问题
So it's fairly easy to figure out what kind of CPU an iOS device runs by querying sysctlbyname("hw.cpusubtype", ...), but there seems to be no obvious way to figure out what features the CPU actually has (think VFP, NEON, Thumb, ...). Can someone think of a way to do this?
Basically, what I need is something similar to getauxval(AT_HWCAP) on Linux/Android, which returns a bit mask of features supported by the CPU.
A few things to note:
- The information must be retrieved at runtime from the OS. No preprocessor defines.
- Fat binaries is not a solution. I really do need to know this stuff in an ARM v6 binary.
Thanks in advance!
回答1:
sysctlbyname has “hw.optional.neon”. I do not see a name for VFP, except “hw.optional.vfp_shortvector”, which is a deprecated feature.
回答2:
Do a matrix float multiplaction via accelerate.framework and measure the execution time. The difference will be huge enough between Neon and VFP driven math, you simply cannot miss.
Thumb is always there, and the presence of NEON means armv7= Thumb2.
回答3:
First, consider carefully whether or not you really need to support armv6 binaries for iOS. According to published version share statistics, something like 98.5% of iOS devices are running iOS 5.0 or later, which does not support armv6 devices (armv6 binaries will still run on current iOS versions, obviously, but all new apps should really be targeting armv7; there’s basically zero reason for your customers to be shipping armv6 binaries for iOS today).
Similarly, your concerns about code size are misplaced. If you provide a fat library, and your customer builds an armv6 binary against it, only the armv6 bits of your library will be built into their application. Furthermore, code size is usually a nearly trivial fraction of application bundle size; most of the size of an application comes from other resources.
Ok. All that aside, if you really want to pursue this: VFP and thumb are supported on all iOS devices, so there’s no need to check for support. You can check for NEON and thumb-2 using the method that Eric Postpischil suggested (all armv7 iOS devices have NEON support, so availability of NEON coincides exactly with availability of thumb-2).
来源：https://stackoverflow.com/questions/17712590/is-there-a-way-to-detect-vfp-neon-thumb-on-ios-at-runtime