rustfs-erasure-codec 7.0.1

use std::env;
use std::fs::File;
use std::io::Write;
use std::path::Path;

#[cfg(any(
    feature = "simd-neon",
    feature = "simd-ssse3",
    feature = "simd-avx2",
    feature = "simd-avx512",
    feature = "simd-gfni",
    feature = "simd-vsx",
))]
extern crate cc;

const FIELD_SIZE: usize = 256;

const GENERATING_POLYNOMIAL: usize = 29;

#[cfg(any(
    feature = "simd-neon",
    feature = "simd-ssse3",
    feature = "simd-avx2",
    feature = "simd-avx512",
    feature = "simd-gfni",
    feature = "simd-vsx",
))]
#[derive(Copy, Clone)]
enum SimdCBuildTarget {
    Baseline,
    ExplicitArch,
}

fn gen_log_table(polynomial: usize) -> [u8; FIELD_SIZE] {
    let mut result: [u8; FIELD_SIZE] = [0; FIELD_SIZE];
    let mut b: usize = 1;

    for log in 0..FIELD_SIZE - 1 {
        result[b] = log as u8;

        b <<= 1;

        if FIELD_SIZE <= b {
            b = (b - FIELD_SIZE) ^ polynomial;
        }
    }

    result
}

const EXP_TABLE_SIZE: usize = FIELD_SIZE * 2 - 2;

fn gen_exp_table(log_table: &[u8; FIELD_SIZE]) -> [u8; EXP_TABLE_SIZE] {
    let mut result: [u8; EXP_TABLE_SIZE] = [0; EXP_TABLE_SIZE];

    for (i, &log_entry) in log_table.iter().enumerate().skip(1) {
        let log = log_entry as usize;
        result[log] = i as u8;
        result[log + FIELD_SIZE - 1] = i as u8;
    }

    result
}

fn multiply(log_table: &[u8; FIELD_SIZE], exp_table: &[u8; EXP_TABLE_SIZE], a: u8, b: u8) -> u8 {
    if a == 0 || b == 0 {
        0
    } else {
        let log_a = log_table[a as usize];
        let log_b = log_table[b as usize];
        let log_result = log_a as usize + log_b as usize;
        exp_table[log_result]
    }
}

fn gen_mul_table(
    log_table: &[u8; FIELD_SIZE],
    exp_table: &[u8; EXP_TABLE_SIZE],
) -> [[u8; FIELD_SIZE]; FIELD_SIZE] {
    let mut result: [[u8; FIELD_SIZE]; FIELD_SIZE] = [[0; 256]; 256];

    for (a, row) in result.iter_mut().enumerate() {
        for (b, cell) in row.iter_mut().enumerate() {
            *cell = multiply(log_table, exp_table, a as u8, b as u8);
        }
    }

    result
}

fn gen_mul_table_half(
    log_table: &[u8; FIELD_SIZE],
    exp_table: &[u8; EXP_TABLE_SIZE],
) -> ([[u8; 16]; FIELD_SIZE], [[u8; 16]; FIELD_SIZE]) {
    let mut low: [[u8; 16]; FIELD_SIZE] = [[0; 16]; FIELD_SIZE];
    let mut high: [[u8; 16]; FIELD_SIZE] = [[0; 16]; FIELD_SIZE];

    for a in 0..low.len() {
        for b in 0..low.len() {
            let mut result = 0;
            if !(a == 0 || b == 0) {
                let log_a = log_table[a];
                let log_b = log_table[b];
                result = exp_table[log_a as usize + log_b as usize];
            }
            if (b & 0x0F) == b {
                low[a][b] = result;
            }
            if (b & 0xF0) == b {
                high[a][b >> 4] = result;
            }
        }
    }
    (low, high)
}

macro_rules! write_table {
    (1D => $file:ident, $table:ident, $name:expr, $type:expr) => {{
        let len = $table.len();
        let mut table_str = String::from(format!("pub static {}: [{}; {}] = [", $name, $type, len));

        for v in $table.iter() {
            let str = format!("{}, ", v);
            table_str.push_str(&str);
        }

        table_str.push_str("];\n");

