coreutils_rs/tr/

core.rs

use std::io::{self, Read, Write};

/// Main processing buffer: 4MB — large enough to amortize write() syscall overhead
/// while still fitting in L3 cache.
const BUF_SIZE: usize = 4 * 1024 * 1024;

/// Stream buffer: 1MB — process data immediately after each read().
/// Larger than typical pipe buffer (64KB) to batch multiple reads into one process cycle.
const STREAM_BUF: usize = 1024 * 1024;

/// Build a 256-byte lookup table mapping set1[i] -> set2[i].
#[inline]
fn build_translate_table(set1: &[u8], set2: &[u8]) -> [u8; 256] {
    let mut table: [u8; 256] = std::array::from_fn(|i| i as u8);
    let last = set2.last().copied();
    for (i, &from) in set1.iter().enumerate() {
        table[from as usize] = if i < set2.len() {
            set2[i]
        } else {
            last.unwrap_or(from)
        };
    }
    table
}

/// Build a 256-bit (32-byte) membership set for O(1) byte lookup.
#[inline]
fn build_member_set(chars: &[u8]) -> [u8; 32] {
    let mut set = [0u8; 32];
    for &ch in chars {
        set[ch as usize >> 3] |= 1 << (ch & 7);
    }
    set
}

#[inline(always)]
fn is_member(set: &[u8; 32], ch: u8) -> bool {
    unsafe { (*set.get_unchecked(ch as usize >> 3) & (1 << (ch & 7))) != 0 }
}

/// Translate bytes in-place using a 256-byte lookup table.
/// The table fits in L1 cache (256 bytes). The simple loop auto-vectorizes via LLVM.
#[inline(always)]
fn translate_inplace(data: &mut [u8], table: &[u8; 256]) {
    for b in data.iter_mut() {
        *b = table[*b as usize];
    }
}

// ============================================================================
// Streaming functions (Read + Write)
// ============================================================================

pub fn translate(
    set1: &[u8],
    set2: &[u8],
    reader: &mut impl Read,
    writer: &mut impl Write,
) -> io::Result<()> {
    let table = build_translate_table(set1, set2);
    let mut buf = vec![0u8; BUF_SIZE];
    loop {
        let n = match reader.read(&mut buf) {
            Ok(0) => break,
            Ok(n) => n,
            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
            Err(e) => return Err(e),
        };
        translate_inplace(&mut buf[..n], &table);
        writer.write_all(&buf[..n])?;
    }
    Ok(())
}

pub fn translate_squeeze(
    set1: &[u8],
    set2: &[u8],
    reader: &mut impl Read,
    writer: &mut impl Write,
) -> io::Result<()> {
    let table = build_translate_table(set1, set2);
    let squeeze_set = build_member_set(set2);

    let mut buf = vec![0u8; STREAM_BUF];
    let mut last_squeezed: u16 = 256;

    loop {
        let n = match reader.read(&mut buf) {
            Ok(0) => break,
            Ok(n) => n,
            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
            Err(e) => return Err(e),
        };
        // Phase 1: translate in-place
        translate_inplace(&mut buf[..n], &table);
        // Phase 2: squeeze in-place compaction (wp <= i always, safe)
        let mut wp = 0;
        unsafe {
            let ptr = buf.as_mut_ptr();
            for i in 0..n {
                let b = *ptr.add(i);
                if is_member(&squeeze_set, b) {
                    if last_squeezed == b as u16 {
                        continue;
                    }
                    last_squeezed = b as u16;
                } else {
                    last_squeezed = 256;
                }
                *ptr.add(wp) = b;
                wp += 1;
            }
        }
        writer.write_all(&buf[..wp])?;
    }
    Ok(())
}

pub fn delete(
    delete_chars: &[u8],
    reader: &mut impl Read,
    writer: &mut impl Write,
) -> io::Result<()> {
    // Fast path: single character delete using SIMD memchr
    if delete_chars.len() == 1 {
        return delete_single_streaming(delete_chars[0], reader, writer);
    }

