shuf: perf: Use itoa for integer formatting

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.

.vscode/cspell.dictionaries/workspace.wordlist.txt

@@ -38,6 +38,7 @@ getrandom
 globset
 indicatif
 itertools
+itoa
 iuse
 langid
 lscolors

Cargo.lock

@@ -3867,6 +3867,7 @@ dependencies = [
  "clap",
  "codspeed-divan-compat",
  "fluent",
+ "itoa",
  "rand 0.9.2",
  "rand_core 0.9.5",
  "uucore",

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 = [

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 }

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())
     }
 }