        $file.write_all(table_str.as_bytes()).unwrap();
    }};
    (2D => $file:ident, $table:ident, $name:expr, $type:expr) => {{
        let rows = $table.len();
        let cols = $table[0].len();
        let mut table_str = String::from(format!(
            "pub static {}: [[{}; {}]; {}] = [",
            $name, $type, cols, rows
        ));

        for a in $table.iter() {
            table_str.push_str("[");
            for b in a.iter() {
                let str = format!("{}, ", b);
                table_str.push_str(&str);
            }
            table_str.push_str("],\n");
        }

        table_str.push_str("];\n");

        $file.write_all(table_str.as_bytes()).unwrap();
    }};
}

fn write_tables() {
    let log_table = gen_log_table(GENERATING_POLYNOMIAL);
    let exp_table = gen_exp_table(&log_table);
    let mul_table = gen_mul_table(&log_table, &exp_table);

    let out_dir = env::var("OUT_DIR").unwrap();
    let dest_path = Path::new(&out_dir).join("table.rs");
    let mut f = File::create(&dest_path).unwrap();

    write_table!(1D => f, log_table,      "LOG_TABLE",      "u8");
    write_table!(1D => f, exp_table,      "EXP_TABLE",      "u8");
    write_table!(2D => f, mul_table,      "MUL_TABLE",      "u8");

    if cfg!(any(
        feature = "simd-neon",
        feature = "simd-ssse3",
        feature = "simd-avx2",
        feature = "simd-avx512",
        feature = "simd-gfni",
        feature = "simd-vsx"
    )) {
        let (mul_table_low, mul_table_high) = gen_mul_table_half(&log_table, &exp_table);

        write_table!(2D => f, mul_table_low,  "MUL_TABLE_LOW",  "u8");
        write_table!(2D => f, mul_table_high, "MUL_TABLE_HIGH", "u8");
    }
}

#[cfg(any(
    feature = "simd-neon",
    feature = "simd-ssse3",
    feature = "simd-avx2",
    feature = "simd-avx512",
    feature = "simd-gfni"
))]
fn target_cfg(name: &str) -> String {
    env::var(name).unwrap_or_default()
}

#[cfg(any(
    feature = "simd-neon",
    feature = "simd-ssse3",
    feature = "simd-avx2",
    feature = "simd-avx512",
    feature = "simd-gfni"
))]
fn should_compile_simd_c_for_target() -> bool {
    let target_arch = target_cfg("CARGO_CFG_TARGET_ARCH");
    let target_env = target_cfg("CARGO_CFG_TARGET_ENV");
    let target_os = target_cfg("CARGO_CFG_TARGET_OS");

    let arch_supported = matches!(target_arch.as_str(), "x86_64" | "aarch64" | "powerpc64");
    let env_supported = target_env != "msvc";
    let os_supported = !matches!(target_os.as_str(), "android" | "ios");

    arch_supported && env_supported && os_supported
}

#[cfg(any(
    feature = "simd-neon",
    feature = "simd-ssse3",
    feature = "simd-avx2",
    feature = "simd-avx512",
    feature = "simd-gfni"
))]
fn is_valid_march_value(arch: &str) -> bool {
    !arch.is_empty()
        && arch
            .bytes()
            .all(|b| b.is_ascii_alphanumeric() || matches!(b, b'_' | b'-' | b'.' | b'+'))
}