    // Fast paths: 2-3 char delete using SIMD memchr2/memchr3
    if delete_chars.len() <= 3 {
        return delete_multi_streaming(delete_chars, reader, writer);
    }

    let member = build_member_set(delete_chars);
    // Single buffer with in-place compaction — eliminates outbuf allocation + memcpy
    let mut buf = vec![0u8; STREAM_BUF];

    loop {
        let n = match reader.read(&mut buf) {
            Ok(0) => break,
            Ok(n) => n,
            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
            Err(e) => return Err(e),
        };
        let mut wp = 0;
        unsafe {
            let ptr = buf.as_mut_ptr();
            let mut i = 0;
            // 8-byte unrolled in-place compaction
            while i + 8 <= n {
                let b0 = *ptr.add(i);
                let b1 = *ptr.add(i + 1);
                let b2 = *ptr.add(i + 2);
                let b3 = *ptr.add(i + 3);
                let b4 = *ptr.add(i + 4);
                let b5 = *ptr.add(i + 5);
                let b6 = *ptr.add(i + 6);
                let b7 = *ptr.add(i + 7);

                if !is_member(&member, b0) {
                    *ptr.add(wp) = b0;
                    wp += 1;
                }
                if !is_member(&member, b1) {
                    *ptr.add(wp) = b1;
                    wp += 1;
                }
                if !is_member(&member, b2) {
                    *ptr.add(wp) = b2;
                    wp += 1;
                }
                if !is_member(&member, b3) {
                    *ptr.add(wp) = b3;
                    wp += 1;
                }
                if !is_member(&member, b4) {
                    *ptr.add(wp) = b4;
                    wp += 1;
                }
                if !is_member(&member, b5) {
                    *ptr.add(wp) = b5;
                    wp += 1;
                }
                if !is_member(&member, b6) {
                    *ptr.add(wp) = b6;
                    wp += 1;
                }
                if !is_member(&member, b7) {
                    *ptr.add(wp) = b7;
                    wp += 1;
                }
                i += 8;
            }
            while i < n {
                let b = *ptr.add(i);
                if !is_member(&member, b) {
                    *ptr.add(wp) = b;
                    wp += 1;
                }
                i += 1;
            }
        }
        writer.write_all(&buf[..wp])?;
    }
    Ok(())
}

/// Single-character delete from a reader — in-place compaction with SIMD memchr.
fn delete_single_streaming(
    ch: u8,
    reader: &mut impl Read,
    writer: &mut impl Write,
) -> io::Result<()> {
    let mut buf = vec![0u8; STREAM_BUF];
    loop {
        let n = match reader.read(&mut buf) {
            Ok(0) => break,
            Ok(n) => n,
            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
            Err(e) => return Err(e),
        };
        let mut wp = 0;
        let mut i = 0;
        while i < n {
            match memchr::memchr(ch, &buf[i..n]) {
                Some(offset) => {
                    if offset > 0 {
                        if wp != i {
                            unsafe {
                                std::ptr::copy(
                                    buf.as_ptr().add(i),
                                    buf.as_mut_ptr().add(wp),
                                    offset,
                                );
                            }
                        }
                        wp += offset;
                    }
                    i += offset + 1; // skip the deleted char
                }
                None => {
                    let run_len = n - i;
                    if run_len > 0 {
                        if wp != i {
                            unsafe {
                                std::ptr::copy(
                                    buf.as_ptr().add(i),
                                    buf.as_mut_ptr().add(wp),
                                    run_len,
                                );
                            }
                        }
                        wp += run_len;
                    }
                    break;
                }
            }
        }
        writer.write_all(&buf[..wp])?;
    }
    Ok(())
}

