coreutils_rs/cut/

core.rs

use memchr::memchr_iter;
use rayon::prelude::*;
use std::io::{self, BufRead, Write};

/// Minimum file size for parallel processing (1MB).
/// Rayon overhead is ~5-10μs per task; at 1MB per chunk,
/// each chunk takes ~100μs+ to process, so overhead is < 10%.
const PARALLEL_THRESHOLD: usize = 1024 * 1024;

/// Configuration for cut operations.
pub struct CutConfig<'a> {
    pub mode: CutMode,
    pub ranges: &'a [Range],
    pub complement: bool,
    pub delim: u8,
    pub output_delim: &'a [u8],
    pub suppress_no_delim: bool,
    pub line_delim: u8,
}

/// A range specification like 1, 3-5, -3, 4-
#[derive(Debug, Clone)]
pub struct Range {
    pub start: usize, // 1-based, 0 means "from beginning"
    pub end: usize,   // 1-based, usize::MAX means "to end"
}

/// Parse a LIST specification like "1,3-5,7-" into ranges.
/// Each range is 1-based. Returns sorted, merged ranges.
pub fn parse_ranges(spec: &str) -> Result<Vec<Range>, String> {
    let mut ranges = Vec::new();

    for part in spec.split(',') {
        let part = part.trim();
        if part.is_empty() {
            continue;
        }

        if let Some(idx) = part.find('-') {
            let left = &part[..idx];
            let right = &part[idx + 1..];

            let start = if left.is_empty() {
                1
            } else {
                left.parse::<usize>()
                    .map_err(|_| format!("invalid range: '{}'", part))?
            };

            let end = if right.is_empty() {
                usize::MAX
            } else {
                right
                    .parse::<usize>()
                    .map_err(|_| format!("invalid range: '{}'", part))?
            };

            if start == 0 {
                return Err("fields and positions are numbered from 1".to_string());
            }
            if start > end {
                return Err(format!("invalid decreasing range: '{}'", part));
            }

            ranges.push(Range { start, end });
        } else {
            let n = part
                .parse::<usize>()
                .map_err(|_| format!("invalid field: '{}'", part))?;
            if n == 0 {
                return Err("fields and positions are numbered from 1".to_string());
            }
            ranges.push(Range { start: n, end: n });
        }
    }

    if ranges.is_empty() {
        return Err("you must specify a list of bytes, characters, or fields".to_string());
    }

    // Sort and merge overlapping ranges
    ranges.sort_by_key(|r| (r.start, r.end));
    let mut merged = vec![ranges[0].clone()];
    for r in &ranges[1..] {
        let last = merged.last_mut().unwrap();
        if r.start <= last.end.saturating_add(1) {
            last.end = last.end.max(r.end);
        } else {
            merged.push(r.clone());
        }
    }

    Ok(merged)
}

/// Check if a 1-based position is in any range.
/// Ranges must be sorted. Uses early exit since ranges are sorted.
#[inline(always)]
fn in_ranges(ranges: &[Range], pos: usize) -> bool {
    for r in ranges {
        if pos < r.start {
            return false; // ranges are sorted, no point checking further
        }
        if pos <= r.end {
            return true;
        }
    }
    false
}

/// Pre-compute a 64-bit mask for field selection.
/// Bit i-1 is set if field i should be output.
#[inline]
fn compute_field_mask(ranges: &[Range], complement: bool) -> u64 {
    let mut mask: u64 = 0;
    for i in 1..=64u32 {
        let in_range = in_ranges(ranges, i as usize);
        if in_range != complement {
            mask |= 1u64 << (i - 1);
        }
    }
    mask
}

/// Check if a field should be selected, using bitset for first 64 fields.
#[inline(always)]
fn is_selected(field_num: usize, mask: u64, ranges: &[Range], complement: bool) -> bool {
    if field_num <= 64 {
        (mask >> (field_num - 1)) & 1 == 1
    } else {
        in_ranges(ranges, field_num) != complement
    }
}

