Mike Ash on ARM64

Next time you see someone claiming that Apple’s move to 64-bit with the A7 was a marketing gimmick, point them to this, Mike Ash’s outstanding explanation of the advantages (and trade-offs) ARM64 has brought to iOS 7. Just one bit:

Adding it all together, it’s a pretty big win. My casual benchmarking indicates that basic object creation and destruction takes about 380ns on a 5S running in 32-bit mode, while it’s only about 200ns when running in 64-bit mode. If any instance of the class has ever had a weak reference and an associated object set, the 32-bit time rises to about 480ns, while the 64-bit time remains around 200ns for any instances that were not themselves the target.

In short, the improvements to Apple’s runtime make it so that object allocation in 64-bit mode costs only 40-50% of what it does in 32-bit mode. If your app creates and destroys a lot of objects, that’s a big deal.

★ Saturday, 28 September 2013