/// Multi-character delete (2-3 chars) — in-place compaction with SIMD memchr2/memchr3.
fn delete_multi_streaming(
    chars: &[u8],
    reader: &mut impl Read,
    writer: &mut impl Write,
) -> io::Result<()> {
    let mut buf = vec![0u8; STREAM_BUF];
    loop {
        let n = match reader.read(&mut buf) {
            Ok(0) => break,
            Ok(n) => n,
            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
            Err(e) => return Err(e),
        };
        let mut wp = 0;
        let mut i = 0;
        while i < n {
            let found = if chars.len() == 2 {
                memchr::memchr2(chars[0], chars[1], &buf[i..n])
            } else {
                memchr::memchr3(chars[0], chars[1], chars[2], &buf[i..n])
            };
            match found {
                Some(offset) => {
                    if offset > 0 {
                        if wp != i {
                            unsafe {
                                std::ptr::copy(
                                    buf.as_ptr().add(i),
                                    buf.as_mut_ptr().add(wp),
                                    offset,
                                );
                            }
                        }
                        wp += offset;
                    }
                    i += offset + 1;
                }
                None => {
                    let run_len = n - i;
                    if run_len > 0 {
                        if wp != i {
                            unsafe {
                                std::ptr::copy(
                                    buf.as_ptr().add(i),
                                    buf.as_mut_ptr().add(wp),
                                    run_len,
                                );
                            }
                        }
                        wp += run_len;
                    }
                    break;
                }
            }
        }
        writer.write_all(&buf[..wp])?;
    }
    Ok(())
}

pub fn delete_squeeze(
    delete_chars: &[u8],
    squeeze_chars: &[u8],
    reader: &mut impl Read,
    writer: &mut impl Write,
) -> io::Result<()> {
    let delete_set = build_member_set(delete_chars);
    let squeeze_set = build_member_set(squeeze_chars);
    // Single buffer with in-place compaction
    let mut buf = vec![0u8; STREAM_BUF];
    let mut last_squeezed: u16 = 256;

    loop {
        let n = match reader.read(&mut buf) {
            Ok(0) => break,
            Ok(n) => n,
            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
            Err(e) => return Err(e),
        };
        let mut wp = 0;
        unsafe {
            let ptr = buf.as_mut_ptr();
            for i in 0..n {
                let b = *ptr.add(i);
                if is_member(&delete_set, b) {
                    continue;
                }
                if is_member(&squeeze_set, b) {
                    if last_squeezed == b as u16 {
                        continue;
                    }
                    last_squeezed = b as u16;
                } else {
                    last_squeezed = 256;
                }
                *ptr.add(wp) = b;
                wp += 1;
            }
        }
        writer.write_all(&buf[..wp])?;
    }
    Ok(())
}

pub fn squeeze(
    squeeze_chars: &[u8],
    reader: &mut impl Read,
    writer: &mut impl Write,
) -> io::Result<()> {
    // Fast path: single squeeze char — bulk copy non-match runs
    if squeeze_chars.len() == 1 {
        return squeeze_single_stream(squeeze_chars[0], reader, writer);
    }

    let member = build_member_set(squeeze_chars);
    // Single buffer with in-place compaction — eliminates outbuf allocation + memcpy
    let mut buf = vec![0u8; STREAM_BUF];
    let mut last_squeezed: u16 = 256;

    loop {
        let n = match reader.read(&mut buf) {
            Ok(0) => break,
            Ok(n) => n,
            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
            Err(e) => return Err(e),
        };
        let mut wp = 0;
        unsafe {
            let ptr = buf.as_mut_ptr();
            for i in 0..n {
                let b = *ptr.add(i);
                if is_member(&member, b) {
                    if last_squeezed == b as u16 {
                        continue;
                    }
                    last_squeezed = b as u16;
                } else {
                    last_squeezed = 256;
                }
                *ptr.add(wp) = b;
                wp += 1;
            }
        }
        writer.write_all(&buf[..wp])?;
    }
    Ok(())
}

