remove the wrapping arithmetics

src/libcore/fmt/mod.rs

@@ -274,16 +274,12 @@ impl<'a> Arguments<'a> {
  #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
  issue = "0")]
  pub fn estimated_capacity(&self) -> usize {
- // Using wrapping arithmetics in this function, because
- // wrong result is highly unlikely and doesn't cause unsafety.
- use ::num::Wrapping as W;
-
- let pieces_length: W<usize> = self.pieces.iter()
- .map(|x| W(x.len())).sum();
+ let pieces_length: usize = self.pieces.iter()
+ .map(|x| x.len()).sum();
 
  if self.args.is_empty() {
- pieces_length.0
- } else if self.pieces[0] == "" && pieces_length < W(16) {
+ pieces_length
+ } else if self.pieces[0] == "" && pieces_length < 16 {
  // If the format string starts with an argument,
  // don't preallocate anything, unless length
  // of pieces is significant.
@@ -292,9 +288,8 @@ impl<'a> Arguments<'a> {
  // There are some arguments, so any additional push
  // will reallocate the string. To avoid that,
  // we're "pre-doubling" the capacity here.
- (pieces_length * W(2)).0
+ pieces_length.checked_mul(2).unwrap_or(0)
  }
-
  }
 }