uucore: format: Use ExtendedBigDecimal in argument code

Provides arbitrary precision for float parsing in printf.

Also add a printf test for that.

src/uucore/src/lib/features/format/argument.rs

@@ -12,6 +12,8 @@ use crate::{
 use os_display::Quotable;
 use std::ffi::OsStr;
 
+use super::ExtendedBigDecimal;
+
 /// An argument for formatting
 ///
 /// Each of these variants is only accepted by their respective directives. For
@@ -25,7 +27,7 @@ pub enum FormatArgument {
     String(String),
     UnsignedInt(u64),
     SignedInt(i64),
-    Float(f64),
+    Float(ExtendedBigDecimal),
     /// Special argument that gets coerced into the other variants
     Unparsed(String),
 }
@@ -34,7 +36,7 @@ pub trait ArgumentIter<'a>: Iterator<Item = &'a FormatArgument> {
     fn get_char(&mut self) -> u8;
     fn get_i64(&mut self) -> i64;
     fn get_u64(&mut self) -> u64;
-    fn get_f64(&mut self) -> f64;
+    fn get_extended_big_decimal(&mut self) -> ExtendedBigDecimal;
     fn get_str(&mut self) -> &'a str;
 }
 
@@ -72,14 +74,14 @@ impl<'a, T: Iterator<Item = &'a FormatArgument>> ArgumentIter<'a> for T {
         }
     }
 
-    fn get_f64(&mut self) -> f64 {
+    fn get_extended_big_decimal(&mut self) -> ExtendedBigDecimal {
         let Some(next) = self.next() else {
-            return 0.0;
+            return ExtendedBigDecimal::zero();
         };
         match next {
-            FormatArgument::Float(n) => *n,
-            FormatArgument::Unparsed(s) => extract_value(f64::extended_parse(s), s),
-            _ => 0.0,
+            FormatArgument::Float(n) => n.clone(),
+            FormatArgument::Unparsed(s) => extract_value(ExtendedBigDecimal::extended_parse(s), s),
+            _ => ExtendedBigDecimal::zero(),
         }
     }
 

src/uucore/src/lib/features/format/extendedbigdecimal.rs

@@ -141,6 +141,12 @@ impl Zero for ExtendedBigDecimal {
     }
 }
 
+impl Default for ExtendedBigDecimal {
+    fn default() -> Self {
+        Self::zero()
+    }
+}
+
 impl Add for ExtendedBigDecimal {
     type Output = Self;
 

src/uucore/src/lib/features/format/spec.rs

@@ -433,8 +433,7 @@ impl Spec {
             } => {
                 let width = resolve_asterisk(*width, &mut args).unwrap_or(0);
                 let precision = resolve_asterisk(*precision, &mut args).unwrap_or(6);
-                // TODO: We should implement some get_extendedBigDecimal function in args to avoid losing precision.
-                let f: ExtendedBigDecimal = args.get_f64().into();
+                let f: ExtendedBigDecimal = args.get_extended_big_decimal();
 
                 if precision as u64 > i32::MAX as u64 {
                     return Err(FormatError::InvalidPrecision(precision.to_string()));

tests/by-util/test_printf.rs

@@ -992,6 +992,16 @@ fn float_flag_position_space_padding() {
         .stdout_only(" +1.0");
 }
 
+#[test]
+fn float_large_precision() {
+    // Note: This does not match GNU coreutils output (0.100000000000000000001355252716 on x86),
+    // as we parse and format using ExtendedBigDecimal, which provides arbitrary precision.
+    new_ucmd!()
+        .args(&["%.30f", "0.1"])
+        .succeeds()
+        .stdout_only("0.100000000000000000000000000000");
+}
+
 #[test]
 fn float_non_finite_space_padding() {
     new_ucmd!()