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    //! x86 run-time feature detection is OS independent.

    #[cfg(target_arch = "x86")]
    use crate::arch::x86::*;
    #[cfg(target_arch = "x86_64")]
    use crate::arch::x86_64::*;

    use crate::mem;

    use crate::detect::{Feature, cache, bit};

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

    /// Run-time feature detection on x86 works by using the CPUID instruction.
    ///
    /// The [CPUID Wikipedia page][wiki_cpuid] contains
    /// all the information about which flags to set to query which values, and in
    /// which registers these are reported.
    ///
    /// The definitive references are:
    /// - [Intel 64 and IA-32 Architectures Software Developer's Manual Volume 2:
    ///   Instruction Set Reference, A-Z][intel64_ref].
    /// - [AMD64 Architecture Programmer's Manual, Volume 3: General-Purpose and
    ///   System Instructions][amd64_ref].
    ///
    /// [wiki_cpuid]: https://en.wikipedia.org/wiki/CPUID
    /// [intel64_ref]: http://www.intel.de/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf
    /// [amd64_ref]: http://support.amd.com/TechDocs/24594.pdf
    #[cfg_attr(feature = "cargo-clippy", allow(clippy::similar_names))]
    fn detect_features() -> cache::Initializer {
        let mut value = cache::Initializer::default();

        // If the x86 CPU does not support the CPUID instruction then it is too
        // old to support any of the currently-detectable features.
        if !has_cpuid() {
            return value;
        }

        // Calling `__cpuid`/`__cpuid_count` from here on is safe because the CPU
        // has `cpuid` support.

        // 0. EAX = 0: Basic Information:
        // - EAX returns the "Highest Function Parameter", that is, the maximum
        // leaf value for subsequent calls of `cpuinfo` in range [0,
        // 0x8000_0000]. - The vendor ID is stored in 12 u8 ascii chars,
        // returned in EBX, EDX, and   ECX (in that order):
        let (max_basic_leaf, vendor_id) = unsafe {
            let CpuidResult {
                eax: max_basic_leaf,
                ebx,
                ecx,
                edx,
            } = __cpuid(0);
            let vendor_id: [[u8; 4]; 3] = [
                mem::transmute(ebx),
                mem::transmute(edx),
                mem::transmute(ecx),
            ];
            let vendor_id: [u8; 12] = mem::transmute(vendor_id);
            (max_basic_leaf, vendor_id)
        };

        if max_basic_leaf < 1 {
            // Earlier Intel 486, CPUID not implemented
            return value;
        }

        // EAX = 1, ECX = 0: Queries "Processor Info and Feature Bits";
        // Contains information about most x86 features.
        let CpuidResult {
            ecx: proc_info_ecx,
            edx: proc_info_edx,
            ..
        } = unsafe { __cpuid(0x0000_0001_u32) };

        // EAX = 7, ECX = 0: Queries "Extended Features";
        // Contains information about bmi,bmi2, and avx2 support.
        let (extended_features_ebx, extended_features_ecx) = if max_basic_leaf >= 7
        {
            let CpuidResult { ebx, ecx, .. } = unsafe { __cpuid(0x0000_0007_u32) };
            (ebx, ecx)
        } else {
            (0, 0) // CPUID does not support "Extended Features"
        };

        // EAX = 0x8000_0000, ECX = 0: Get Highest Extended Function Supported
        // - EAX returns the max leaf value for extended information, that is,
        // `cpuid` calls in range [0x8000_0000; u32::MAX]:
        let CpuidResult {
            eax: extended_max_basic_leaf,
            ..
        } = unsafe { __cpuid(0x8000_0000_u32) };

        // EAX = 0x8000_0001, ECX=0: Queries "Extended Processor Info and Feature
        // Bits"
        let extended_proc_info_ecx = if extended_max_basic_leaf >= 1 {
            let CpuidResult { ecx, .. } = unsafe { __cpuid(0x8000_0001_u32) };
            ecx
        } else {
            0
        };

