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    //! This module implements minimal run-time feature detection for x86.
    //!
    //! The features are detected using the `detect_features` function below.
    //! This function uses the CPUID instruction to read the feature flags from the
    //! CPU and encodes them in an `usize` where each bit position represents
    //! whether a feature is available (bit is set) or unavaiable (bit is cleared).
    //!
    //! The enum `Feature` is used to map bit positions to feature names, and the
    //! the `__crate::arch::detect::check_for!` macro is used to map string literals (e.g.
    //! "avx") to these bit positions (e.g. `Feature::avx`).
    //!
    //!
    //! The run-time feature detection is performed by the
    //! `__crate::arch::detect::check_for(Feature) -> bool` function. On its first call,
    //! this functions queries the CPU for the available features and stores them
    //! in a global `AtomicUsize` variable. The query is performed by just checking
    //! whether the feature bit in this global variable is set or cleared.

    /// A macro to test at *runtime* whether a CPU feature is available on
    /// x86/x86-64 platforms.
    ///
    /// This macro is provided in the standard library and will detect at runtime
    /// whether the specified CPU feature is detected. This does *not* resolve at
    /// compile time unless the specified feature is already enabled for the entire
    /// crate. Runtime detection currently relies mostly on the `cpuid` instruction.
    ///
    /// This macro only takes one argument which is a string literal of the feature
    /// being tested for. The feature names supported are the lowercase versions of
    /// the ones defined by Intel in [their documentation][docs].
    ///
    /// ## Supported arguments
    ///
    /// This macro supports the same names that `#[target_feature]` supports. Unlike
    /// `#[target_feature]`, however, this macro does not support names separated
    /// with a comma. Instead testing for multiple features must be done through
    /// separate macro invocations for now.
    ///
    /// Supported arguments are:
    ///
    /// * `"aes"`
    /// * `"pclmulqdq"`
    /// * `"rdrand"`
    /// * `"rdseed"`
    /// * `"tsc"`
    /// * `"mmx"`
    /// * `"sse"`
    /// * `"sse2"`
    /// * `"sse3"`
    /// * `"ssse3"`
    /// * `"sse4.1"`
    /// * `"sse4.2"`
    /// * `"sse4a"`
    /// * `"sha"`
    /// * `"avx"`
    /// * `"avx2"`
    /// * `"avx512f"`
    /// * `"avx512cd"`
    /// * `"avx512er"`
    /// * `"avx512pf"`
    /// * `"avx512bw"`
    /// * `"avx512dq"`
    /// * `"avx512vl"`
    /// * `"avx512ifma"`
    /// * `"avx512vbmi"`
    /// * `"avx512vpopcntdq"`
    /// * `"fma"`
    /// * `"bmi1"`
    /// * `"bmi2"`
    /// * `"abm"`
    /// * `"lzcnt"`
    /// * `"tbm"`
    /// * `"popcnt"`
    /// * `"fxsr"`
    /// * `"xsave"`
    /// * `"xsaveopt"`
    /// * `"xsaves"`
    /// * `"xsavec"`
    ///
    /// [docs]: https://software.intel.com/sites/landingpage/IntrinsicsGuide
    #[macro_export]
    #[stable(feature = "simd_x86", since = "1.27.0")]
    #[allow_internal_unstable]
    macro_rules! is_x86_feature_detected {
        ("aes") => {
            cfg!(target_feature = "aes") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::aes)  };
        ("pclmulqdq") => {
            cfg!(target_feature = "pclmulqdq") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::pclmulqdq)  };
        ("rdrand") => {
            cfg!(target_feature = "rdrand") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::rdrand)  };
        ("rdseed") => {
            cfg!(target_feature = "rdseed") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::rdseed)  };
        ("tsc") => {
            cfg!(target_feature = "tsc") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::tsc)  };
        ("mmx") => {
            cfg!(target_feature = "mmx") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::mmx)  };
        ("sse") => {
            cfg!(target_feature = "sse") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::sse)  };
        ("sse2") => {
            cfg!(target_feature = "sse2") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::sse2)
        };
        ("sse3") => {
            cfg!(target_feature = "sse3") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::sse3)
        };
        ("ssse3") => {
            cfg!(target_feature = "ssse3") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::ssse3)
        };
        ("sse4.1") => {
            cfg!(target_feature = "sse4.1") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::sse4_1)
        };
        ("sse4.2") => {
            cfg!(target_feature = "sse4.2") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::sse4_2)
        };
        ("sse4a") => {
            cfg!(target_feature = "sse4a") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::sse4a)
        };
        ("sha") => {
            cfg!(target_feature = "sha") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::sha)
        };
        ("avx") => {
            cfg!(target_feature = "avx") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx)
        };
        ("avx2") => {
            cfg!(target_feature = "avx2") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx2)
        };
        ("avx512f") => {
            cfg!(target_feature = "avx512f") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx512f)
        };
        ("avx512cd") => {
            cfg!(target_feature = "avx512cd") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx512cd)
        };
        ("avx512er") => {
            cfg!(target_feature = "avx512er") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx512er)
        };
        ("avx512pf") => {
            cfg!(target_feature = "avx512pf") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx512pf)
        };
        ("avx512bw") => {
            cfg!(target_feature = "avx512bw") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx512bw)
        };
        ("avx512dq") => {
            cfg!(target_feature = "avx512dq") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx512dq)
        };
        ("avx512vl") => {
            cfg!(target_Feature = "avx512vl") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx512vl)
        };
        ("avx512ifma") => {
            cfg!(target_feature = "avx512ifma") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx512_ifma)
        };
        ("avx512vbmi") => {
            cfg!(target_feature = "avx512vbmi") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx512_vbmi)
        };
        ("avx512vpopcntdq") => {
            cfg!(target_feature = "avx512vpopcntdq") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::avx512_vpopcntdq)
        };
        ("fma") => {
            cfg!(target_feature = "fma") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::fma)
        };
        ("bmi1") => {
            cfg!(target_feature = "bmi1") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::bmi)
        };
        ("bmi2") => {
            cfg!(target_feature = "bmi2") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::bmi2)
        };
        ("abm") => {
            cfg!(target_feature = "abm") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::abm)
        };
        ("lzcnt") => {
            cfg!(target_feature = "lzcnt") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::abm)
        };
        ("tbm") => {
            cfg!(target_feature = "tbm") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::tbm)
        };
        ("popcnt") => {
            cfg!(target_feature = "popcnt") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::popcnt)
        };
        ("fxsr") => {
            cfg!(target_feature = "fxsr") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::fxsr)
        };
        ("xsave") => {
            cfg!(target_feature = "xsave") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::xsave)
        };
        ("xsaveopt") => {
            cfg!(target_feature = "xsaveopt") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::xsaveopt)
        };
        ("xsaves") => {
            cfg!(target_feature = "xsaves") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::xsaves)
        };
        ("xsavec") => {
            cfg!(target_feature = "xsavec") || $crate::arch::detect::check_for(
                $crate::arch::detect::Feature::xsavec)
        };
        ($t:tt) => {
            compile_error!(concat!("unknown target feature: ", $t))
        };
    }

