From f33e058a5a3af79ee5ca7654aa2a0f372b75ae0a Mon Sep 17 00:00:00 2001
From: Justin Tracey <j2tracey@gmail.com>
Date: Sun, 6 Feb 2022 02:17:25 -0500
Subject: [PATCH] join: faster field parsing and representation

Using indexes into the line instead of Vec<u8>s means we don't have to copy
the line to store the fields (indexes instead of slices because it avoids
self-referential structs). Using memchr also empirically saves a lot of
intermediate allocations.
---
 Cargo.lock              |  1 +
 src/uu/join/Cargo.toml  |  1 +
 src/uu/join/src/join.rs | 58 +++++++++++++++++++++++++----------------
 3 files changed, 37 insertions(+), 23 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index cc7c3967b..b1c374651 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2444,6 +2444,7 @@ name = "uu_join"
 version = "0.0.12"
 dependencies = [
  "clap 3.0.10",
+ "memchr 2.4.1",
  "uucore",
 ]
 
diff --git a/src/uu/join/Cargo.toml b/src/uu/join/Cargo.toml
index b4150b4be..2a03fe002 100644
--- a/src/uu/join/Cargo.toml
+++ b/src/uu/join/Cargo.toml
@@ -17,6 +17,7 @@ path = "src/join.rs"
 [dependencies]
 clap = { version = "3.0", features = ["wrap_help", "cargo"] }
 uucore = { version=">=0.0.11", package="uucore", path="../../uucore" }
+memchr = "2"
 
 [[bin]]
 name = "join"
diff --git a/src/uu/join/src/join.rs b/src/uu/join/src/join.rs
index cb953c133..dcd699438 100644
--- a/src/uu/join/src/join.rs
+++ b/src/uu/join/src/join.rs
@@ -11,6 +11,7 @@
 extern crate uucore;
 
 use clap::{crate_version, App, AppSettings, Arg};
+use memchr::{memchr3_iter, memchr_iter};
 use std::cmp::Ordering;
 use std::convert::From;
 use std::error::Error;
@@ -66,7 +67,7 @@ enum LineEnding {
     Newline = b'\n',
 }
 
-#[derive(Copy, Clone)]
+#[derive(Copy, Clone, PartialEq)]
 enum Sep {
     Char(u8),
     Line,
@@ -147,7 +148,7 @@ impl<'a> Repr<'a> {
     fn print_field(
         &self,
         writer: &mut impl Write,
-        field: Option<&Vec<u8>>,
+        field: Option<&[u8]>,
     ) -> Result<(), std::io::Error> {
         let value = match field {
             Some(field) => field,
@@ -164,10 +165,10 @@ impl<'a> Repr<'a> {
         line: &Line,
         index: usize,
     ) -> Result<(), std::io::Error> {
-        for i in 0..line.fields.len() {
+        for i in 0..line.field_ranges.len() {
             if i != index {
                 writer.write_all(&[self.separator])?;
-                writer.write_all(&line.fields[i])?;
+                writer.write_all(line.get_field(i).unwrap())?;
             }
         }
         Ok(())
@@ -176,7 +177,7 @@ impl<'a> Repr<'a> {
     /// Print each field or the empty filler if the field is not set.
     fn print_format<F>(&self, writer: &mut impl Write, f: F) -> Result<(), std::io::Error>
     where
-        F: Fn(&Spec) -> Option<&'a Vec<u8>>,
+        F: Fn(&Spec) -> Option<&'a [u8]>,
     {
         for i in 0..self.format.len() {
             if i > 0 {
@@ -214,7 +215,7 @@ impl Input {
         }
     }
 
-    fn compare(&self, field1: Option<&Vec<u8>>, field2: Option<&Vec<u8>>) -> Ordering {
+    fn compare(&self, field1: Option<&[u8]>, field2: Option<&[u8]>) -> Ordering {
         if let (Some(field1), Some(field2)) = (field1, field2) {
             if self.ignore_case {
                 field1
@@ -277,30 +278,41 @@ impl Spec {
 }
 
 struct Line {
-    fields: Vec<Vec<u8>>,
+    field_ranges: Vec<(usize, usize)>,
     string: Vec<u8>,
 }
 
 impl Line {
     fn new(string: Vec<u8>, separator: Sep) -> Self {
-        let fields = match separator {
-            Sep::Whitespaces => string
-                // GNU join uses Bourne shell field splitters by default
-                .split(|c| matches!(*c, b' ' | b'\t' | b'\n'))
-                .filter(|f| !f.is_empty())
-                .map(Vec::from)
-                .collect(),
-            Sep::Char(sep) => string.split(|c| *c == sep).map(Vec::from).collect(),
-            Sep::Line => vec![string.clone()],
-        };
+        let mut field_ranges = Vec::new();
+        let mut last_end = 0;
+        if separator == Sep::Whitespaces {
+            // GNU join uses Bourne shell field splitters by default
+            for i in memchr3_iter(b' ', b'\t', b'\n', &string) {
+                if i > last_end {
+                    field_ranges.push((last_end, i));
+                }
+                last_end = i + 1;
+            }
+        } else if let Sep::Char(sep) = separator {
+            for i in memchr_iter(sep, &string) {
+                field_ranges.push((last_end, i));
+                last_end = i + 1;
+            }
+        }
+        field_ranges.push((last_end, string.len()));
 
-        Self { fields, string }
+        Self {
+            field_ranges,
+            string,
+        }
     }
 
     /// Get field at index.
-    fn get_field(&self, index: usize) -> Option<&Vec<u8>> {
-        if index < self.fields.len() {
-            Some(&self.fields[index])
+    fn get_field(&self, index: usize) -> Option<&[u8]> {
+        if index < self.field_ranges.len() {
+            let (low, high) = self.field_ranges[index];
+            Some(&self.string[low..high])
         } else {
             None
         }
@@ -470,7 +482,7 @@ impl<'a> State<'a> {
             self.seq.push(line);
 
             if autoformat {
-                return self.seq[0].fields.len();
+                return self.seq[0].field_ranges.len();
             }
         }
         0
@@ -547,7 +559,7 @@ impl<'a> State<'a> {
     }
 
     /// Gets the key value of the lines stored in seq.
-    fn get_current_key(&self) -> Option<&Vec<u8>> {
+    fn get_current_key(&self) -> Option<&[u8]> {
         self.seq[0].get_field(self.key)
     }