        {
            // borrows value till the end of this scope:
            let mut enable = |r, rb, f| {
                if bit::test(r as usize, rb) {
                    value.set(f as u32);
                }
            };

            enable(proc_info_ecx, 0, Feature::sse3);
            enable(proc_info_ecx, 9, Feature::ssse3);
            enable(proc_info_ecx, 13, Feature::cmpxchg16b);
            enable(proc_info_ecx, 19, Feature::sse4_1);
            enable(proc_info_ecx, 20, Feature::sse4_2);
            enable(proc_info_ecx, 23, Feature::popcnt);
            enable(proc_info_ecx, 25, Feature::aes);
            enable(proc_info_ecx, 1, Feature::pclmulqdq);
            enable(proc_info_ecx, 30, Feature::rdrand);
            enable(extended_features_ebx, 18, Feature::rdseed);
            enable(extended_features_ebx, 19, Feature::adx);
            enable(proc_info_edx, 4, Feature::tsc);
            enable(proc_info_edx, 23, Feature::mmx);
            enable(proc_info_edx, 24, Feature::fxsr);
            enable(proc_info_edx, 25, Feature::sse);
            enable(proc_info_edx, 26, Feature::sse2);
            enable(extended_features_ebx, 29, Feature::sha);

            enable(extended_features_ebx, 3, Feature::bmi);
            enable(extended_features_ebx, 8, Feature::bmi2);

            // `XSAVE` and `AVX` support:
            let cpu_xsave = bit::test(proc_info_ecx as usize, 26);
            if cpu_xsave {
                // 0. Here the CPU supports `XSAVE`.

                // 1. Detect `OSXSAVE`, that is, whether the OS is AVX enabled and
                // supports saving the state of the AVX/AVX2 vector registers on
                // context-switches, see:
                //
                // - [intel: is avx enabled?][is_avx_enabled],
                // - [mozilla: sse.cpp][mozilla_sse_cpp].
                //
                // [is_avx_enabled]: https://software.intel.com/en-us/blogs/2011/04/14/is-avx-enabled
                // [mozilla_sse_cpp]: https://hg.mozilla.org/mozilla-central/file/64bab5cbb9b6/mozglue/build/SSE.cpp#l190
                let cpu_osxsave = bit::test(proc_info_ecx as usize, 27);

                if cpu_osxsave {
                    // 2. The OS must have signaled the CPU that it supports saving and
                    // restoring the:
                    //
                    // * SSE -> `XCR0.SSE[1]`
                    // * AVX -> `XCR0.AVX[2]`
                    // * AVX-512 -> `XCR0.AVX-512[7:5]`.
                    //
                    // by setting the corresponding bits of `XCR0` to `1`.
                    //
                    // This is safe because the CPU supports `xsave`
                    // and the OS has set `osxsave`.
                    let xcr0 = unsafe { _xgetbv(0) };
                    // Test `XCR0.SSE[1]` and `XCR0.AVX[2]` with the mask `0b110 == 6`:
                    let os_avx_support = xcr0 & 6 == 6;
                    // Test `XCR0.AVX-512[7:5]` with the mask `0b1110_0000 == 224`:
                    let os_avx512_support = xcr0 & 224 == 224;

                    // Only if the OS and the CPU support saving/restoring the AVX
                    // registers we enable `xsave` support:
                    if os_avx_support {
                        // See "13.3 ENABLING THE XSAVE FEATURE SET AND XSAVE-ENABLED
                        // FEATURES" in the "Intel® 64 and IA-32 Architectures Software
                        // Developer’s Manual, Volume 1: Basic Architecture":
                        //
                        // "Software enables the XSAVE feature set by setting
                        // CR4.OSXSAVE[bit 18] to 1 (e.g., with the MOV to CR4
                        // instruction). If this bit is 0, execution of any of XGETBV,
                        // XRSTOR, XRSTORS, XSAVE, XSAVEC, XSAVEOPT, XSAVES, and XSETBV
                        // causes an invalid-opcode exception (#UD)"
                        //
                        enable(proc_info_ecx, 26, Feature::xsave);

                        // For `xsaveopt`, `xsavec`, and `xsaves` we need to query:
                        // Processor Extended State Enumeration Sub-leaf (EAX = 0DH,
                        // ECX = 1):
                        if max_basic_leaf >= 0xd {
                            let CpuidResult {
                                eax: proc_extended_state1_eax,
                                ..
                            } = unsafe { __cpuid_count(0xd_u32, 1) };
                            enable(proc_extended_state1_eax, 0, Feature::xsaveopt);
                            enable(proc_extended_state1_eax, 1, Feature::xsavec);
                            enable(proc_extended_state1_eax, 3, Feature::xsaves);
                        }

                        // FMA (uses 256-bit wide registers):
                        enable(proc_info_ecx, 12, Feature::fma);