// ── Chunk splitting for parallel processing ──────────────────────────────

/// Split data into chunks aligned to line boundaries for parallel processing.
/// Returns slices that each end on a line_delim boundary (except possibly the last).
fn split_into_chunks<'a>(data: &'a [u8], line_delim: u8) -> Vec<&'a [u8]> {
    let num_threads = rayon::current_num_threads().max(1);
    if data.len() < PARALLEL_THRESHOLD || num_threads <= 1 {
        return vec![data];
    }

    let chunk_size = data.len() / num_threads;
    let mut chunks = Vec::with_capacity(num_threads);
    let mut pos = 0;

    for _ in 0..num_threads - 1 {
        let target = pos + chunk_size;
        if target >= data.len() {
            break;
        }
        // Align to next line boundary
        let boundary = memchr::memchr(line_delim, &data[target..])
            .map(|p| target + p + 1)
            .unwrap_or(data.len());
        if boundary > pos {
            chunks.push(&data[pos..boundary]);
        }
        pos = boundary;
    }

    // Last chunk gets the remainder
    if pos < data.len() {
        chunks.push(&data[pos..]);
    }

    chunks
}

// ── Fast path: field extraction with batched output ──────────────────────

/// Optimized field extraction with early exit and batched output.
/// Uses SIMD newline scanning + inline byte scan per line.
fn process_fields_fast(data: &[u8], cfg: &CutConfig, out: &mut impl Write) -> io::Result<()> {
    let delim = cfg.delim;
    let line_delim = cfg.line_delim;
    let ranges = cfg.ranges;
    let complement = cfg.complement;
    let output_delim = cfg.output_delim;
    let suppress = cfg.suppress_no_delim;

    // Ultra-fast path: single field extraction (e.g., cut -f5)
    if !complement && ranges.len() == 1 && ranges[0].start == ranges[0].end {
        return process_single_field(data, delim, line_delim, ranges[0].start, suppress, out);
    }

    // Pre-compute for general field extraction
    let max_field = if complement {
        usize::MAX
    } else {
        ranges.last().map(|r| r.end).unwrap_or(0)
    };
    let field_mask = compute_field_mask(ranges, complement);

    if data.len() >= PARALLEL_THRESHOLD {
        // Parallel path
        let chunks = split_into_chunks(data, line_delim);
        let results: Vec<Vec<u8>> = chunks
            .par_iter()
            .map(|chunk| {
                let mut buf = Vec::with_capacity(chunk.len() / 2);
                process_fields_chunk(
                    chunk,
                    delim,
                    ranges,
                    output_delim,
                    suppress,
                    max_field,
                    field_mask,
                    line_delim,
                    complement,
                    &mut buf,
                );
                buf
            })
            .collect();
        for result in &results {
            if !result.is_empty() {
                out.write_all(result)?;
            }
        }
    } else {
        // Sequential path
        let mut buf = Vec::with_capacity(data.len() / 2);
        process_fields_chunk(
            data,
            delim,
            ranges,
            output_delim,
            suppress,
            max_field,
            field_mask,
            line_delim,
            complement,
            &mut buf,
        );
        if !buf.is_empty() {
            out.write_all(&buf)?;
        }
    }
    Ok(())
}

/// Process a chunk of data for general field extraction.
fn process_fields_chunk(
    data: &[u8],
    delim: u8,
    ranges: &[Range],
    output_delim: &[u8],
    suppress: bool,
    max_field: usize,
    field_mask: u64,
    line_delim: u8,
    complement: bool,
    buf: &mut Vec<u8>,
) {
    let mut start = 0;
    for end_pos in memchr_iter(line_delim, data) {
        let line = &data[start..end_pos];
        extract_fields_to_buf(
            line,
            delim,
            ranges,
            output_delim,
            suppress,
            max_field,
            field_mask,
            line_delim,
            buf,
            complement,
        );
        start = end_pos + 1;
    }
    if start < data.len() {
        extract_fields_to_buf(
            &data[start..],
            delim,
            ranges,
            output_delim,
            suppress,
            max_field,
            field_mask,
            line_delim,
            buf,
            complement,
        );
    }
}

// ── Ultra-fast single field extraction ───────────────────────────────────

/// Specialized path for extracting exactly one field (e.g., `cut -f5`).
/// Uses SIMD memchr for newline scanning + minimal inline byte scan per line.
/// For large files, splits work across multiple threads with rayon.
fn process_single_field(
    data: &[u8],
    delim: u8,
    line_delim: u8,
    target: usize,
    suppress: bool,
    out: &mut impl Write,
) -> io::Result<()> {
    let target_idx = target - 1;

    if data.len() >= PARALLEL_THRESHOLD {
        // Parallel path: split into chunks aligned to line boundaries
        let chunks = split_into_chunks(data, line_delim);
        let results: Vec<Vec<u8>> = chunks
            .par_iter()
            .map(|chunk| {
                let mut buf = Vec::with_capacity(chunk.len() / 4);
                process_single_field_chunk(
                    chunk, delim, target_idx, line_delim, suppress, &mut buf,
                );
                buf
            })
            .collect();
        for result in &results {
            if !result.is_empty() {
                out.write_all(result)?;
            }
        }
    } else {
        // Sequential path for small data
        let mut buf = Vec::with_capacity(data.len() / 4);
        process_single_field_chunk(data, delim, target_idx, line_delim, suppress, &mut buf);
        if !buf.is_empty() {
            out.write_all(&buf)?;
        }
    }
    Ok(())
}

