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from_u32(0) can just be default()

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This commit is contained in:
Giles Cope
2022-04-04 15:53:53 +01:00
parent 72a5e7e810
commit 82e9d9ebac
3 changed files with 57 additions and 16 deletions
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25
library/core/src/num/mod.rs
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@@ -969,9 +969,8 @@ pub enum FpCategory {
}
#[doc(hidden)]
trait FromStrRadixHelper: PartialOrd + Copy {
trait FromStrRadixHelper: PartialOrd + Copy + Default {
const MIN: Self;
fn from_u32(u: u32) -> Self;
fn checked_mul(&self, other: u32) -> Option<Self>;
fn checked_sub(&self, other: u32) -> Option<Self>;
fn checked_add(&self, other: u32) -> Option<Self>;
@@ -997,8 +996,6 @@ macro_rules! impl_helper_for {
($($t:ty)*) => ($(impl FromStrRadixHelper for $t {
const MIN: Self = Self::MIN;
#[inline]
fn from_u32(u: u32) -> Self { u as Self }
#[inline]
fn checked_mul(&self, other: u32) -> Option<Self> {
Self::checked_mul(*self, other as Self)
}
@@ -1035,8 +1032,14 @@ macro_rules! impl_helper_for {
}
impl_helper_for! { i8 i16 i32 i64 i128 isize u8 u16 u32 u64 u128 usize }
/// Determins if a string of text of that length of that radix could be guaranteed to be
/// stored in the given type T.
/// Note that if the radix is known to the compiler, it is just the check of digits.len that
/// is done at runtime.
#[doc(hidden)]
#[inline(always)]
pub(crate) fn can_not_overflow<T>(radix: u32, is_signed_ty: bool, digits:&[u8]) -> bool {
#[unstable(issue = "none", feature = "std_internals")]
pub fn can_not_overflow<T>(radix: u32, is_signed_ty: bool, digits: &[u8]) -> bool {
radix <= 16 && digits.len() <= mem::size_of::<T>() * 2 - is_signed_ty as usize
}
@@ -1054,7 +1057,7 @@ fn from_str_radix<T: FromStrRadixHelper>(src: &str, radix: u32) -> Result<T, Par
return Err(PIE { kind: Empty });
}
let is_signed_ty = T::from_u32(0) > T::MIN;
let is_signed_ty = T::default() > T::MIN;
// all valid digits are ascii, so we will just iterate over the utf8 bytes
// and cast them to chars. .to_digit() will safely return None for anything
@@ -1071,7 +1074,7 @@ fn from_str_radix<T: FromStrRadixHelper>(src: &str, radix: u32) -> Result<T, Par
_ => (true, src),
};
let mut result = T::from_u32(0);
let mut result = T::default();
if can_not_overflow::<T>(radix, is_signed_ty, digits) {
// SAFETY: If the len of the str is short compared to the range of the type
@@ -1127,11 +1130,3 @@ fn from_str_radix<T: FromStrRadixHelper>(src: &str, radix: u32) -> Result<T, Par
}
Ok(result)
}
mod tests {
#[test]
fn test_can_not_overflow() {
assert_eq!(can_not_overflow::<i8>(10, true, "99".as_bytes()), true);
assert_eq!(can_not_overflow::<i8>(10, true, "129".as_bytes()), false);
}
}