Merge pull request #637 from AdaWorldAPI/claude/onebrc-lane-s-swar

onebrc-probe: lane S — SWAR delimiter scan + branchless temp parse (+23% v3, +31% native)

Author: AdaWorldAPI

crates/onebrc-probe/src/lane_s.rs

@@ -0,0 +1,163 @@
+//! Lane S — the SWAR lane: the actual 1BRC-frontier compute levers on top of
+//! the flat open-addressed table (lane F's group-by, which was already right).
+//!
+//! What the real 1BRC winners do that lanes A/C/F/R do NOT (see the answer in
+//! the session log): find delimiters with SWAR (8 bytes at a time in a `u64`)
+//! instead of a byte-by-byte `while data[i] != b';'` loop, and parse the
+//! temperature branchlessly. Those are the two measurable levers here.
+//!
+//! - **(b) SWAR delimiter find** — the classic `haszero` bit trick:
+//!   `x = word ^ needle_bcast; (x - 0x0101…) & !x & 0x8080…` sets the high bit
+//!   of each byte where `word == needle`. `trailing_zeros() >> 3` gives the
+//!   first match position. Replaces the scalar name/temp scans.
+//! - **(b) branchless temp parse** — the field is `-?\d?\d.\d`; parse to fixed
+//!   -point tenths with no data-dependent branches beyond the sign/width.
+//! - **(c) name compare** — kept as `&[u8] == &[u8]`, which LLVM already lowers
+//!   to a vectorized `memcmp`; a hand-rolled 8-byte-chunk compare is the same
+//!   instruction sequence, so this is (c) already.
+//!
+//! **(a) mmap is deliberately NOT here and is NOT measurable in this harness:**
+//! `main.rs` does `fs::read` BEFORE `Instant::now()`, so the `mrows_s` metric is
+//! compute-only. mmap is a wall-clock / 13 GB-allocation lever for the full 1B
+//! file, on an axis this timer does not observe. Claiming an mmap speedup on
+//! `mrows_s` would be false; measuring it needs an end-to-end wall-clock mode.
+//!
+//! Reuses lane F's `SoaTable` (flat open-addressed accumulator) verbatim — the
+//! ONLY variable vs lane F is the scan+parse. Same `chunk_bounds`/`merge_maps`
+//! threading. std-only; keeps the crate's zero-dep contract.
+
+use crate::lane_f::{fnv1a64, morton_slot, table_to_map, SoaTable};
+use crate::{chunk_bounds, merge_maps, Stats};
+use std::collections::BTreeMap;
+
+const SEMI_BCAST: u64 = 0x3B3B_3B3B_3B3B_3B3B; // b';' in every byte
+const NL_BCAST: u64 = 0x0A0A_0A0A_0A0A_0A0A; // b'\n' in every byte
+const ONES: u64 = 0x0101_0101_0101_0101;
+const HIGH: u64 = 0x8080_8080_8080_8080;
+
+/// SWAR "has zero byte" applied to `word ^ bcast`: a set 0x80 in each byte
+/// where `word`'s byte equals `bcast`'s byte.
+#[inline(always)]
+fn match_mask(word: u64, bcast: u64) -> u64 {
+    let x = word ^ bcast;
+    x.wrapping_sub(ONES) & !x & HIGH
+}
+
+/// First index `>= i` where `data[idx]` equals `bcast`'s byte — SWAR 8 bytes at
+/// a time, scalar tail. Reads only within `data` (the `i + 8 <= len` guard).
+#[inline(always)]
+fn find(data: &[u8], mut i: usize, bcast: u64) -> usize {
+    let len = data.len();
+    while i + 8 <= len {
+        let word = u64::from_le_bytes(data[i..i + 8].try_into().unwrap());
+        let m = match_mask(word, bcast);
+        if m != 0 {
+            return i + ((m.trailing_zeros() >> 3) as usize);
+        }
+        i += 8;
+    }
+    let b = bcast as u8;
+    while i < len && data[i] != b {
+        i += 1;
+    }
+    i
+}
+
+/// Parse `-?\d?\d.\d` to fixed-point tenths. Branch only on sign and 1-vs-2
+/// integer digits (both perfectly predicted at ~50/50 and ~90/10).
+#[inline(always)]
+fn parse_tenths(s: &[u8]) -> i32 {
+    let neg = s[0] == b'-';
+    let d = if neg { &s[1..] } else { s };
+    let v = if d.len() == 3 {
+        // d.d
+        (d[0] - b'0') as i32 * 10 + (d[2] - b'0') as i32
+    } else {
+        // dd.d
+        (d[0] - b'0') as i32 * 100 + (d[1] - b'0') as i32 * 10 + (d[3] - b'0') as i32
+    };
+    if neg {
+        -v
+    } else {
+        v
+    }
+}
+
+/// Scan `data` with the SWAR find + branchless parse, folding into lane F's
+/// flat `SoaTable`. The ONLY difference from `lane_f::accumulate_table` is the
+/// scan/parse — same hash, same slot fn, same table.
+fn accumulate_swar(data: &[u8]) -> SoaTable {
+    let mut table = SoaTable::new();
+    let len = data.len();
+    let mut i = 0usize;
+    while i < len {
+        let name_start = i;
+        let semi = find(data, i, SEMI_BCAST);
+        let name = &data[name_start..semi];
+        let nl = find(data, semi + 1, NL_BCAST);
+        let tenths = parse_tenths(&data[semi + 1..nl]);
+        let h = fnv1a64(name);
+        table.observe(morton_slot(h), h, name, tenths);
+        i = nl + 1;
+    }
+    table
+}
+
+/// Lane S — SWAR delimiter scan + branchless parse over lane F's flat table.
+pub fn lane_s_swar(data: &[u8], workers: usize) -> BTreeMap<String, Stats> {
+    let workers = workers.max(1);
+    let bounds = chunk_bounds(data, workers);
+    let results: Vec<BTreeMap<String, Stats>> = std::thread::scope(|scope| {
+        let handles: Vec<_> = bounds
+            .iter()
+            .map(|&(start, end)| {
+                let slice = &data[start..end];
+                scope.spawn(move || table_to_map(accumulate_swar(slice)))
+            })
+            .collect();
+        handles
+            .into_iter()
+            .map(|h| h.join().expect("lane S worker panicked"))
+            .collect()
+    });
+    merge_maps(results)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn swar_find_matches_scalar() {
+        let data = b"hello;12.3\nab;-4.5\n";
+        // ';' after "hello" (idx 5), '\n' after "12.3" (idx 10), etc.
+        assert_eq!(find(data, 0, SEMI_BCAST), 5);
+        assert_eq!(find(data, 6, NL_BCAST), 10);
+        assert_eq!(find(data, 11, SEMI_BCAST), 13);
+        assert_eq!(find(data, 14, NL_BCAST), 18);
+    }
+
+    #[test]
+    fn parse_tenths_all_shapes() {
+        assert_eq!(parse_tenths(b"1.0"), 10);
+        assert_eq!(parse_tenths(b"12.3"), 123);
+        assert_eq!(parse_tenths(b"-4.5"), -45);
+        assert_eq!(parse_tenths(b"-99.9"), -999);
+        assert_eq!(parse_tenths(b"0.0"), 0);
+    }
+
+    #[test]
+    fn lane_s_agrees_with_lane_a() {
+        let dir = std::env::temp_dir();
+        let path = dir.join(format!("onebrc_probe_test_s_{}.txt", std::process::id()));
+        let result = crate::gen::gen(&path, 50_000, 97).expect("gen");
+        assert_eq!(result.rows, 50_000);
+        let data = std::fs::read(&path).expect("read generated corpus");
+        std::fs::remove_file(&path).ok();
+
+        let a = crate::lane_a_scalar(&data);
+        let s = lane_s_swar(&data, 3);
+        assert_eq!(a, s, "SWAR lane must produce identical aggregates to lane A");
+        assert!(!a.is_empty());
+    }
+}

