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This commit is contained in:
Giles Cope 2022-04-02 10:28:33 +01:00
parent d27454eda5
commit 4bfea71637
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GPG Key ID: 631F6352D4A949EF
1 changed files with 42 additions and 34 deletions
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76
library/core/src/num/mod.rs
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@ -975,9 +975,9 @@ trait FromStrRadixHelper: PartialOrd + Copy {
fn checked_mul(&self, other: u32) -> Option<Self>;
fn checked_sub(&self, other: u32) -> Option<Self>;
fn checked_add(&self, other: u32) -> Option<Self>;
unsafe fn unchecked_mul(&self, other: u32) -> Self;
unsafe fn unchecked_sub(&self, other: u32) -> Self;
unsafe fn unchecked_add(&self, other: u32) -> Self;
unsafe fn unchecked_mul(self, other: u32) -> Self;
unsafe fn unchecked_sub(self, other: u32) -> Self;
unsafe fn unchecked_add(self, other: u32) -> Self;
}
macro_rules! from_str_radix_int_impl {
@ -993,7 +993,7 @@ macro_rules! from_str_radix_int_impl {
}
from_str_radix_int_impl! { isize i8 i16 i32 i64 i128 usize u8 u16 u32 u64 u128 }
macro_rules! doit {
macro_rules! impl_helper_for {
($($t:ty)*) => ($(impl FromStrRadixHelper for $t {
const MIN: Self = Self::MIN;
#[inline]
@ -1011,29 +1011,29 @@ macro_rules! doit {
Self::checked_add(*self, other as Self)
}
#[inline]
unsafe fn unchecked_mul(&self, other: u32) -> Self {
unsafe fn unchecked_mul(self, other: u32) -> Self {
// SAFETY: Conditions of `Self::unchecked_mul` must be upheld by the caller.
unsafe {
Self::unchecked_mul(*self, other as Self)
Self::unchecked_mul(self, other as Self)
}
}
#[inline]
unsafe fn unchecked_sub(&self, other: u32) -> Self {
unsafe fn unchecked_sub(self, other: u32) -> Self {
// SAFETY: Conditions of `Self::unchecked_sub` must be upheld by the caller.
unsafe {
Self::unchecked_sub(*self, other as Self)
Self::unchecked_sub(self, other as Self)
}
}
#[inline]
unsafe fn unchecked_add(&self, other: u32) -> Self {
unsafe fn unchecked_add(self, other: u32) -> Self {
// SAFETY: Conditions of `Self::unchecked_add` must be upheld by the caller.
unsafe {
Self::unchecked_add(*self, other as Self)
Self::unchecked_add(self, other as Self)
}
}
})*)
}
doit! { i8 i16 i32 i64 i128 isize u8 u16 u32 u64 u128 usize }
impl_helper_for! { i8 i16 i32 i64 i128 isize u8 u16 u32 u64 u128 usize }
fn from_str_radix<T: FromStrRadixHelper>(src: &str, radix: u32) -> Result<T, ParseIntError> {
use self::IntErrorKind::*;
@ -1078,41 +1078,49 @@ fn from_str_radix<T: FromStrRadixHelper>(src: &str, radix: u32) -> Result<T, Par
// `u8::MAX` is `ff` - any str of len 2 is guaranteed to not overflow.
// `i8::MAX` is `7f` - only a str of len 1 is guaranteed to not overflow.
unsafe {
macro_rules! run_loop {
macro_rules! run_unchecked_loop {
($unchecked_additive_op:ident) => {
for &c in digits {
result = result.unchecked_mul(radix);
let x = (c as char).to_digit(radix).ok_or(PIE { kind: InvalidDigit })?;
result = T::$unchecked_additive_op(&result, x);
result = T::$unchecked_additive_op(result, x);
}
};
}
if is_positive {
run_loop!(unchecked_add)
run_unchecked_loop!(unchecked_add)
} else {
run_loop!(unchecked_sub)
run_unchecked_loop!(unchecked_sub)
};
}
} else {
let additive_op = if is_positive { T::checked_add } else { T::checked_sub };
let overflow_err = || PIE { kind: if is_positive { PosOverflow } else { NegOverflow } };
for &c in digits {
// When `radix` is passed in as a literal, rather than doing a slow `imul`
// the compiler can use shifts if `radix` can be expressed as a
// sum of powers of 2 (x*10 can be written as x*8 + x*2).
// When the compiler can't use these optimisations,
// the latency of the multiplication can be hidden by issuing it
// before the result is needed to improve performance on
// modern out-of-order CPU as multiplication here is slower
// than the other instructions, we can get the end result faster
// doing multiplication first and let the CPU spends other cycles
// doing other computation and get multiplication result later.
let mul = result.checked_mul(radix);
let x = (c as char).to_digit(radix).ok_or(PIE { kind: InvalidDigit })?;
result = mul.ok_or_else(overflow_err)?;
result = additive_op(&result, x).ok_or_else(overflow_err)?;
} else {
macro_rules! run_checked_loop {
($checked_additive_op:ident, $overflow_err:ident) => {
for &c in digits {
// When `radix` is passed in as a literal, rather than doing a slow `imul`
// the compiler can use shifts if `radix` can be expressed as a
// sum of powers of 2 (x*10 can be written as x*8 + x*2).
// When the compiler can't use these optimisations,
// the latency of the multiplication can be hidden by issuing it
// before the result is needed to improve performance on
// modern out-of-order CPU as multiplication here is slower
// than the other instructions, we can get the end result faster
// doing multiplication first and let the CPU spends other cycles
// doing other computation and get multiplication result later.
let mul = result.checked_mul(radix);
let x = (c as char).to_digit(radix).ok_or(PIE { kind: InvalidDigit })?;
result = mul.ok_or_else($overflow_err)?;
result = T::$checked_additive_op(&result, x).ok_or_else($overflow_err)?;
}
}
}
if is_positive {
let overflow_err = || PIE { kind: PosOverflow };
run_checked_loop!(checked_add, overflow_err)
} else {
let overflow_err = || PIE { kind: NegOverflow };
run_checked_loop!(checked_sub, overflow_err)
};
}
Ok(result)
}