diff options
Diffstat (limited to 'vendor/writeable/src/impls.rs')
| -rw-r--r-- | vendor/writeable/src/impls.rs | 104 |
1 files changed, 55 insertions, 49 deletions
diff --git a/vendor/writeable/src/impls.rs b/vendor/writeable/src/impls.rs index 649ede4d5..a2b5201e0 100644 --- a/vendor/writeable/src/impls.rs +++ b/vendor/writeable/src/impls.rs @@ -7,12 +7,12 @@ use alloc::borrow::Cow; use core::fmt; macro_rules! impl_write_num { - ($u:ty, $i:ty, $test:ident, $log10:ident) => { + ($u:ty, $i:ty, $test:ident, $max_ilog_10:expr) => { impl $crate::Writeable for $u { fn write_to<W: core::fmt::Write + ?Sized>(&self, sink: &mut W) -> core::fmt::Result { - let mut buf = [b'0'; $log10(<$u>::MAX) as usize + 1]; + let mut buf = [b'0'; $max_ilog_10 + 1]; let mut n = *self; - let mut i = buf.len(); + let mut i = $max_ilog_10 + 1; #[allow(clippy::indexing_slicing)] // n < 10^i while n != 0 { i -= 1; @@ -29,40 +29,38 @@ macro_rules! impl_write_num { } fn writeable_length_hint(&self) -> $crate::LengthHint { - $crate::LengthHint::exact(if *self == 0 { - 1 - } else { - $log10(*self) as usize + 1 - }) + LengthHint::exact(self.checked_ilog10().unwrap_or(0) as usize + 1) } } - // TODO: use the library functions once stabilized. - // https://github.com/unicode-org/icu4x/issues/1428 - #[inline] - const fn $log10(s: $u) -> u32 { - let b = (<$u>::BITS - 1) - s.leading_zeros(); - // s ∈ [2ᵇ, 2ᵇ⁺¹-1] => ⌊log₁₀(s)⌋ ∈ [⌊log₁₀(2ᵇ)⌋, ⌊log₁₀(2ᵇ⁺¹-1)⌋] - // <=> ⌊log₁₀(s)⌋ ∈ [⌊log₁₀(2ᵇ)⌋, ⌊log₁₀(2ᵇ⁺¹)⌋] - // <=> ⌊log₁₀(s)⌋ ∈ [⌊b log₁₀(2)⌋, ⌊(b+1) log₁₀(2)⌋] - // The second line holds because there is no integer in - // [log₁₀(2ᶜ-1), log₁₀(2ᶜ)], if there were, there'd be some 10ⁿ in - // [2ᶜ-1, 2ᶜ], but it can't be 2ᶜ-1 due to parity nor 2ᶜ due to prime - // factors. - - const M: u32 = (core::f64::consts::LOG10_2 * (1 << 26) as f64) as u32; - let low = (b * M) >> 26; - let high = ((b + 1) * M) >> 26; - - // If the bounds aren't tight (e.g. 87 ∈ [64, 127] ⟹ ⌊log₁₀(87)⌋ ∈ [1,2]), - // compare to 10ʰ (100). This shouldn't happen too often as there are more - // powers of 2 than 10 (it happens for 14% of u32s). - if high == low { - low - } else if s < (10 as $u).pow(high) { - low - } else { - high + impl ILog10Ext for $u { + fn checked_ilog10(self) -> Option<u32> { + if self == 0 { + return None; + } + let b = (<$u>::BITS - 1) - self.leading_zeros(); + // self ∈ [2ᵇ, 2ᵇ⁺¹-1] => ⌊log₁₀(self)⌋ ∈ [⌊log₁₀(2ᵇ)⌋, ⌊log₁₀(2ᵇ⁺¹-1)⌋] + // <=> ⌊log₁₀(self)⌋ ∈ [⌊log₁₀(2ᵇ)⌋, ⌊log₁₀(2ᵇ⁺¹)⌋] + // <=> ⌊log₁₀(self)⌋ ∈ [⌊b log₁₀(2)⌋, ⌊(b+1) log₁₀(2)⌋] + // The second line holds because there is no integer in + // [log₁₀(2ᶜ-1), log₁₀(2ᶜ)], if there were, there'd be some 10ⁿ in + // [2ᶜ-1, 2ᶜ], but it can't be 2ᶜ-1 due to parity nor 2ᶜ due to prime + // factors. + + const M: u32 = (core::f64::consts::LOG10_2 * (1 << 26) as f64) as