#[cfg(any(
    feature = "simd-neon",
    feature = "simd-ssse3",
    feature = "simd-avx2",
    feature = "simd-avx512",
    feature = "simd-gfni"
))]
fn compile_simd_c() {
    if !should_compile_simd_c_for_target() {
        if let Ok(arch) = env::var("RUST_REED_SOLOMON_ERASURE_ARCH") {
            println!(
                "cargo:warning=ignoring RUST_REED_SOLOMON_ERASURE_ARCH={arch} because simd-c is disabled for this target"
            );
        }
        return;
    }

    let mut build = cc::Build::new();
    build.opt_level(3);

    let mut build_target = SimdCBuildTarget::Baseline;

    match env::var("RUST_REED_SOLOMON_ERASURE_ARCH") {
        Ok(arch) => {
            if is_valid_march_value(&arch) {
                // Use explicitly specified environment variable as architecture.
                build.flag(format!("-march={arch}"));
                println!("cargo:rustc-env=RSE_SIMD_C_ARCH={arch}");
                println!("cargo:rustc-cfg=rse_simd_c_build_unknown");
                build_target = SimdCBuildTarget::ExplicitArch;
            } else {
                println!(
                    "cargo:warning=invalid RUST_REED_SOLOMON_ERASURE_ARCH value '{arch}', expected [A-Za-z0-9_.+-]+; falling back to baseline simd-c build"
                );
            }
        }
        Err(_error) => {}
    }

    match build_target {
        SimdCBuildTarget::Baseline => {
            println!("cargo:rustc-cfg=rse_simd_c_build_baseline");
            println!("cargo:rustc-env=RSE_SIMD_C_ARCH=baseline");
        }
        SimdCBuildTarget::ExplicitArch => {}
    }

    build
        .flag("-std=c11")
        .file("simd_c/reedsolomon.c")
        .compile("reedsolomon");
}

#[cfg(not(any(
    feature = "simd-neon",
    feature = "simd-ssse3",
    feature = "simd-avx2",
    feature = "simd-avx512",
    feature = "simd-gfni",
    feature = "simd-vsx"
)))]
fn compile_simd_c() {}

/// Generate specialized encode functions for common (data_shards, parity_shards) configurations.
///
/// These functions unroll the data shard loop and inline the GF multiplication,
/// eliminating per-shard function pointer dispatch and enabling better register allocation.
fn generate_encode_codegen() {
    let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap_or_default();

    // Only generate for x86_64 (AVX2) and aarch64 (NEON)
    if target_arch != "x86_64" && target_arch != "aarch64" {
        return;
    }

    let out_dir = env::var("OUT_DIR").unwrap();
    let dest_path = Path::new(&out_dir).join("codegen_encode.rs");
    let mut f = File::create(&dest_path).unwrap();

    // Common configurations from MinIO, Ceph, HDFS
    let configs: &[(usize, usize)] = &[(10, 4), (12, 4), (8, 3), (8, 4), (6, 3), (4, 2)];

    if target_arch == "x86_64" {
        generate_encode_codegen_avx2(&mut f, configs);
    } else if target_arch == "aarch64" {
        generate_encode_codegen_neon(&mut f, configs);
    }
}

fn generate_encode_codegen_avx2(f: &mut File, configs: &[(usize, usize)]) {
    use std::io::Write;

    writeln!(
        f,
        "// Auto-generated AVX2 encode functions for common configurations."
    )
    .unwrap();
    writeln!(f, "// Generated by build.rs — do not edit manually.").unwrap();
    writeln!(f).unwrap();
    writeln!(f, "#[cfg(all(").unwrap();
    writeln!(f, "    feature = \"simd-avx2\",").unwrap();
    writeln!(f, "    target_arch = \"x86_64\",").unwrap();
    writeln!(f, "    not(target_env = \"msvc\"),").unwrap();
    writeln!(
        f,
        "    not(any(target_os = \"android\", target_os = \"ios\"))"
    )
    .unwrap();
    writeln!(f, "))]").unwrap();
    writeln!(f, "mod avx2_impl {{").unwrap();
    writeln!(f, "    use core::arch::x86_64::*;").unwrap();
    writeln!(f).unwrap();

    for &(d, p) in configs {
        generate_encode_fn_avx2(f, d, p);
    }

    writeln!(f, "}}").unwrap();
    writeln!(f).unwrap();

