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    //! FXSR floating-point context fast save and restor.

    #[cfg(test)]
    use stdarch_test::assert_instr;

    #[allow(improper_ctypes)]
    extern "C" {
        #[link_name = "llvm.x86.fxsave64"]
        fn fxsave64(p: *mut u8) -> ();
        #[link_name = "llvm.x86.fxrstor64"]
        fn fxrstor64(p: *const u8) -> ();
    }

    /// Saves the `x87` FPU, `MMX` technology, `XMM`, and `MXCSR` registers to the
    /// 512-byte-long 16-byte-aligned memory region `mem_addr`.
    ///
    /// A misaligned destination operand raises a general-protection (#GP) or an
    /// alignment check exception (#AC).
    ///
    /// See [`FXSAVE`][fxsave] and [`FXRSTOR`][fxrstor].
    ///
    /// [fxsave]: http://www.felixcloutier.com/x86/FXSAVE.html
    /// [fxrstor]: http://www.felixcloutier.com/x86/FXRSTOR.html
    ///
    /// [Intel's documentation](https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_fxsave64)
    #[inline]
    #[target_feature(enable = "fxsr")]
    #[cfg_attr(test, assert_instr(fxsave64))]
    #[stable(feature = "simd_x86", since = "1.27.0")]
    pub unsafe fn _fxsave64(mem_addr: *mut u8) {
        fxsave64(mem_addr)
    }

    /// Restores the `XMM`, `MMX`, `MXCSR`, and `x87` FPU registers from the
    /// 512-byte-long 16-byte-aligned memory region `mem_addr`.
    ///
    /// The contents of this memory region should have been written to by a
    /// previous
    /// `_fxsave` or `_fxsave64` intrinsic.
    ///
    /// A misaligned destination operand raises a general-protection (#GP) or an
    /// alignment check exception (#AC).
    ///
    /// See [`FXSAVE`][fxsave] and [`FXRSTOR`][fxrstor].
    ///
    /// [fxsave]: http://www.felixcloutier.com/x86/FXSAVE.html
    /// [fxrstor]: http://www.felixcloutier.com/x86/FXRSTOR.html
    ///
    /// [Intel's documentation](https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_fxrstor64)
    #[inline]
    #[target_feature(enable = "fxsr")]
    #[cfg_attr(test, assert_instr(fxrstor64))]
    #[stable(feature = "simd_x86", since = "1.27.0")]
    pub unsafe fn _fxrstor64(mem_addr: *const u8) {
        fxrstor64(mem_addr)
    }

    #[cfg(test)]
    mod tests {
        use crate::core_arch::x86_64::*;
        use std::{cmp::PartialEq, fmt};
        use stdarch_test::simd_test;

        #[repr(align(16))]
        struct FxsaveArea {
            data: [u8; 512], // 512 bytes
        }

        impl FxsaveArea {
            fn new() -> FxsaveArea {
                FxsaveArea { data: [0; 512] }
            }
            fn ptr(&mut self) -> *mut u8 {
                &mut self.data[0] as *mut _ as *mut u8
            }
        }

        impl PartialEq<FxsaveArea> for FxsaveArea {
            fn eq(&self, other: &FxsaveArea) -> bool {
                for i in 0..self.data.len() {
                    if self.data[i] != other.data[i] {
                        return false;
                    }
                }
                true
            }
        }

        impl fmt::Debug for FxsaveArea {
            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                write!(f, "[")?;
                for i in 0..self.data.len() {
                    write!(f, "{}", self.data[i])?;
                    if i != self.data.len() - 1 {
                        write!(f, ", ")?;
                    }
                }
                write!(f, "]")
            }
        }

        #[simd_test(enable = "fxsr")]
        unsafe fn fxsave64() {
            let mut a = FxsaveArea::new();
            let mut b = FxsaveArea::new();

            fxsr::_fxsave64(a.ptr());
            fxsr::_fxrstor64(a.ptr());
            fxsr::_fxsave64(b.ptr());
            assert_eq!(a, b);
        }
    }