                        // And AVX/AVX2:
                        enable(proc_info_ecx, 28, Feature::avx);
                        enable(extended_features_ebx, 5, Feature::avx2);

                        // For AVX-512 the OS also needs to support saving/restoring
                        // the extended state, only then we enable AVX-512 support:
                        if os_avx512_support {
                            enable(extended_features_ebx, 16, Feature::avx512f);
                            enable(extended_features_ebx, 17, Feature::avx512dq);
                            enable(extended_features_ebx, 21, Feature::avx512_ifma);
                            enable(extended_features_ebx, 26, Feature::avx512pf);
                            enable(extended_features_ebx, 27, Feature::avx512er);
                            enable(extended_features_ebx, 28, Feature::avx512cd);
                            enable(extended_features_ebx, 30, Feature::avx512bw);
                            enable(extended_features_ebx, 31, Feature::avx512vl);
                            enable(extended_features_ecx, 1, Feature::avx512_vbmi);
                            enable(
                                extended_features_ecx,
                                14,
                                Feature::avx512_vpopcntdq,
                            );
                        }
                    }
                }
            }

            // This detects ABM on AMD CPUs and LZCNT on Intel CPUs.
            // On intel CPUs with popcnt, lzcnt implements the
            // "missing part" of ABM, so we map both to the same
            // internal feature.
            //
            // The `is_x86_feature_detected!("lzcnt")` macro then
            // internally maps to Feature::abm.
            enable(extended_proc_info_ecx, 5, Feature::abm);
            if vendor_id == *b"AuthenticAMD" {
                // These features are only available on AMD CPUs:
                enable(extended_proc_info_ecx, 6, Feature::sse4a);
                enable(extended_proc_info_ecx, 21, Feature::tbm);
            }
        }

        value
    }

    #[cfg(test)]
    mod tests {
        extern crate cupid;

        #[test]
        fn dump() {
            println!("aes: {:?}", is_x86_feature_detected!("aes"));
            println!("pclmulqdq: {:?}", is_x86_feature_detected!("pclmulqdq"));
            println!("rdrand: {:?}", is_x86_feature_detected!("rdrand"));
            println!("rdseed: {:?}", is_x86_feature_detected!("rdseed"));
            println!("tsc: {:?}", is_x86_feature_detected!("tsc"));
            println!("sse: {:?}", is_x86_feature_detected!("sse"));
            println!("sse2: {:?}", is_x86_feature_detected!("sse2"));
            println!("sse3: {:?}", is_x86_feature_detected!("sse3"));
            println!("ssse3: {:?}", is_x86_feature_detected!("ssse3"));
            println!("sse4.1: {:?}", is_x86_feature_detected!("sse4.1"));
            println!("sse4.2: {:?}", is_x86_feature_detected!("sse4.2"));
            println!("sse4a: {:?}", is_x86_feature_detected!("sse4a"));
            println!("sha: {:?}", is_x86_feature_detected!("sha"));
            println!("avx: {:?}", is_x86_feature_detected!("avx"));
            println!("avx2: {:?}", is_x86_feature_detected!("avx2"));
            println!("avx512f {:?}", is_x86_feature_detected!("avx512f"));
            println!("avx512cd {:?}", is_x86_feature_detected!("avx512cd"));
            println!("avx512er {:?}", is_x86_feature_detected!("avx512er"));
            println!("avx512pf {:?}", is_x86_feature_detected!("avx512pf"));
            println!("avx512bw {:?}", is_x86_feature_detected!("avx512bw"));
            println!("avx512dq {:?}", is_x86_feature_detected!("avx512dq"));
            println!("avx512vl {:?}", is_x86_feature_detected!("avx512vl"));
            println!("avx512_ifma {:?}", is_x86_feature_detected!("avx512ifma"));
            println!("avx512_vbmi {:?}", is_x86_feature_detected!("avx512vbmi"));
            println!(
                "avx512_vpopcntdq {:?}",
                is_x86_feature_detected!("avx512vpopcntdq")
            );
            println!("fma: {:?}", is_x86_feature_detected!("fma"));
            println!("abm: {:?}", is_x86_feature_detected!("abm"));
            println!("bmi: {:?}", is_x86_feature_detected!("bmi1"));
            println!("bmi2: {:?}", is_x86_feature_detected!("bmi2"));
            println!("tbm: {:?}", is_x86_feature_detected!("tbm"));
            println!("popcnt: {:?}", is_x86_feature_detected!("popcnt"));
            println!("lzcnt: {:?}", is_x86_feature_detected!("lzcnt"));
            println!("fxsr: {:?}", is_x86_feature_detected!("fxsr"));
            println!("xsave: {:?}", is_x86_feature_detected!("xsave"));
            println!("xsaveopt: {:?}", is_x86_feature_detected!("xsaveopt"));
            println!("xsaves: {:?}", is_x86_feature_detected!("xsaves"));
            println!("xsavec: {:?}", is_x86_feature_detected!("xsavec"));
            println!("cmpxchg16b: {:?}", is_x86_feature_detected!("cmpxchg16b"));
            println!("adx: {:?}", is_x86_feature_detected!("adx"));
        }