    /// X86 CPU Feature enum. Each variant denotes a position in a bitset for a
    /// particular feature.
    ///
    /// This is an unstable implementation detail subject to change.
    #[allow(non_camel_case_types)]
    #[repr(u8)]
    #[doc(hidden)]
    #[unstable(feature = "stdsimd_internal", issue = "0")]
    pub enum Feature {
        /// AES (Advanced Encryption Standard New Instructions AES-NI)
        aes,
        /// CLMUL (Carry-less Multiplication)
        pclmulqdq,
        /// RDRAND
        rdrand,
        /// RDSEED
        rdseed,
        /// TSC (Time Stamp Counter)
        tsc,
        /// MMX
        mmx,
        /// SSE (Streaming SIMD Extensions)
        sse,
        /// SSE2 (Streaming SIMD Extensions 2)
        sse2,
        /// SSE3 (Streaming SIMD Extensions 3)
        sse3,
        /// SSSE3 (Supplemental Streaming SIMD Extensions 3)
        ssse3,
        /// SSE4.1 (Streaming SIMD Extensions 4.1)
        sse4_1,
        /// SSE4.2 (Streaming SIMD Extensions 4.2)
        sse4_2,
        /// SSE4a (Streaming SIMD Extensions 4a)
        sse4a,
        /// SHA
        sha,
        /// AVX (Advanced Vector Extensions)
        avx,
        /// AVX2 (Advanced Vector Extensions 2)
        avx2,
        /// AVX-512 F (Foundation)
        avx512f,
        /// AVX-512 CD (Conflict Detection Instructions)
        avx512cd,
        /// AVX-512 ER (Exponential and Reciprocal Instructions)
        avx512er,
        /// AVX-512 PF (Prefetch Instructions)
        avx512pf,
        /// AVX-512 BW (Byte and Word Instructions)
        avx512bw,
        /// AVX-512 DQ (Doubleword and Quadword)
        avx512dq,
        /// AVX-512 VL (Vector Length Extensions)
        avx512vl,
        /// AVX-512 IFMA (Integer Fused Multiply Add)
        avx512_ifma,
        /// AVX-512 VBMI (Vector Byte Manipulation Instructions)
        avx512_vbmi,
        /// AVX-512 VPOPCNTDQ (Vector Population Count Doubleword and
        /// Quadword)
        avx512_vpopcntdq,
        /// FMA (Fused Multiply Add)
        fma,
        /// BMI1 (Bit Manipulation Instructions 1)
        bmi,
        /// BMI1 (Bit Manipulation Instructions 2)
        bmi2,
        /// ABM (Advanced Bit Manipulation) on AMD / LZCNT (Leading Zero
        /// Count) on Intel
        abm,
        /// TBM (Trailing Bit Manipulation)
        tbm,
        /// POPCNT (Population Count)
        popcnt,
        /// FXSR (Floating-point context fast save and restor)
        fxsr,
        /// XSAVE (Save Processor Extended States)
        xsave,
        /// XSAVEOPT (Save Processor Extended States Optimized)
        xsaveopt,
        /// XSAVES (Save Processor Extended States Supervisor)
        xsaves,
        /// XSAVEC (Save Processor Extended States Compacted)
        xsavec,
    }

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