wc: skip String to measure number length

Sadly ilog10 isn't available until we use 1.67, but we can get close in
the meantime.

src/uu/wc/src/wc.rs

@@ -5,7 +5,7 @@
 //  * For the full copyright and license information, please view the LICENSE
 //  * file that was distributed with this source code.
 
-// cSpell:ignore wc wc's
+// cSpell:ignore ilog wc wc's
 
 mod count_fast;
 mod countable;
@@ -632,7 +632,14 @@ fn compute_number_width(inputs: &[Input], settings: &Settings) -> usize {
         }
     }
 
-    max(minimum_width, total.to_string().len())
+    if total == 0 {
+        minimum_width
+    } else {
+        let total_width = (1 + ilog10_u64(total))
+            .try_into()
+            .expect("ilog of a u64 should fit into a usize");
+        max(total_width, minimum_width)
+    }
 }
 
 fn wc(inputs: &[Input], settings: &Settings) -> UResult<()> {
@@ -712,3 +719,29 @@ fn print_stats(
         writeln!(stdout)
     }
 }
+
+// TODO: remove and just use usize::ilog10 once the MSRV is >= 1.67.
+fn ilog10_u64(mut u: u64) -> u32 {
+    if u == 0 {
+        panic!("cannot compute log of 0")
+    }
+    let mut log = 0;
+    if u >= 10_000_000_000 {
+        log += 10;
+        u /= 10_000_000_000;
+    }
+    if u >= 100_000 {
+        log += 5;
+        u /= 100_000;
+    }
+    // Rust's standard library in versions >= 1.67 does something even more clever than this, but
+    // this should work just fine for the time being.
+    log + match u {
+        1..=9 => 0,
+        10..=99 => 1,
+        100..=999 => 2,
+        1000..=9999 => 3,
+        10000..=99999 => 4,
+        _ => unreachable!(),
+    }
+}