    // Re-export dispatch function at the module level
    writeln!(f, "#[cfg(all(").unwrap();
    writeln!(f, "    feature = \"simd-avx2\",").unwrap();
    writeln!(f, "    target_arch = \"x86_64\",").unwrap();
    writeln!(f, "    not(target_env = \"msvc\"),").unwrap();
    writeln!(
        f,
        "    not(any(target_os = \"android\", target_os = \"ios\"))"
    )
    .unwrap();
    writeln!(f, "))]").unwrap();
    writeln!(f, "pub(crate) fn try_encode_codegen_avx2(").unwrap();
    writeln!(f, "    data_shard_count: usize,").unwrap();
    writeln!(f, "    parity_shard_count: usize,").unwrap();
    writeln!(f, "    parity_rows: &[&[u8]],").unwrap();
    writeln!(f, "    data: &[&[u8]],").unwrap();
    writeln!(f, "    parity: &mut [&mut [u8]],").unwrap();
    writeln!(f, "    shard_len: usize,").unwrap();
    writeln!(f, ") -> bool {{").unwrap();
    writeln!(f, "    match (data_shard_count, parity_shard_count) {{").unwrap();
    for &(d, p) in configs {
        writeln!(f, "        ({d}, {p}) => unsafe {{").unwrap();
        writeln!(
            f,
            "            avx2_impl::encode_{d}x{p}_avx2(parity_rows, data, parity, shard_len);"
        )
        .unwrap();
        writeln!(f, "            true").unwrap();
        writeln!(f, "        }},").unwrap();
    }
    writeln!(f, "        _ => false,").unwrap();
    writeln!(f, "    }}").unwrap();
    writeln!(f, "}}").unwrap();
}

fn generate_encode_fn_avx2(f: &mut File, d: usize, p: usize) {
    use std::io::Write;

    writeln!(
        f,
        "    /// Specialized encode for {d} data + {p} parity shards using AVX2."
    )
    .unwrap();
    writeln!(f, "    ///").unwrap();
    writeln!(f, "    /// # Safety").unwrap();
    writeln!(f, "    ///").unwrap();
    writeln!(
        f,
        "    /// Caller must ensure AVX2 is available and all slices have length >= shard_len."
    )
    .unwrap();
    writeln!(f, "    #[target_feature(enable = \"avx2\")]").unwrap();
    writeln!(f, "    pub(super) unsafe fn encode_{d}x{p}_avx2(").unwrap();
    writeln!(f, "        parity_rows: &[&[u8]],").unwrap();
    writeln!(f, "        data: &[&[u8]],").unwrap();
    writeln!(f, "        parity: &mut [&mut [u8]],").unwrap();
    writeln!(f, "        shard_len: usize,").unwrap();
    writeln!(f, "    ) {{").unwrap();
    writeln!(f, "        unsafe {{").unwrap();

    writeln!(
        f,
        "        let nibble_mask: __m256i = _mm256_set1_epi8(0x0f);"
    )
    .unwrap();

    // Load coefficient tables for each (parity_row, data_shard) pair
    writeln!(
        f,
        "        // Load GF multiplication table halves for all coefficients."
    )
    .unwrap();
    writeln!(
        f,
        "        // Layout: coef_tables[p_idx][d_idx] = (low_tbl, high_tbl)"
    )
    .unwrap();
    for pi in 0..p {
        for di in 0..d {
            writeln!(
                f,
                "        let (coef_low_{pi}_{di}, coef_high_{pi}_{di}): (__m256i, __m256i) = {{"
            )
            .unwrap();
            writeln!(f, "            let c = parity_rows[{pi}][{di}];").unwrap();
            writeln!(
                f,
                "            let (lh, hh) = super::super::load_table_halves(c);"
            )
            .unwrap();
            writeln!(
                f,
                "            let low128: __m128i = _mm_loadu_si128(lh.as_ptr().cast());"
            )
            .unwrap();
            writeln!(
                f,
                "            let high128: __m128i = _mm_loadu_si128(hh.as_ptr().cast());"
            )
            .unwrap();
            writeln!(f, "            (_mm256_broadcastsi128_si256(low128), _mm256_broadcastsi128_si256(high128))").unwrap();
            writeln!(f, "        }};").unwrap();
        }
    }

    writeln!(f).unwrap();
    writeln!(f, "        let bytes_done = shard_len & !31usize;").unwrap();
    writeln!(f).unwrap();
    writeln!(
        f,
        "        // Main SIMD loop: process 32 bytes per iteration."
    )
    .unwrap();
    writeln!(f, "        let mut offset = 0usize;").unwrap();
    writeln!(f, "        while offset < bytes_done {{").unwrap();

