abm.rs.html -- source
Description: Source to the Rust file `src/libcore/../stdarch/crates/core_arch/src/x86_64/abm.rs`.
Keywords: rust, rustlang, rust-lang

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    //! Advanced Bit Manipulation (ABM) instructions
    //!
    //! The POPCNT and LZCNT have their own CPUID bits to indicate support.
    //!
    //! The 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].
    //!
    //! [Wikipedia][wikipedia_bmi] provides a quick overview of the instructions
    //! available.
    //!
    //! [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
    //! [wikipedia_bmi]:
    //! https://en.wikipedia.org/wiki/Bit_Manipulation_Instruction_Sets#ABM_.28Advanced_Bit_Manipulation.29

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

    /// Counts the leading most significant zero bits.
    ///
    /// When the operand is zero, it returns its size in bits.
    ///
    /// [Intel's documentation](https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_lzcnt_u64)
    #[inline]
    #[target_feature(enable = "lzcnt")]
    #[cfg_attr(test, assert_instr(lzcnt))]
    #[stable(feature = "simd_x86", since = "1.27.0")]
    pub unsafe fn _lzcnt_u64(x: u64) -> u64 {
        x.leading_zeros() as u64
    }

    /// Counts the bits that are set.
    ///
    /// [Intel's documentation](https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_popcnt64)
    #[inline]
    #[target_feature(enable = "popcnt")]
    #[cfg_attr(test, assert_instr(popcnt))]
    #[stable(feature = "simd_x86", since = "1.27.0")]
    pub unsafe fn _popcnt64(x: i64) -> i32 {
        x.count_ones() as i32
    }

    #[cfg(test)]
    mod tests {
        use stdarch_test::simd_test;

        use crate::core_arch::arch::x86_64::*;

        #[simd_test(enable = "lzcnt")]
        unsafe fn test_lzcnt_u64() {
            assert_eq!(_lzcnt_u64(0b0101_1010), 57);
        }

        #[simd_test(enable = "popcnt")]
        unsafe fn test_popcnt64() {
            assert_eq!(_popcnt64(0b0101_1010), 4);
        }
    }

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