/// Process a chunk of data for single-field extraction.
fn process_single_field_chunk(
    data: &[u8],
    delim: u8,
    target_idx: usize,
    line_delim: u8,
    suppress: bool,
    buf: &mut Vec<u8>,
) {
    let mut start = 0;
    for end_pos in memchr_iter(line_delim, data) {
        let line = &data[start..end_pos];
        extract_single_field_line(line, delim, target_idx, line_delim, suppress, buf);
        start = end_pos + 1;
    }
    // Handle final line without terminator
    if start < data.len() {
        extract_single_field_line(&data[start..], delim, target_idx, line_delim, suppress, buf);
    }
}

/// Extract a single field from one line using a single SIMD memchr_iter pass.
/// Collects all delimiter positions in one scan, then indexes directly.
#[inline(always)]
fn extract_single_field_line(
    line: &[u8],
    delim: u8,
    target_idx: usize,
    line_delim: u8,
    suppress: bool,
    buf: &mut Vec<u8>,
) {
    if line.is_empty() {
        if !suppress {
            buf.push(line_delim);
        }
        return;
    }

    // Single SIMD pass to find ALL delimiter positions
    // This reduces N SIMD scans to 1 for field N
    let mut delim_positions: [usize; 64] = [0; 64];
    let mut num_delims: usize = 0;

    for pos in memchr_iter(delim, line) {
        if num_delims < 64 {
            delim_positions[num_delims] = pos;
        }
        num_delims += 1;
        // Early exit: we have enough delimiters to extract our target field
        if num_delims > target_idx {
            break;
        }
    }

    // No delimiters found — output whole line or suppress
    if num_delims == 0 {
        if !suppress {
            buf.extend_from_slice(line);
            buf.push(line_delim);
        }
        return;
    }

    // Fast path: target is field 1 (cut -f1)
    if target_idx == 0 {
        buf.extend_from_slice(&line[..delim_positions[0]]);
        buf.push(line_delim);
        return;
    }

    // Not enough fields for target
    if num_delims < target_idx {
        buf.push(line_delim);
        return;
    }

    // Field start is right after the (target_idx-1)th delimiter
    let field_start = delim_positions[target_idx - 1] + 1;

    // Field end is the target_idx-th delimiter (or end of line)
    if num_delims > target_idx && target_idx < 64 {
        buf.extend_from_slice(&line[field_start..delim_positions[target_idx]]);
    } else {
        buf.extend_from_slice(&line[field_start..]);
    }
    buf.push(line_delim);
}

/// Extract fields from a single line into the output buffer.
/// Uses inline byte scanning with early exit for maximum performance.
#[inline(always)]
fn extract_fields_to_buf(
    line: &[u8],
    delim: u8,
    ranges: &[Range],
    output_delim: &[u8],
    suppress: bool,
    max_field: usize,
    field_mask: u64,
    line_delim: u8,
    buf: &mut Vec<u8>,
    complement: bool,
) {
    let len = line.len();

    // Empty line: no delimiter possible
    if len == 0 {
        if !suppress {
            buf.push(line_delim);
        }
        return;
    }

    let mut field_num: usize = 1;
    let mut field_start: usize = 0;
    let mut first_output = true;
    let mut has_delim = false;

    // SIMD-accelerated delimiter scanning with early exit
    for delim_pos in memchr_iter(delim, line) {
        has_delim = true;

        if is_selected(field_num, field_mask, ranges, complement) {
            if !first_output {
                buf.extend_from_slice(output_delim);
            }
            buf.extend_from_slice(&line[field_start..delim_pos]);
            first_output = false;
        }

        field_num += 1;
        field_start = delim_pos + 1;

        // Early exit: past the last needed field
        if field_num > max_field {
            break;
        }
    }

    // Last field (only if we didn't early-exit past it)
    if (field_num <= max_field || complement)
        && has_delim
        && is_selected(field_num, field_mask, ranges, complement)
    {
        if !first_output {
            buf.extend_from_slice(output_delim);
        }
        buf.extend_from_slice(&line[field_start..len]);
        first_output = false;
    }