/// Squeeze a single character from a stream — in-place compaction with SIMD memchr.
fn squeeze_single_stream(
    ch: u8,
    reader: &mut impl Read,
    writer: &mut impl Write,
) -> io::Result<()> {
    let mut buf = vec![0u8; STREAM_BUF];
    let mut was_squeeze_char = false;

    loop {
        let n = match reader.read(&mut buf) {
            Ok(0) => break,
            Ok(n) => n,
            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
            Err(e) => return Err(e),
        };

        let mut wp = 0;
        let mut i = 0;

        while i < n {
            // Cross-chunk continuation: skip squeeze chars from previous chunk
            if was_squeeze_char && buf[i] == ch {
                i += 1;
                while i < n && buf[i] == ch {
                    i += 1;
                }
                if i >= n {
                    break;
                }
            }

            // Find next occurrence of squeeze char using SIMD memchr
            match memchr::memchr(ch, &buf[i..n]) {
                Some(offset) => {
                    let run_len = offset;
                    if run_len > 0 {
                        if wp != i {
                            unsafe {
                                std::ptr::copy(
                                    buf.as_ptr().add(i),
                                    buf.as_mut_ptr().add(wp),
                                    run_len,
                                );
                            }
                        }
                        wp += run_len;
                    }
                    i += run_len;

                    // Emit one squeeze char, skip consecutive duplicates
                    unsafe {
                        *buf.as_mut_ptr().add(wp) = ch;
                    }
                    wp += 1;
                    was_squeeze_char = true;
                    i += 1;
                    while i < n && buf[i] == ch {
                        i += 1;
                    }
                }
                None => {
                    let run_len = n - i;
                    if run_len > 0 {
                        if wp != i {
                            unsafe {
                                std::ptr::copy(
                                    buf.as_ptr().add(i),
                                    buf.as_mut_ptr().add(wp),
                                    run_len,
                                );
                            }
                        }
                        wp += run_len;
                    }
                    was_squeeze_char = false;
                    break;
                }
            }
        }

        writer.write_all(&buf[..wp])?;
    }
    Ok(())
}

// ============================================================================
// Mmap-based functions (zero-copy input from byte slice)
// ============================================================================

/// Translate bytes from an mmap'd byte slice.
/// Simple chunked approach: translate into a 4MB buffer, write each chunk.
pub fn translate_mmap(
    set1: &[u8],
    set2: &[u8],
    data: &[u8],
    writer: &mut impl Write,
) -> io::Result<()> {
    let table = build_translate_table(set1, set2);
    let buf_size = data.len().min(BUF_SIZE);
    let mut buf = vec![0u8; buf_size];
    for chunk in data.chunks(buf_size) {
        let out = &mut buf[..chunk.len()];
        for (o, &b) in out.iter_mut().zip(chunk) {
            *o = table[b as usize];
        }
        writer.write_all(out)?;
    }
    Ok(())
}

/// Translate + squeeze from mmap'd byte slice.
pub fn translate_squeeze_mmap(
    set1: &[u8],
    set2: &[u8],
    data: &[u8],
    writer: &mut impl Write,
) -> io::Result<()> {
    let table = build_translate_table(set1, set2);
    let squeeze_set = build_member_set(set2);
    let buf_size = data.len().min(BUF_SIZE);
    let mut buf = vec![0u8; buf_size];
    let mut last_squeezed: u16 = 256;

    for chunk in data.chunks(buf_size) {
        // Translate chunk into buf
        let out = &mut buf[..chunk.len()];
        for (o, &b) in out.iter_mut().zip(chunk) {
            *o = table[b as usize];
        }
        // Squeeze in-place compaction
        let mut wp = 0;
        unsafe {
            let ptr = buf.as_mut_ptr();
            for i in 0..chunk.len() {
                let b = *ptr.add(i);
                if is_member(&squeeze_set, b) {
                    if last_squeezed == b as u16 {
                        continue;
                    }
                    last_squeezed = b as u16;
                } else {
                    last_squeezed = 256;
                }
                *ptr.add(wp) = b;
                wp += 1;
            }
        }
        writer.write_all(&buf[..wp])?;
    }
    Ok(())
}

/// Delete from mmap'd byte slice.
/// Uses SIMD memchr for single/multi char fast paths.
pub fn delete_mmap(delete_chars: &[u8], data: &[u8], writer: &mut impl Write) -> io::Result<()> {
    // Fast path: single character delete uses SIMD memchr
    if delete_chars.len() == 1 {
        return delete_single_char_mmap(delete_chars[0], data, writer);
    }

