You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.rs
    path of file: ./repos/sightglass/benchmarks/hex-simd/rust-benchmark/src
    
    the code of the file until where you have to start completion: use sightglass_api as bench;
use std::io::{self, Read};
use std::str;

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

fn main() {
    let input = std::fs::read("./default.input").unwrap();
    let mut dst = vec![0; 2 * input.len()];
    bench::start();
    let s = hex_encode(&input, &mut dst).unwrap();
    bench::end();
    println!("{s}");
}

fn hex_encode<'a>(src: &[u8], dst: &'a mut [u8]) -> Result<&'a str, usize> {
    let len = src.len().checked_mul(2).unwrap();
    if dst.len() < len {
        return Err(len);
    }

    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
    {
        if is_x86_feature_detected!("avx2") {
            return unsafe { hex_encode_avx2(src, dst) };
        }
        if is_x86_feature_detected!("sse4.1") {
            return unsafe { hex_encode_sse41(src, dst) };
        }
    }
    #[cfg(target_arch = "wasm32")]
    {
        if true {
            return unsafe { hex_encode_simd128(src, dst) };
        }
    }

    hex_encode_fallback(src, dst)
}

#[target_feature(enable = "avx2")]
#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
unsafe fn hex_encode_avx2<'a>(mut src: &[u8], dst: &'a mut [u8]) -> Result<&'a str, usize> {
    let ascii_zero = _mm256_set1_epi8(b'0' as i8);
    let nines = _mm256_set1_epi8(9);
    let a
    
unsafe fn hex_encode_avx2<'a>(mut src: &[u8], dst: &'a mut [u8]) -> Result<&'a str, usize> {
    let ascii_zero = _mm256_set1_epi8(b'0' as i8);
    let nines = _mm256_set1_epi8(9);
    let ascii_a = _mm256_set1_epi8((b'a' - 9 - 1) as i8);
    let and4bits = _mm256_set1_epi8(0xf);

    let mut i = 0_usize;
    while src.len() >= 32 {
        let invec = _mm256_loadu_si256(src.as_ptr() as *const _);

        let masked1 = _mm256_and_si256(invec, and4bits);
        let masked2 = _mm256_and_si256(_mm256_srli_epi64(invec, 4), and4bits);

        // return 0xff corresponding to the elements > 9, or 0x00 otherwise
        let cmpmask1 = _mm256_cmpgt_epi8(masked1, nines);
        let cmpmask2 = _mm256_cmpgt_epi8(masked2, nines);

        // add '0' or the offset depending on the masks
        let masked1 = _mm256_add_epi8(masked1, _mm256_blendv_epi8(ascii_zero, ascii_a, cmpmask1));
        let masked2 = _mm256_add_epi8(masked2, _mm256_blendv_epi8(ascii_zero, ascii_a, cmpmask2));

        // interleave masked1 and masked2 bytes
        let res1 = _mm256_unpacklo_epi8(masked2, masked1);
        let res2 = _mm256_unpackhi_epi8(masked2, masked1);

        // Store everything into the right destination now
        let base = dst.as_mut_ptr().add(i * 2);
        let base1 = base.add(0) as *mut _;
        let base2 = base.add(16) as *mut _;
        let base3 = base.add(32) as *mut _;
        let base4 = base.add(48) as *mut _;
        _mm256_storeu2_m128i(base3, base1, res1);
        _mm256_storeu2_m128i(base4, base2, res2);
        src = &src[32..];
        i += 32;
    }

    let _ = hex_encode_sse41(src, &mut dst[i * 2..]);

    Ok(str::from_utf8_unchecked(&dst[..src.len() * 2 + i * 2]))
}