crates/onebrc-probe/src/lib.rs

@@ -67,6 +67,7 @@ pub mod lane_j;
 #[cfg(feature = "presets")]
 pub mod presets;
 pub mod sha256;
+pub mod lane_s;
 
 #[cfg(feature = "lane-b")]
 pub use lane_b::lane_b_simd;
@@ -75,6 +76,7 @@ pub use lane_d::lane_d_ractor;
 #[cfg(feature = "lane-e")]
 pub use lane_e::lane_e_kanban;
 pub use lane_f::{lane_f_morton, lane_r_radix};
+pub use lane_s::lane_s_swar;
 #[cfg(feature = "lane-g")]
 pub use lane_g::{lane_g_kanban_soa, lane_g_kanban_soa_with_morsel};
 #[cfg(feature = "lane-h")]

crates/onebrc-probe/src/main.rs

@@ -3,7 +3,7 @@
 //!
 //! ```text
 //! onebrc-probe gen <path> <rows> <seed>
-//! onebrc-probe run <path> <lane:a|b|c|d|e|f|r> [workers] [batches]
+//! onebrc-probe run <path> <lane:a|b|c|d|e|f|r|s> [workers] [batches]
 //! ```
 //!
 //! Lane `b` requires `--features lane-b`; lane `d` and lane `e` require
@@ -23,7 +23,7 @@ fn main() {
         Some("run") => cmd_run(&args[2..]),
         _ => {
             eprintln!(
-                "usage:\n  onebrc-probe gen <path> <rows> <seed>\n  onebrc-probe run <path> <lane:a|b|c|d|e|f|r> [workers] [batches]"
+                "usage:\n  onebrc-probe gen <path> <rows> <seed>\n  onebrc-probe run <path> <lane:a|b|c|d|e|f|r|s> [workers] [batches]"
             );
             std::process::exit(2);
         }
@@ -55,7 +55,7 @@ fn cmd_gen(args: &[String]) {
 fn cmd_run(args: &[String]) {
     let path = PathBuf::from(
         args.first()
-            .expect("usage: run <path> <lane:a|b|c|d|e|f|r> [workers] [batches]"),
+            .expect("usage: run <path> <lane:a|b|c|d|e|f|r|s> [workers] [batches]"),
     );
     let lane = args.get(1).map(String::as_str).unwrap_or("a");
     let workers: usize = args
@@ -132,6 +132,7 @@ fn cmd_run(args: &[String]) {
         // Morton-tile SoA lane and its plain-radix control (lane_f.rs).
         "f" => onebrc_probe::lane_f_morton(&data, workers),
         "r" => onebrc_probe::lane_r_radix(&data, workers),
+        "s" => onebrc_probe::lane_s_swar(&data, workers),
         "g" => {
             #[cfg(feature = "lane-g")]
             {
@@ -200,7 +201,7 @@ fn cmd_run(args: &[String]) {
             }
         }
         other => {
-            eprintln!("unknown lane '{other}' (expected 'a', 'b', 'c', 'd', 'e', 'f', or 'r')");
+            eprintln!("unknown lane '{other}' (expected 'a', 'b', 'c', 'd', 'e', 'f', 'r', or 's')");
             std::process::exit(2);
         }
     };