    // Fast path: 2-3 char delete uses SIMD memchr2/memchr3
    if delete_chars.len() <= 3 {
        return delete_multi_memchr_mmap(delete_chars, data, writer);
    }

    let member = build_member_set(delete_chars);
    let buf_size = data.len().min(BUF_SIZE);
    let mut outbuf = vec![0u8; buf_size];

    for chunk in data.chunks(buf_size) {
        let mut out_pos = 0;
        let len = chunk.len();
        let mut i = 0;

        while i + 8 <= len {
            unsafe {
                let b0 = *chunk.get_unchecked(i);
                let b1 = *chunk.get_unchecked(i + 1);
                let b2 = *chunk.get_unchecked(i + 2);
                let b3 = *chunk.get_unchecked(i + 3);
                let b4 = *chunk.get_unchecked(i + 4);
                let b5 = *chunk.get_unchecked(i + 5);
                let b6 = *chunk.get_unchecked(i + 6);
                let b7 = *chunk.get_unchecked(i + 7);

                *outbuf.get_unchecked_mut(out_pos) = b0;
                out_pos += !is_member(&member, b0) as usize;
                *outbuf.get_unchecked_mut(out_pos) = b1;
                out_pos += !is_member(&member, b1) as usize;
                *outbuf.get_unchecked_mut(out_pos) = b2;
                out_pos += !is_member(&member, b2) as usize;
                *outbuf.get_unchecked_mut(out_pos) = b3;
                out_pos += !is_member(&member, b3) as usize;
                *outbuf.get_unchecked_mut(out_pos) = b4;
                out_pos += !is_member(&member, b4) as usize;
                *outbuf.get_unchecked_mut(out_pos) = b5;
                out_pos += !is_member(&member, b5) as usize;
                *outbuf.get_unchecked_mut(out_pos) = b6;
                out_pos += !is_member(&member, b6) as usize;
                *outbuf.get_unchecked_mut(out_pos) = b7;
                out_pos += !is_member(&member, b7) as usize;
            }
            i += 8;
        }

        while i < len {
            unsafe {
                let b = *chunk.get_unchecked(i);
                *outbuf.get_unchecked_mut(out_pos) = b;
                out_pos += !is_member(&member, b) as usize;
            }
            i += 1;
        }

        writer.write_all(&outbuf[..out_pos])?;
    }
    Ok(())
}

/// Single-character delete from mmap using SIMD memchr + bulk copy between matches.
fn delete_single_char_mmap(ch: u8, data: &[u8], writer: &mut impl Write) -> io::Result<()> {
    let buf_size = data.len().min(BUF_SIZE);
    let mut outbuf = vec![0u8; buf_size];

    for chunk in data.chunks(buf_size) {
        let mut wp = 0;
        let mut last = 0;
        for pos in memchr::memchr_iter(ch, chunk) {
            if pos > last {
                let run = pos - last;
                outbuf[wp..wp + run].copy_from_slice(&chunk[last..pos]);
                wp += run;
            }
            last = pos + 1;
        }
        if last < chunk.len() {
            let run = chunk.len() - last;
            outbuf[wp..wp + run].copy_from_slice(&chunk[last..]);
            wp += run;
        }
        writer.write_all(&outbuf[..wp])?;
    }
    Ok(())
}

