CPU features
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There are several ways to check for CPU features in your code, each with a
different set of trade-offs.
ABI: Use the preprocessor's pre-defined macros
It's usually most convenient to determine the ABI at build time using #ifdef
in conjunction with:
__arm__ for 32-bit ARM__aarch64__ for 64-bit ARM__i386__ for 32-bit X86__x86_64__ for 64-bit X86
Note that 32-bit X86 is called __i386__, not __x86__ as you might expect!
CPU core counts: Use libc's sysconf(3)
sysconf(3) lets you
query both _SC_NPROCESSORS_CONF (the number of CPU cores in the system)
and _SC_NPROCESSORS_ONLN (the number of CPU cores currently online).
Features: Use libc's getauxval(3)
In API level 18 and newer,
getauxval(3)
is available in Android's C library. The AT_HWCAP and AT_HWCAP2 arguments
return bitmasks listing CPU-specific features. See the various hwcap.h
headers in the NDK for the constants to compare against, such as HWCAP_SHA512
for arm64's SHA512 instructions, or HWCAP_IDIVT for arm's Thumb integer
division instructions.
The Google cpu_features library
One problem with AT_HWCAP is that sometimes devices are mistaken. Some old
devices, for example, claim to have integer division instructions but do not.
Google's cpu_features library works
around such issues by applying its own knowledge of specific SoCs (by parsing
/proc/cpuinfo to work out the specific SoC in question).
This library is maintained for use by Google's first-party app teams, and
has workarounds for every problematic device they've encountered in the wild.
The NDK cpufeatures library (deprecated)
The NDK still provides a deprecated library named cpufeatures for source
compatibility with apps that already use it. Unlike the newer and more complete
cpu_features library, this historical
library does not have workarounds for as many specific SoCs.
Content and code samples on this page are subject to the licenses described in the Content License. Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
Last updated 2021-11-16 UTC.
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