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    //! ARMv8 intrinsics.
    //!
    //! The reference is [ARMv8-A Reference Manual][armv8].
    //!
    //! [armv8]: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.
    //! ddi0487a.k_10775/index.html

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

    /// Reverse the order of the bytes.
    #[inline]
    #[cfg_attr(test, assert_instr(rev))]
    pub unsafe fn _rev_u64(x: u64) -> u64 {
        x.swap_bytes() as u64
    }

    /// Count Leading Zeros.
    #[inline]
    #[cfg_attr(test, assert_instr(clz))]
    pub unsafe fn _clz_u64(x: u64) -> u64 {
        x.leading_zeros() as u64
    }

    /// Reverse the bit order.
    #[inline]
    #[cfg_attr(test, assert_instr(rbit))]
    pub unsafe fn _rbit_u64(x: u64) -> u64 {
        use intrinsics::bitreverse;
        bitreverse(x)
    }

    /// Counts the leading most significant bits set.
    ///
    /// When all bits of the operand are set it returns the size of the operand in
    /// bits.
    #[inline]
    #[cfg_attr(test, assert_instr(cls))]
    pub unsafe fn _cls_u32(x: u32) -> u32 {
        u32::leading_zeros((((((x as i32) >> 31) as u32) ^ x) << 1) | 1) as u32
    }

    /// Counts the leading most significant bits set.
    ///
    /// When all bits of the operand are set it returns the size of the operand in
    /// bits.
    #[inline]
    #[cfg_attr(test, assert_instr(cls))]
    pub unsafe fn _cls_u64(x: u64) -> u64 {
        u64::leading_zeros((((((x as i64) >> 63) as u64) ^ x) << 1) | 1) as u64
    }

    #[cfg(test)]
    mod tests {
        use core_arch::aarch64::v8;

        #[test]
        fn _rev_u64() {
            unsafe {
                assert_eq!(
                    v8::_rev_u64(0b0000_0000_1111_1111_0000_0000_1111_1111_u64),
                    0b1111_1111_0000_0000_1111_1111_0000_0000_0000_0000_0000_0000_0000_0000_0000_0000_u64
                );
            }
        }

        #[test]
        fn _clz_u64() {
            unsafe {
                assert_eq!(v8::_clz_u64(0b0000_1010u64), 60u64);
            }
        }

        #[test]
        fn _rbit_u64() {
            unsafe {
                assert_eq!(
                    v8::_rbit_u64(0b0000_0000_1111_1101_0000_0000_1111_1111_u64),
                    0b1111_1111_0000_0000_1011_1111_0000_0000_0000_0000_0000_0000_0000_0000_0000_0000_u64
                );
            }
        }

        #[test]
        fn _cls_u32() {
            unsafe {
                assert_eq!(
                    v8::_cls_u32(0b1111_1111_1111_1111_0000_0000_1111_1111_u32),
                    15_u32
                );
            }
        }

        #[test]
        fn _cls_u64() {
            unsafe {
                assert_eq!(
                    v8::_cls_u64(
                        0b1111_1111_1111_1111_0000_0000_1111_1111_0000_0000_0000_0000_0000_0000_0000_0000_u64
                    ),
                    15_u64
                );
            }
        }
    }

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