/// Multi-character delete (2-3 chars) using SIMD memchr2/memchr3 + bulk copy.
fn delete_multi_memchr_mmap(chars: &[u8], data: &[u8], writer: &mut impl Write) -> io::Result<()> {
    let c0 = chars[0];
    let c1 = if chars.len() >= 2 { chars[1] } else { 0 };
    let c2 = if chars.len() >= 3 { chars[2] } else { 0 };
    let is_three = chars.len() >= 3;

    let buf_size = data.len().min(BUF_SIZE);
    let mut outbuf = vec![0u8; buf_size];

    for chunk in data.chunks(buf_size) {
        let mut wp = 0;
        let mut last = 0;

        let iter_fn = |chunk: &[u8]| -> Vec<usize> {
            if is_three {
                memchr::memchr3_iter(c0, c1, c2, chunk).collect()
            } else {
                memchr::memchr2_iter(c0, c1, chunk).collect()
            }
        };

        for pos in iter_fn(chunk) {
            if pos > last {
                let run = pos - last;
                outbuf[wp..wp + run].copy_from_slice(&chunk[last..pos]);
                wp += run;
            }
            last = pos + 1;
        }

        if last < chunk.len() {
            let run = chunk.len() - last;
            outbuf[wp..wp + run].copy_from_slice(&chunk[last..]);
            wp += run;
        }
        writer.write_all(&outbuf[..wp])?;
    }
    Ok(())
}

/// Delete + squeeze from mmap'd byte slice.
pub fn delete_squeeze_mmap(
    delete_chars: &[u8],
    squeeze_chars: &[u8],
    data: &[u8],
    writer: &mut impl Write,
) -> io::Result<()> {
    let delete_set = build_member_set(delete_chars);
    let squeeze_set = build_member_set(squeeze_chars);
    let buf_size = data.len().min(BUF_SIZE);
    let mut outbuf = vec![0u8; buf_size];
    let mut last_squeezed: u16 = 256;

    for chunk in data.chunks(buf_size) {
        let mut out_pos = 0;
        for &b in chunk {
            if is_member(&delete_set, b) {
                continue;
            }
            if is_member(&squeeze_set, b) {
                if last_squeezed == b as u16 {
                    continue;
                }
                last_squeezed = b as u16;
            } else {
                last_squeezed = 256;
            }
            unsafe {
                *outbuf.get_unchecked_mut(out_pos) = b;
            }
            out_pos += 1;
        }
        writer.write_all(&outbuf[..out_pos])?;
    }
    Ok(())
}

/// Squeeze from mmap'd byte slice.
pub fn squeeze_mmap(squeeze_chars: &[u8], data: &[u8], writer: &mut impl Write) -> io::Result<()> {
    // Fast path: single squeeze character — use SIMD memchr to find runs
    if squeeze_chars.len() == 1 {
        return squeeze_single_mmap(squeeze_chars[0], data, writer);
    }

    // Fast path: 2-3 squeeze chars — use memchr2/memchr3 for SIMD scanning
    if squeeze_chars.len() == 2 {
        return squeeze_multi_mmap::<2>(squeeze_chars, data, writer);
    }
    if squeeze_chars.len() == 3 {
        return squeeze_multi_mmap::<3>(squeeze_chars, data, writer);
    }

    // General path: chunked output buffer with member check
    let member = build_member_set(squeeze_chars);
    let buf_size = data.len().min(BUF_SIZE);
    let mut outbuf = vec![0u8; buf_size];
    let mut last_squeezed: u16 = 256;

    for chunk in data.chunks(buf_size) {
        let len = chunk.len();
        let mut wp = 0;
        let mut i = 0;

        unsafe {
            let inp = chunk.as_ptr();
            let outp = outbuf.as_mut_ptr();

            while i < len {
                let b = *inp.add(i);
                if is_member(&member, b) {
                    if last_squeezed != b as u16 {
                        *outp.add(wp) = b;
                        wp += 1;
                        last_squeezed = b as u16;
                    }
                    i += 1;
                    // Skip consecutive duplicates
                    while i < len && *inp.add(i) == b {
                        i += 1;
                    }
                } else {
                    last_squeezed = 256;
                    *outp.add(wp) = b;
                    wp += 1;
                    i += 1;
                }
            }
        }
        writer.write_all(&outbuf[..wp])?;
    }
    Ok(())
}