    // Load all data shards
    writeln!(f, "            // Load all {d} data shards.").unwrap();
    for di in 0..d {
        writeln!(f, "            let d{di}: __m256i = _mm256_loadu_si256(data[{di}][offset..].as_ptr().cast());").unwrap();
    }

    writeln!(f).unwrap();

    // Compute each parity shard
    for pi in 0..p {
        writeln!(f, "            // Compute parity shard {pi}.").unwrap();
        // For first data shard: direct multiply (no XOR accumulation)
        writeln!(
            f,
            "            let low = _mm256_and_si256(d0, nibble_mask);"
        )
        .unwrap();
        writeln!(
            f,
            "            let high = _mm256_and_si256(_mm256_srli_epi64::<4>(d0), nibble_mask);"
        )
        .unwrap();
        writeln!(
            f,
            "            let mut acc_{pi}: __m256i = _mm256_xor_si256("
        )
        .unwrap();
        writeln!(
            f,
            "                _mm256_shuffle_epi8(coef_low_{pi}_0, low),"
        )
        .unwrap();
        writeln!(
            f,
            "                _mm256_shuffle_epi8(coef_high_{pi}_0, high),"
        )
        .unwrap();
        writeln!(f, "            );").unwrap();

        // For remaining data shards: XOR accumulate
        for di in 1..d {
            writeln!(
                f,
                "            let low = _mm256_and_si256(d{di}, nibble_mask);"
            )
            .unwrap();
            writeln!(f, "            let high = _mm256_and_si256(_mm256_srli_epi64::<4>(d{di}), nibble_mask);").unwrap();
            writeln!(
                f,
                "            acc_{pi} = _mm256_xor_si256(acc_{pi}, _mm256_xor_si256("
            )
            .unwrap();
            writeln!(
                f,
                "                _mm256_shuffle_epi8(coef_low_{pi}_{di}, low),"
            )
            .unwrap();
            writeln!(
                f,
                "                _mm256_shuffle_epi8(coef_high_{pi}_{di}, high),"
            )
            .unwrap();
            writeln!(f, "            ));").unwrap();
        }

        writeln!(
            f,
            "            _mm256_storeu_si256(parity[{pi}][offset..].as_mut_ptr().cast(), acc_{pi});"
        )
        .unwrap();
    }

    writeln!(f, "            offset += 32;").unwrap();
    writeln!(f, "        }}").unwrap();

    // Scalar tail
    writeln!(f).unwrap();
    writeln!(f, "        // Scalar tail for remaining bytes.").unwrap();
    writeln!(f, "        for i in bytes_done..shard_len {{").unwrap();
    for pi in 0..p {
        writeln!(f, "            let mut acc: u8 = 0;").unwrap();
        for di in 0..d {
            writeln!(f, "            acc ^= super::super::super::MUL_TABLE[parity_rows[{pi}][{di}] as usize][data[{di}][i] as usize];").unwrap();
        }
        writeln!(f, "            parity[{pi}][i] = acc;").unwrap();
    }
    writeln!(f, "        }}").unwrap();

    writeln!(f, "        }}").unwrap();
    writeln!(f, "    }}").unwrap();
    writeln!(f).unwrap();
}

fn generate_encode_codegen_neon(f: &mut File, configs: &[(usize, usize)]) {
    use std::io::Write;

