如何在Rust中使用__builtin_clzll？

#[cfg(target_arch = "x86_64")]
fn leading_zeros(x: u64) -> u32 {
    let result: u32;
    unsafe {
        asm!("lzcnt $1, $0" : "=r"(result) : "r"(x) : "cc");
    }
    result
}

#[cfg(target_arch = "aarch64")]
fn leading_zeros(x: u64) -> u32 {
    let result: u32;
    unsafe {
        asm!("clz $0, $1" : "=r"(result) : "r"(x) : "cc");
    }
    result
}

fn main() {
    let num: u64 = 42;
    let leading_zeros = leading_zeros(num);
    println!("Number of leading zeros: {}", leading_zeros);
}