diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs index 1cdfa39cd79..714c24a7665 100644 --- a/library/alloc/src/string.rs +++ b/library/alloc/src/string.rs @@ -2224,7 +2224,7 @@ impl ToString for char { } } -#[stable(feature = "u8_to_string_specialization", since="1.999.0")] +#[stable(feature = "u8_to_string_specialization", since = "1.999.0")] impl ToString for u8 { #[inline] fn to_string(&self) -> String { @@ -2243,6 +2243,39 @@ impl ToString for u8 { } } +// 2 digit decimal look up table +static DEC_DIGITS_LUT: &[u8; 200] = b"0001020304050607080910111213141516171819\ + 2021222324252627282930313233343536373839\ + 4041424344454647484950515253545556575859\ + 6061626364656667686970717273747576777879\ + 8081828384858687888990919293949596979899"; + +#[stable(feature = "i8_to_string_specialization", since = "1.999.0")] +impl ToString for i8 { + #[inline] + fn to_string(&self) -> String { + let mut vec: Vec = if *self < 0 { + let mut v = Vec::with_capacity(4); + v.push(b'-'); + v + } else { + Vec::with_capacity(3) + }; + let mut n = self.abs(); + if n >= 10 { + if n >= 100 { + n -= 100; + vec.push(b'1'); + } + let nn = n * 2; + vec.extend_from_slice(&DEC_DIGITS_LUT[nn as usize..=nn as usize + 1]); + } else { + vec.push(b'0' + (n as u8)); + } + unsafe { String::from_utf8_unchecked(vec) } + } +} + #[stable(feature = "str_to_string_specialization", since = "1.9.0")] impl ToString for str { #[inline]