/// Squeeze with 2-3 char sets using SIMD memchr2/memchr3 for fast scanning.
fn squeeze_multi_mmap<const N: usize>(
    chars: &[u8],
    data: &[u8],
    writer: &mut impl Write,
) -> io::Result<()> {
    let buf_size = data.len().min(BUF_SIZE);
    let mut outbuf = vec![0u8; buf_size];
    let mut wp = 0;
    let mut last_squeezed: u16 = 256;
    let mut cursor = 0;

    macro_rules! find_next {
        ($data:expr) => {
            if N == 2 {
                memchr::memchr2(chars[0], chars[1], $data)
            } else {
                memchr::memchr3(chars[0], chars[1], chars[2], $data)
            }
        };
    }

    macro_rules! flush_and_copy {
        ($src:expr, $len:expr) => {
            if wp + $len > buf_size {
                writer.write_all(&outbuf[..wp])?;
                wp = 0;
            }
            if $len > buf_size {
                writer.write_all($src)?;
            } else {
                outbuf[wp..wp + $len].copy_from_slice($src);
                wp += $len;
            }
        };
    }

    while cursor < data.len() {
        match find_next!(&data[cursor..]) {
            Some(offset) => {
                let pos = cursor + offset;
                let b = data[pos];
                // Copy non-member span to output buffer
                if pos > cursor {
                    let span = pos - cursor;
                    flush_and_copy!(&data[cursor..pos], span);
                    last_squeezed = 256;
                }
                if last_squeezed != b as u16 {
                    if wp >= buf_size {
                        writer.write_all(&outbuf[..wp])?;
                        wp = 0;
                    }
                    outbuf[wp] = b;
                    wp += 1;
                    last_squeezed = b as u16;
                }
                // Skip consecutive duplicates of same byte
                let mut skip = pos + 1;
                while skip < data.len() && data[skip] == b {
                    skip += 1;
                }
                cursor = skip;
            }
            None => {
                let remaining = data.len() - cursor;
                flush_and_copy!(&data[cursor..], remaining);
                break;
            }
        }
    }
    if wp > 0 {
        writer.write_all(&outbuf[..wp])?;
    }
    Ok(())
}

/// Squeeze a single repeated character from mmap'd data.
/// Uses SIMD memchr for fast scanning + buffered output.
fn squeeze_single_mmap(ch: u8, data: &[u8], writer: &mut impl Write) -> io::Result<()> {
    if data.is_empty() {
        return Ok(());
    }

    // Fast path: no consecutive duplicates — zero-copy output
    if memchr::memmem::find(data, &[ch, ch]).is_none() {
        return writer.write_all(data);
    }

    let buf_size = data.len().min(BUF_SIZE);
    let mut outbuf = vec![0u8; buf_size];
    let len = data.len();
    let mut wp = 0;
    let mut cursor = 0;

    while cursor < len {
        match memchr::memchr(ch, &data[cursor..]) {
            Some(offset) => {
                let pos = cursor + offset;
                let gap = pos - cursor;
                if gap > 0 {
                    if wp + gap > buf_size {
                        writer.write_all(&outbuf[..wp])?;
                        wp = 0;
                    }
                    if gap > buf_size {
                        writer.write_all(&data[cursor..pos])?;
                    } else {
                        outbuf[wp..wp + gap].copy_from_slice(&data[cursor..pos]);
                        wp += gap;
                    }
                }
                if wp >= buf_size {
                    writer.write_all(&outbuf[..wp])?;
                    wp = 0;
                }
                outbuf[wp] = ch;
                wp += 1;
                cursor = pos + 1;
                while cursor < len && data[cursor] == ch {
                    cursor += 1;
                }
            }
            None => {
                let remaining = len - cursor;
                if remaining > 0 {
                    if wp + remaining > buf_size {
                        writer.write_all(&outbuf[..wp])?;
                        wp = 0;
                    }
                    if remaining > buf_size {
                        writer.write_all(&data[cursor..])?;
                    } else {
                        outbuf[wp..wp + remaining].copy_from_slice(&data[cursor..]);
                        wp += remaining;
                    }
                }
                break;
            }
        }
    }

    if wp > 0 {
        writer.write_all(&outbuf[..wp])?;
    }
    Ok(())
}