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//! Run-time feature detection for ARM on Linux.
use super::{auxvec, cpuinfo};
use crate::detect::{bit, cache, Feature};
/// Performs run-time feature detection.
#[inline]
pub fn check_for(x: Feature) -> bool {
cache::test(x as u32, detect_features)
}
/// Try to read the features from the auxiliary vector, and if that fails, try
/// to read them from /proc/cpuinfo.
fn detect_features() -> cache::Initializer {
let mut value = cache::Initializer::default();
let enable_feature = |value: &mut cache::Initializer, f, enable| {
if enable {
value.set(f as u32);
}
};
// The values are part of the platform-specific [asm/hwcap.h][hwcap]
//
// [hwcap]: https://github.com/torvalds/linux/blob/master/arch/arm64/include/uapi/asm/hwcap.h
if let Ok(auxv) = auxvec::auxv() {
enable_feature(&mut value, Feature::neon, bit::test(auxv.hwcap, 12));
enable_feature(&mut value, Feature::pmull, bit::test(auxv.hwcap2, 1));
return value;
}
if let Ok(c) = cpuinfo::CpuInfo::new() {
enable_feature(
&mut value,
Feature::neon,
c.field("Features").has("neon") && !has_broken_neon(&c),
);
enable_feature(&mut value, Feature::pmull, c.field("Features").has("pmull"));
return value;
}
value
}
/// Is the CPU known to have a broken NEON unit?
///
/// See https://crbug.com/341598.
fn has_broken_neon(cpuinfo: &cpuinfo::CpuInfo) -> bool {
cpuinfo.field("CPU implementer") == "0x51"
&& cpuinfo.field("CPU architecture") == "7"
&& cpuinfo.field("CPU variant") == "0x1"
&& cpuinfo.field("CPU part") == "0x04d"
&& cpuinfo.field("CPU revision") == "0"
}
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