefit I've seen mentioned.

Am I missing anything?