u32; + let low = (b * M) >> 26; + let high = ((b + 1) * M) >> 26; + + // If the bounds aren't tight (e.g. 87 ∈ [64, 127] ⟹ ⌊log₁₀(87)⌋ ∈ [1,2]), + // compare to 10ʰ (100). This shouldn't happen too often as there are more + // powers of 2 than 10 (it happens for 14% of u32s). + Some(if high == low { + low + } else if self < (10 as $u).pow(high) { + low + } else { + high + }) } } @@ -84,11 +82,14 @@ macro_rules! impl_write_num { fn $test() { use $crate::assert_writeable_eq; assert_writeable_eq!(&(0 as $u), "0"); - assert_writeable_eq!(&(0 as $u), "0"); + assert_writeable_eq!(&(0 as $i), "0"); assert_writeable_eq!(&(-0 as $i), "0"); assert_writeable_eq!(&(1 as $u), "1"); assert_writeable_eq!(&(1 as $i), "1"); assert_writeable_eq!(&(-1 as $i), "-1"); + assert_writeable_eq!(&(9 as $u), "9"); + assert_writeable_eq!(&(9 as $i), "9"); + assert_writeable_eq!(&(-9 as $i), "-9"); assert_writeable_eq!(&(10 as $u), "10"); assert_writeable_eq!(&(10 as $i), "10"); assert_writeable_eq!(&(-10 as $i), "-10"); @@ -112,19 +113,24 @@ macro_rules! impl_write_num { }; } -impl_write_num!(u8, i8, test_u8, log10_u8); -impl_write_num!(u16, i16, test_u16, log10_u16); -impl_write_num!(u32, i32, test_u32, log10_u32); -impl_write_num!(u64, i64, test_u64, log10_u64); -impl_write_num!(u128, i128, test_u128, log10_u128); - -#[test] -fn assert_log10_approximation() { - for i in 1..u128::BITS { - assert_eq!(i * 59 / 196, 2f64.powf(i.into()).log10().floor() as u32); - } +/// `checked_ilog10` is added as a method on integer types in 1.67. +/// This extension trait provides it for older compilers. +trait ILog10Ext: Sized { + fn checked_ilog10(self) -> Option<u32>; } +impl_write_num!(u8, i8, test_u8, 2); +impl_write_num!(u16, i16, test_u16, 4); +impl_write_num!(u32, i32, test_u32, 9); +impl_write_num!(u64, i64, test_u64, 19); +impl_write_num!(u128, i128, test_u128, 38); +impl_write_num!( + usize, + isize, + test_usize, + if usize::MAX as u64 == u64::MAX { 19 } else { 9 } +); + impl Writeable for str { #[inline] fn write_to<W: fmt::Write + ?Sized>(&self, sink: &mut W) -> fmt::Result { @@ -194,7 +200,7 @@ impl<'a, T: Writeable + ?Sized> Writeable for &T { #[test] fn test_string_impls() { - fn check_writeable_slice<W: Writeable>(writeables: &[W]) { + fn check_writeable_slice<W: Writeable + core::fmt::Display>(writeables: &[W]) { assert_writeable_eq!(&writeables[0], ""); assert_writeable_eq!(&writeables[1], "abc"); } @@ -204,10 +210,10 @@ fn test_string_impls() { check_writeable_slice(arr); // test String impl - let arr: &[String] = &["".to_string(), "abc".to_string()]; + let arr: &[String] = &[String::new(), "abc".to_owned()]; check_writeable_slice(arr); // test &T impl - let arr: &[&String] = &[&"".to_string(), &"abc".to_string()]; + let arr: &[&String] = &[&String::new(), &"abc".to_owned()]; check_writeable_slice(arr); } |