    writeln!(
        f,
        "// Auto-generated NEON encode functions for common configurations."
    )
    .unwrap();
    writeln!(f, "// Generated by build.rs — do not edit manually.").unwrap();
    writeln!(f).unwrap();
    writeln!(f, "#[cfg(all(").unwrap();
    writeln!(f, "    feature = \"simd-neon\",").unwrap();
    writeln!(f, "    target_arch = \"aarch64\",").unwrap();
    writeln!(f, "    not(target_env = \"msvc\"),").unwrap();
    writeln!(
        f,
        "    not(any(target_os = \"android\", target_os = \"ios\"))"
    )
    .unwrap();
    writeln!(f, "))]").unwrap();
    writeln!(f, "mod neon_impl {{").unwrap();
    writeln!(f, "    use core::arch::aarch64::*;").unwrap();
    writeln!(f).unwrap();

    for &(d, p) in configs {
        generate_encode_fn_neon(f, d, p);
    }

    writeln!(f, "}}").unwrap();
    writeln!(f).unwrap();

    // Re-export dispatch function
    writeln!(f, "#[cfg(all(").unwrap();
    writeln!(f, "    feature = \"simd-neon\",").unwrap();
    writeln!(f, "    target_arch = \"aarch64\",").unwrap();
    writeln!(f, "    not(target_env = \"msvc\"),").unwrap();
    writeln!(
        f,
        "    not(any(target_os = \"android\", target_os = \"ios\"))"
    )
    .unwrap();
    writeln!(f, "))]").unwrap();
    writeln!(f, "pub(crate) fn try_encode_codegen_neon(").unwrap();
    writeln!(f, "    data_shard_count: usize,").unwrap();
    writeln!(f, "    parity_shard_count: usize,").unwrap();
    writeln!(f, "    parity_rows: &[&[u8]],").unwrap();
    writeln!(f, "    data: &[&[u8]],").unwrap();
    writeln!(f, "    parity: &mut [&mut [u8]],").unwrap();
    writeln!(f, "    shard_len: usize,").unwrap();
    writeln!(f, ") -> bool {{").unwrap();
    writeln!(f, "    match (data_shard_count, parity_shard_count) {{").unwrap();
    for &(d, p) in configs {
        writeln!(f, "        ({d}, {p}) => unsafe {{").unwrap();
        writeln!(
            f,
            "            neon_impl::encode_{d}x{p}_neon(parity_rows, data, parity, shard_len);"
        )
        .unwrap();
        writeln!(f, "            true").unwrap();
        writeln!(f, "        }},").unwrap();
    }
    writeln!(f, "        _ => false,").unwrap();
    writeln!(f, "    }}").unwrap();
    writeln!(f, "}}").unwrap();
}

fn generate_encode_fn_neon(f: &mut File, d: usize, p: usize) {
    use std::io::Write;

    writeln!(
        f,
        "    /// Specialized encode for {d} data + {p} parity shards using NEON."
    )
    .unwrap();
    writeln!(f, "    ///").unwrap();
    writeln!(f, "    /// # Safety").unwrap();
    writeln!(f, "    ///").unwrap();
    writeln!(
        f,
        "    /// Caller must ensure NEON is available and all slices have length >= shard_len."
    )
    .unwrap();
    writeln!(f, "    #[target_feature(enable = \"neon\")]").unwrap();
    writeln!(f, "    pub(super) unsafe fn encode_{d}x{p}_neon(").unwrap();
    writeln!(f, "        parity_rows: &[&[u8]],").unwrap();
    writeln!(f, "        data: &[&[u8]],").unwrap();
    writeln!(f, "        parity: &mut [&mut [u8]],").unwrap();
    writeln!(f, "        shard_len: usize,").unwrap();
    writeln!(f, "    ) {{").unwrap();

    writeln!(f, "        let nibble_mask: uint8x16_t = vdupq_n_u8(0x0f);").unwrap();