        #[test]
        fn compare_with_cupid() {
            let information = cupid::master().unwrap();
            assert_eq!(is_x86_feature_detected!("aes"), information.aesni());
            assert_eq!(is_x86_feature_detected!("pclmulqdq"), information.pclmulqdq());
            assert_eq!(is_x86_feature_detected!("rdrand"), information.rdrand());
            assert_eq!(is_x86_feature_detected!("rdseed"), information.rdseed());
            assert_eq!(is_x86_feature_detected!("tsc"), information.tsc());
            assert_eq!(is_x86_feature_detected!("sse"), information.sse());
            assert_eq!(is_x86_feature_detected!("sse2"), information.sse2());
            assert_eq!(is_x86_feature_detected!("sse3"), information.sse3());
            assert_eq!(is_x86_feature_detected!("ssse3"), information.ssse3());
            assert_eq!(is_x86_feature_detected!("sse4.1"), information.sse4_1());
            assert_eq!(is_x86_feature_detected!("sse4.2"), information.sse4_2());
            assert_eq!(is_x86_feature_detected!("sse4a"), information.sse4a());
            assert_eq!(is_x86_feature_detected!("sha"), information.sha());
            assert_eq!(is_x86_feature_detected!("avx"), information.avx());
            assert_eq!(is_x86_feature_detected!("avx2"), information.avx2());
            assert_eq!(is_x86_feature_detected!("avx512f"), information.avx512f());
            assert_eq!(is_x86_feature_detected!("avx512cd"), information.avx512cd());
            assert_eq!(is_x86_feature_detected!("avx512er"), information.avx512er());
            assert_eq!(is_x86_feature_detected!("avx512pf"), information.avx512pf());
            assert_eq!(is_x86_feature_detected!("avx512bw"), information.avx512bw());
            assert_eq!(is_x86_feature_detected!("avx512dq"), information.avx512dq());
            assert_eq!(is_x86_feature_detected!("avx512vl"), information.avx512vl());
            assert_eq!(
                is_x86_feature_detected!("avx512ifma"),
                information.avx512_ifma()
            );
            assert_eq!(
                is_x86_feature_detected!("avx512vbmi"),
                information.avx512_vbmi()
            );
            assert_eq!(
                is_x86_feature_detected!("avx512vpopcntdq"),
                information.avx512_vpopcntdq()
            );
            assert_eq!(is_x86_feature_detected!("fma"), information.fma());
            assert_eq!(is_x86_feature_detected!("bmi1"), information.bmi1());
            assert_eq!(is_x86_feature_detected!("bmi2"), information.bmi2());
            assert_eq!(is_x86_feature_detected!("popcnt"), information.popcnt());
            assert_eq!(is_x86_feature_detected!("abm"), information.lzcnt());
            assert_eq!(is_x86_feature_detected!("tbm"), information.tbm());
            assert_eq!(is_x86_feature_detected!("lzcnt"), information.lzcnt());
            assert_eq!(is_x86_feature_detected!("xsave"), information.xsave());
            assert_eq!(is_x86_feature_detected!("xsaveopt"), information.xsaveopt());
            assert_eq!(
                is_x86_feature_detected!("xsavec"),
                information.xsavec_and_xrstor()
            );
            assert_eq!(
                is_x86_feature_detected!("xsaves"),
                information.xsaves_xrstors_and_ia32_xss()
            );
            assert_eq!(
                is_x86_feature_detected!("cmpxchg16b"),
                information.cmpxchg16b(),
            );
            assert_eq!(
                is_x86_feature_detected!("adx"),
                information.adx(),
            );
        }
    }

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