seq: replace loops with a single format string

Replace two loops that print leading and trailing 0s when printing a
number in fixed-width mode with a single call to `write!()` with the
appropriate formatting parameters.

src/uu/seq/src/seq.rs

@@ -317,6 +317,7 @@ fn print_seq(
     let mut i = 0isize;
     let is_first_minus_zero = first == -0.0 && first.is_sign_negative();
     let mut value = first + i as f64 * increment;
+    let padding = if pad { padding + 1 + largest_dec } else { 0 };
     let mut is_first_iteration = true;
     while !done_printing(&value, &increment, &last) {
         if !is_first_iteration {
@@ -328,15 +329,13 @@ fn print_seq(
             width -= 1;
         }
         is_first_iteration = false;
-        let istr = format!("{:.*}", largest_dec, value);
-        let ilen = istr.len();
-        let before_dec = istr.find('.').unwrap_or(ilen);
-        if pad && before_dec < width {
-            for _ in 0..(width - before_dec) {
-                write!(stdout, "0")?;
-            }
-        }
-        write!(stdout, "{}", istr)?;
+        write!(
+            stdout,
+            "{value:>0width$.precision$}",
+            value = value,
+            width = width,
+            precision = largest_dec,
+        )?;
         i += 1;
         value = first + i as f64 * increment;
     }

tests/by-util/test_seq.rs

@@ -426,6 +426,15 @@ fn test_width_decimal_scientific_notation_trailing_zeros_end() {
         .no_stderr();
 }
 
+#[test]
+fn test_width_floats() {
+    new_ucmd!()
+        .args(&["-w", "9.0", "10.0"])
+        .succeeds()
+        .stdout_is("09.0\n10.0\n")
+        .no_stderr();
+}
+
 // TODO This is duplicated from `test_yes.rs`; refactor them.
 /// Run `seq`, capture some of the output, close the pipe, and verify it.
 fn run(args: &[&str], expected: &[u8]) {