    // Load coefficient tables
    writeln!(
        f,
        "        // Load GF multiplication table halves for all coefficients."
    )
    .unwrap();
    for pi in 0..p {
        for di in 0..d {
            writeln!(f, "        let (coef_low_{pi}_{di}, coef_high_{pi}_{di}): (uint8x16_t, uint8x16_t) = unsafe {{").unwrap();
            writeln!(f, "            let c = parity_rows[{pi}][{di}];").unwrap();
            writeln!(
                f,
                "            (vld1q_u8(super::super::super::MUL_TABLE_LOW[c as usize].as_ptr()),"
            )
            .unwrap();
            writeln!(
                f,
                "             vld1q_u8(super::super::super::MUL_TABLE_HIGH[c as usize].as_ptr()))"
            )
            .unwrap();
            writeln!(f, "        }};").unwrap();
        }
    }

    writeln!(f).unwrap();
    writeln!(f, "        let bytes_done = shard_len & !15usize;").unwrap();
    writeln!(f).unwrap();
    writeln!(
        f,
        "        // Main SIMD loop: process 16 bytes per iteration."
    )
    .unwrap();
    writeln!(f, "        let mut offset = 0usize;").unwrap();
    writeln!(f, "        while offset < bytes_done {{").unwrap();
    writeln!(f, "        unsafe {{").unwrap();

    // Load all data shards
    for di in 0..d {
        writeln!(
            f,
            "            let d{di}: uint8x16_t = vld1q_u8(data[{di}][offset..].as_ptr());"
        )
        .unwrap();
    }

    writeln!(f).unwrap();

    // Compute each parity shard
    for pi in 0..p {
        writeln!(f, "            // Compute parity shard {pi}.").unwrap();
        writeln!(f, "            let low = vandq_u8(d0, nibble_mask);").unwrap();
        writeln!(f, "            let high = vshrq_n_u8::<4>(d0);").unwrap();
        writeln!(f, "            let mut acc_{pi}: uint8x16_t = veorq_u8(").unwrap();
        writeln!(f, "                vqtbl1q_u8(coef_low_{pi}_0, low),").unwrap();
        writeln!(f, "                vqtbl1q_u8(coef_high_{pi}_0, high),").unwrap();
        writeln!(f, "            );").unwrap();

        for di in 1..d {
            writeln!(f, "            let low = vandq_u8(d{di}, nibble_mask);").unwrap();
            writeln!(f, "            let high = vshrq_n_u8::<4>(d{di});").unwrap();
            writeln!(f, "            acc_{pi} = veorq_u8(acc_{pi}, veorq_u8(").unwrap();
            writeln!(f, "                vqtbl1q_u8(coef_low_{pi}_{di}, low),").unwrap();
            writeln!(f, "                vqtbl1q_u8(coef_high_{pi}_{di}, high),").unwrap();
            writeln!(f, "            ));").unwrap();
        }

        writeln!(
            f,
            "            vst1q_u8(parity[{pi}][offset..].as_mut_ptr(), acc_{pi});"
        )
        .unwrap();
    }

    writeln!(f, "        }}").unwrap(); // close unsafe block
    writeln!(f, "            offset += 16;").unwrap();
    writeln!(f, "        }}").unwrap();

    // Scalar tail
    writeln!(f).unwrap();
    writeln!(f, "        // Scalar tail for remaining bytes.").unwrap();
    writeln!(f, "        for i in bytes_done..shard_len {{").unwrap();
    for pi in 0..p {
        writeln!(f, "            let mut acc: u8 = 0;").unwrap();
        for di in 0..d {
            writeln!(f, "            acc ^= super::super::super::MUL_TABLE[parity_rows[{pi}][{di}] as usize][data[{di}][i] as usize];").unwrap();
        }
        writeln!(f, "            parity[{pi}][i] = acc;").unwrap();
    }
    writeln!(f, "        }}").unwrap();

    writeln!(f, "    }}").unwrap();
    writeln!(f).unwrap();
}

fn main() {
    println!("cargo:rerun-if-env-changed=RUST_REED_SOLOMON_ERASURE_ARCH");
    println!("cargo:rerun-if-changed=simd_c/reedsolomon.c");
    println!("cargo:rerun-if-changed=simd_c/reedsolomon.h");
    println!("cargo:rustc-check-cfg=cfg(rse_simd_c_build_baseline)");
    println!("cargo:rustc-check-cfg=cfg(rse_simd_c_build_unknown)");
    compile_simd_c();
    write_tables();
    generate_encode_codegen();
}