ARM64 Assembly with Swift and XCode

This code shows a simple bit of embedded ARM64 assembly code in an iOS application. It provides a working demo for my blog post at MikeJfromVA.com.

What's Here?

• ViewController.swift wires the text entry and text label fields together with the button and does some basic input validation.
• popcount.c uses a basic shift-and-compare technique to compute the population count. It is only compiled when the XCode Target is Simulator.
• popcount.s uses cnt, an Aarch64 instruction, to compute the population count. It is only compiled when the XCode Target is a physical device.
• ArmAssembly-Bridging-Header.h provides the function header for both popcount.c and popcount.s.
• SimpleFunction.swift does not actually play a role in the app directly. Compile this into assembly (xcrun -sdk iphoneos swiftc -emit-assembly -target arm64-apple-ios11.0 SimpleFunction.swift) to see some ARM64 operations. Used this as a template for popcount.s.
• ARMAssemblyTests.swift contains a simple unit test. Run on device and in simulator to test both popcount.c and popcount.s.