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    //! Run-time feature detection

    mod cache;
    mod bit;

    cfg_if! {
        if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
            #[path = "x86.rs"]
            mod arch;
        } else if #[cfg(target_arch = "arm")] {
            #[path = "arm.rs"]
            mod arch;
        } else if #[cfg(target_arch = "aarch64")] {
            #[path = "aarch64.rs"]
            mod arch;
        } else if #[cfg(target_arch = "powerpc64")] {
            #[path = "powerpc64.rs"]
            mod arch;
        } else {
            mod arch {
                pub enum Feature {
                    Null
                }
                pub fn detect_features() -> super::cache::Initializer {
                    Default::default()
                }
            }
        }
    }

    mod linux;

    pub use self::arch::Feature;

    /// Performs run-time feature detection.
    pub fn check_for(x: Feature) -> bool {
        cache::test(x as u32, arch::detect_features)
    }

    #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
    #[macro_export]
    #[unstable(feature = "stdsimd", issue = "0")]
    macro_rules! is_x86_feature_detected {
        ($t:tt) => {
            compile_error!(r#"
    is_x86_feature_detected can only be used on x86 and x86_64 targets.
    You can prevent it from being used in other architectures by
    guarding it behind a cfg(target_arch) as follows:

        #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
            if is_x86_feature_detected(...) { ... }
        }
    "#)
        };
    }

    #[cfg(not(target_arch = "arm"))]
    #[macro_export]
    #[unstable(feature = "stdsimd", issue = "0")]
    macro_rules! is_arm_feature_detected {
        ($t:tt) => {
            compile_error!(r#"
    is_arm_feature_detected can only be used on ARM targets.
    You can prevent it from being used in other architectures by
    guarding it behind a cfg(target_arch) as follows:

        #[cfg(target_arch = "arm")] {
            if is_arm_feature_detected(...) { ... }
        }
    "#)
        };
    }

    #[cfg(not(target_arch = "aarch64"))]
    #[macro_export]
    #[unstable(feature = "stdsimd", issue = "0")]
    macro_rules! is_aarch64_feature_detected {
        ($t:tt) => {
            compile_error!(r#"
    is_aarch64_feature_detected can only be used on AArch64 targets.
    You can prevent it from being used in other architectures by
    guarding it behind a cfg(target_arch) as follows:

        #[cfg(target_arch = "aarch64")] {
            if is_aarch64_feature_detected(...) { ... }
        }
    "#)
        };
    }

    #[cfg(not(target_arch = "powerpc64"))]
    #[macro_export]
    #[unstable(feature = "stdsimd", issue = "0")]
    macro_rules! is_powerpc64_feature_detected {
        ($t:tt) => {
            compile_error!(r#"
    is_powerpc64_feature_detected can only be used on PowerPC64 targets.
    You can prevent it from being used in other architectures by
    guarding it behind a cfg(target_arch) as follows:

        #[cfg(target_arch = "powerpc64")] {
            if is_powerpc64_feature_detected(...) { ... }
        }
    "#)
        };
    }

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