    // Output line terminator
    if !first_output {
        // Had output — add line delimiter
        buf.push(line_delim);
    } else if !has_delim {
        // No delimiter found — output whole line or suppress
        if !suppress {
            buf.extend_from_slice(line);
            buf.push(line_delim);
        }
    } else {
        // Had delimiter but no selected field — output empty line (GNU compat)
        buf.push(line_delim);
    }
}

// ── Fast path: byte/char extraction with batched output ──────────────────

/// Optimized byte/char extraction with batched output and parallel processing.
fn process_bytes_fast(data: &[u8], cfg: &CutConfig, out: &mut impl Write) -> io::Result<()> {
    let line_delim = cfg.line_delim;
    let ranges = cfg.ranges;
    let complement = cfg.complement;
    let output_delim = cfg.output_delim;

    if data.len() >= PARALLEL_THRESHOLD {
        let chunks = split_into_chunks(data, line_delim);
        let results: Vec<Vec<u8>> = chunks
            .par_iter()
            .map(|chunk| {
                let mut buf = Vec::with_capacity(chunk.len() / 2);
                process_bytes_chunk(
                    chunk,
                    ranges,
                    complement,
                    output_delim,
                    line_delim,
                    &mut buf,
                );
                buf
            })
            .collect();
        for result in &results {
            if !result.is_empty() {
                out.write_all(result)?;
            }
        }
    } else {
        let mut buf = Vec::with_capacity(data.len() / 2);
        process_bytes_chunk(data, ranges, complement, output_delim, line_delim, &mut buf);
        if !buf.is_empty() {
            out.write_all(&buf)?;
        }
    }
    Ok(())
}

/// Process a chunk of data for byte/char extraction.
fn process_bytes_chunk(
    data: &[u8],
    ranges: &[Range],
    complement: bool,
    output_delim: &[u8],
    line_delim: u8,
    buf: &mut Vec<u8>,
) {
    let mut start = 0;
    for end_pos in memchr_iter(line_delim, data) {
        let line = &data[start..end_pos];
        cut_bytes_to_buf(line, ranges, complement, output_delim, buf);
        buf.push(line_delim);
        start = end_pos + 1;
    }
    if start < data.len() {
        cut_bytes_to_buf(&data[start..], ranges, complement, output_delim, buf);
        buf.push(line_delim);
    }
}

/// Extract byte ranges from a line into the output buffer.
/// For the common non-complement case with contiguous ranges, uses bulk copy.
#[inline(always)]
fn cut_bytes_to_buf(
    line: &[u8],
    ranges: &[Range],
    complement: bool,
    output_delim: &[u8],
    buf: &mut Vec<u8>,
) {
    let len = line.len();
    let mut first_range = true;

    if complement {
        let mut pos: usize = 1;
        for r in ranges {
            let rs = r.start;
            let re = r.end.min(len);
            if pos < rs {
                if !first_range && !output_delim.is_empty() {
                    buf.extend_from_slice(output_delim);
                }
                buf.extend_from_slice(&line[pos - 1..rs - 1]);
                first_range = false;
            }
            pos = re + 1;
            if pos > len {
                break;
            }
        }
        if pos <= len {
            if !first_range && !output_delim.is_empty() {
                buf.extend_from_slice(output_delim);
            }
            buf.extend_from_slice(&line[pos - 1..len]);
        }
    } else if output_delim.is_empty() && ranges.len() == 1 {
        // Ultra-fast path: single range, no output delimiter
        let start = ranges[0].start.saturating_sub(1);
        let end = ranges[0].end.min(len);
        if start < len {
            buf.extend_from_slice(&line[start..end]);
        }
    } else {
        for r in ranges {
            let start = r.start.saturating_sub(1);
            let end = r.end.min(len);
            if start >= len {
                break;
            }
            if !first_range && !output_delim.is_empty() {
                buf.extend_from_slice(output_delim);
            }
            buf.extend_from_slice(&line[start..end]);
            first_range = false;
        }
    }
}

