From 3017ddad9e94bdb2d7dadc91c5e20758cffb5a5f Mon Sep 17 00:00:00 2001
From: Jan Verbeek <jan.verbeek@posteo.nl>
Date: Wed, 26 Mar 2025 10:34:54 +0100
Subject: [PATCH] shuf: perf: Use itoa for integer formatting
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This gives a 1.8× speedup over a stdlib formatted write for
`shuf -r -n1000000 -i1-1024`.

The original version of this commit replaced a formatted write, but
before it got merged main received optimized manual formatting from
another PR. The speedup of itoa over the manual write is around 1.1×,
much less dramatic.
---
 .../workspace.wordlist.txt                    |  1 +
 Cargo.lock                                    |  1 +
 Cargo.toml                                    |  1 +
 src/uu/shuf/Cargo.toml                        |  1 +
 src/uu/shuf/src/shuf.rs                       | 24 ++++---------------
 5 files changed, 8 insertions(+), 20 deletions(-)

diff --git a/.vscode/cspell.dictionaries/workspace.wordlist.txt b/.vscode/cspell.dictionaries/workspace.wordlist.txt
index 28c468d4f..30d2bd3e0 100644
--- a/.vscode/cspell.dictionaries/workspace.wordlist.txt
+++ b/.vscode/cspell.dictionaries/workspace.wordlist.txt
@@ -38,6 +38,7 @@ getrandom
 globset
 indicatif
 itertools
+itoa
 iuse
 langid
 lscolors
diff --git a/Cargo.lock b/Cargo.lock
index 5450edf53..c5e5d61dd 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3867,6 +3867,7 @@ dependencies = [
  "clap",
  "codspeed-divan-compat",
  "fluent",
+ "itoa",
  "rand 0.9.2",
  "rand_core 0.9.5",
  "uucore",
diff --git a/Cargo.toml b/Cargo.toml
index 2f57496a5..d3eee72cc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -335,6 +335,7 @@ icu_locale = "2.0.0"
 icu_provider = "2.0.0"
 indicatif = "0.18.0"
 itertools = "0.14.0"
+itoa = "1.0.15"
 jiff = "0.2.18"
 libc = "0.2.172"
 lscolors = { version = "0.21.0", default-features = false, features = [
diff --git a/src/uu/shuf/Cargo.toml b/src/uu/shuf/Cargo.toml
index 26a270b88..135dc29f4 100644
--- a/src/uu/shuf/Cargo.toml
+++ b/src/uu/shuf/Cargo.toml
@@ -19,6 +19,7 @@ path = "src/shuf.rs"
 
 [dependencies]
 clap = { workspace = true }
+itoa = { workspace = true }
 rand = { workspace = true }
 rand_core = { workspace = true }
 uucore = { workspace = true }
diff --git a/src/uu/shuf/src/shuf.rs b/src/uu/shuf/src/shuf.rs
index 1cc444283..cc04a3068 100644
--- a/src/uu/shuf/src/shuf.rs
+++ b/src/uu/shuf/src/shuf.rs
@@ -340,26 +340,10 @@ impl Writable for &OsStr {
 
 impl Writable for usize {
     fn write_all_to(&self, output: &mut impl OsWrite) -> Result<(), Error> {
-        let mut n = *self;
-
-        // Handle the zero case explicitly
-        if n == 0 {
-            return output.write_all(b"0");
-        }
-
-        // Maximum number of digits for u64 is 20 (18446744073709551615)
-        let mut buf = [0u8; 20];
-        let mut i = 20;
-
-        // Write digits from right to left
-        while n > 0 {
-            i -= 1;
-            buf[i] = b'0' + (n % 10) as u8;
-            n /= 10;
-        }
-
-        // Write the relevant part of the buffer to output
-        output.write_all(&buf[i..])
+        // The itoa crate is surprisingly much more efficient than a formatted write.
+        // It speeds up `shuf -r -n1000000 -i1-1024` by 1.8×.
+        let mut buf = itoa::Buffer::new();
+        output.write_all(buf.format(*self).as_bytes())
     }
 }