// ── Public API ───────────────────────────────────────────────────────────

/// Cut fields from a line using a delimiter. Writes to `out`.
/// Returns true if any output was written, false if suppressed.
/// Used by process_cut_reader (stdin path) and unit tests.
#[inline]
pub fn cut_fields(
    line: &[u8],
    delim: u8,
    ranges: &[Range],
    complement: bool,
    output_delim: &[u8],
    suppress_no_delim: bool,
    out: &mut impl Write,
) -> io::Result<bool> {
    // Check if line contains delimiter at all
    if memchr::memchr(delim, line).is_none() {
        if !suppress_no_delim {
            out.write_all(line)?;
            return Ok(true);
        }
        return Ok(false); // suppressed
    }

    // Walk through fields using memchr, output selected ones
    let mut field_num: usize = 1;
    let mut field_start: usize = 0;
    let mut first_output = true;

    for delim_pos in memchr_iter(delim, line) {
        let selected = in_ranges(ranges, field_num) != complement;
        if selected {
            if !first_output {
                out.write_all(output_delim)?;
            }
            out.write_all(&line[field_start..delim_pos])?;
            first_output = false;
        }
        field_start = delim_pos + 1;
        field_num += 1;
    }

    // Last field (after last delimiter)
    let selected = in_ranges(ranges, field_num) != complement;
    if selected {
        if !first_output {
            out.write_all(output_delim)?;
        }
        out.write_all(&line[field_start..])?;
    }

    Ok(true)
}

/// Cut bytes/chars from a line. Writes selected bytes to `out`.
/// Used by process_cut_reader (stdin path) and unit tests.
#[inline]
pub fn cut_bytes(
    line: &[u8],
    ranges: &[Range],
    complement: bool,
    output_delim: &[u8],
    out: &mut impl Write,
) -> io::Result<bool> {
    let mut first_range = true;

    if complement {
        let len = line.len();
        let mut comp_ranges = Vec::new();
        let mut pos: usize = 1;
        for r in ranges {
            let rs = r.start;
            let re = r.end.min(len);
            if pos < rs {
                comp_ranges.push((pos, rs - 1));
            }
            pos = re + 1;
            if pos > len {
                break;
            }
        }
        if pos <= len {
            comp_ranges.push((pos, len));
        }
        for &(s, e) in &comp_ranges {
            if !first_range && !output_delim.is_empty() {
                out.write_all(output_delim)?;
            }
            out.write_all(&line[s - 1..e])?;
            first_range = false;
        }
    } else {
        for r in ranges {
            let start = r.start.saturating_sub(1);
            let end = r.end.min(line.len());
            if start >= line.len() {
                break;
            }
            if !first_range && !output_delim.is_empty() {
                out.write_all(output_delim)?;
            }
            out.write_all(&line[start..end])?;
            first_range = false;
        }
    }
    Ok(true)
}

/// Process a full data buffer (from mmap or read) with cut operation.
/// Dispatches to optimized fast paths for field and byte modes.
pub fn process_cut_data(data: &[u8], cfg: &CutConfig, out: &mut impl Write) -> io::Result<()> {
    match cfg.mode {
        CutMode::Fields => process_fields_fast(data, cfg, out),
        CutMode::Bytes | CutMode::Characters => process_bytes_fast(data, cfg, out),
    }
}

/// Process input from a reader (for stdin).
pub fn process_cut_reader<R: BufRead>(
    mut reader: R,
    cfg: &CutConfig,
    out: &mut impl Write,
) -> io::Result<()> {
    let mut buf = Vec::new();

    loop {
        buf.clear();
        let n = reader.read_until(cfg.line_delim, &mut buf)?;
        if n == 0 {
            break;
        }

        let has_line_delim = buf.last() == Some(&cfg.line_delim);
        let line = if has_line_delim {
            &buf[..buf.len() - 1]
        } else {
            &buf[..]
        };

        let wrote = process_one_line(line, cfg, out)?;

        // GNU always terminates output lines, even if input had no trailing delimiter
        if wrote {
            out.write_all(&[cfg.line_delim])?;
        }
    }

    Ok(())
}

/// Process one line according to the cut config (used by stdin reader path).
#[inline]
fn process_one_line(line: &[u8], cfg: &CutConfig, out: &mut impl Write) -> io::Result<bool> {
    match cfg.mode {
        CutMode::Fields => cut_fields(
            line,
            cfg.delim,
            cfg.ranges,
            cfg.complement,
            cfg.output_delim,
            cfg.suppress_no_delim,
            out,
        ),
        CutMode::Bytes | CutMode::Characters => {
            cut_bytes(line, cfg.ranges, cfg.complement, cfg.output_delim, out)
        }
    }
}

/// Cut operation mode
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum CutMode {
    Bytes,
    Characters,
    Fields,
}