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Rollup merge of #68978 - ecstatic-morse:const-int-pow, r=oli-obk

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Make integer exponentiation methods unstably const

cc #53718

This makes the following inherent methods on integer primitives into unstable `const fn`:
- `pow`
- `checked_pow`
- `wrapping_pow`
- `overflowing_pow`
- `saturating_pow`
- `next_power_of_two`
- `checked_next_power_of_two`
- `wrapping_next_power_of_two`

Only two changes were made to the implementation of these methods. First, I had to switch from the `?` operator, which is not yet implemented in a const context, to a `try_opt` macro. Second, `next_power_of_two` was using `ops::Add::add` (see the first commit) to "get overflow checks", so I switched to `#[rustc_inherit_overflow_checks]`. I'm not quite sure why the attribute wasn't used in the first place.
This commit is contained in:
Dylan DPC 2020-02-20 10:49:12 +01:00 committed by GitHub
commit d96951f554
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3 changed files with 86 additions and 23 deletions
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3
src/libcore/lib.rs
View File

@ -73,11 +73,14 @@
#![feature(const_ascii_ctype_on_intrinsics)]
#![feature(const_alloc_layout)]
#![feature(const_if_match)]
#![feature(const_loop)]
#![feature(const_checked_int_methods)]
#![feature(const_euclidean_int_methods)]
#![feature(const_overflowing_int_methods)]
#![feature(const_saturating_int_methods)]
#![feature(const_int_unchecked_arith)]
#![feature(const_int_pow)]
#![feature(constctlz)]
#![feature(const_panic)]
#![feature(const_fn_union)]
#![feature(const_generics)]

69
src/libcore/num/mod.rs
View File

@ -8,9 +8,18 @@ use crate::convert::Infallible;
use crate::fmt;
use crate::intrinsics;
use crate::mem;
use crate::ops;
use crate::str::FromStr;
// Used because the `?` operator is not allowed in a const context.
macro_rules! try_opt {
($e:expr) => {
match $e {
Some(x) => x,
None => return None,
}
};
}
macro_rules! impl_nonzero_fmt {
( #[$stability: meta] ( $( $Trait: ident ),+ ) for $Ty: ident ) => {
$(
@ -993,26 +1002,27 @@ $EndFeature, "
```"),
#[stable(feature = "no_panic_pow", since = "1.34.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub fn checked_pow(self, mut exp: u32) -> Option<Self> {
pub const fn checked_pow(self, mut exp: u32) -> Option<Self> {
let mut base = self;
let mut acc: Self = 1;
while exp > 1 {
if (exp & 1) == 1 {
acc = acc.checked_mul(base)?;
acc = try_opt!(acc.checked_mul(base));
}
exp /= 2;
base = base.checked_mul(base)?;
base = try_opt!(base.checked_mul(base));
}
// Deal with the final bit of the exponent separately, since
// squaring the base afterwards is not necessary and may cause a
// needless overflow.
if exp == 1 {
acc = acc.checked_mul(base)?;
acc = try_opt!(acc.checked_mul(base));
}
Some(acc)
@ -1180,10 +1190,11 @@ assert_eq!(", stringify!($SelfT), "::MIN.saturating_pow(3), ", stringify!($SelfT
$EndFeature, "
```"),
#[stable(feature = "no_panic_pow", since = "1.34.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub fn saturating_pow(self, exp: u32) -> Self {
pub const fn saturating_pow(self, exp: u32) -> Self {
match self.checked_pow(exp) {
Some(x) => x,
None if self < 0 && exp % 2 == 1 => Self::min_value(),
@ -1523,10 +1534,11 @@ assert_eq!(3i8.wrapping_pow(6), -39);",
$EndFeature, "
```"),
#[stable(feature = "no_panic_pow", since = "1.34.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub fn wrapping_pow(self, mut exp: u32) -> Self {
pub const fn wrapping_pow(self, mut exp: u32) -> Self {
let mut base = self;
let mut acc: Self = 1;
@ -1900,10 +1912,11 @@ assert_eq!(3i8.overflowing_pow(5), (-13, true));",
$EndFeature, "
```"),
#[stable(feature = "no_panic_pow", since = "1.34.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub fn overflowing_pow(self, mut exp: u32) -> (Self, bool) {
pub const fn overflowing_pow(self, mut exp: u32) -> (Self, bool) {
let mut base = self;
let mut acc: Self = 1;
let mut overflown = false;
@ -1949,11 +1962,12 @@ assert_eq!(x.pow(5), 32);",
$EndFeature, "
```"),
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
#[rustc_inherit_overflow_checks]
pub fn pow(self, mut exp: u32) -> Self {
pub const fn pow(self, mut exp: u32) -> Self {
let mut base = self;
let mut acc = 1;
@ -3119,26 +3133,27 @@ Basic usage:
assert_eq!(", stringify!($SelfT), "::max_value().checked_pow(2), None);", $EndFeature, "
```"),
#[stable(feature = "no_panic_pow", since = "1.34.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub fn checked_pow(self, mut exp: u32) -> Option<Self> {
pub const fn checked_pow(self, mut exp: u32) -> Option<Self> {
let mut base = self;
let mut acc: Self = 1;
while exp > 1 {
if (exp & 1) == 1 {
acc = acc.checked_mul(base)?;
acc = try_opt!(acc.checked_mul(base));
}
exp /= 2;
base = base.checked_mul(base)?;
base = try_opt!(base.checked_mul(base));
}
// Deal with the final bit of the exponent separately, since
// squaring the base afterwards is not necessary and may cause a
// needless overflow.
if exp == 1 {
acc = acc.checked_mul(base)?;
acc = try_opt!(acc.checked_mul(base));
}
Some(acc)
@ -3234,10 +3249,11 @@ assert_eq!(", stringify!($SelfT), "::MAX.saturating_pow(2), ", stringify!($SelfT
$EndFeature, "
```"),
#[stable(feature = "no_panic_pow", since = "1.34.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub fn saturating_pow(self, exp: u32) -> Self {
pub const fn saturating_pow(self, exp: u32) -> Self {
match self.checked_pow(exp) {
Some(x) => x,
None => Self::max_value(),
@ -3527,10 +3543,11 @@ Basic usage:
assert_eq!(3u8.wrapping_pow(6), 217);", $EndFeature, "
```"),
#[stable(feature = "no_panic_pow", since = "1.34.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub fn wrapping_pow(self, mut exp: u32) -> Self {
pub const fn wrapping_pow(self, mut exp: u32) -> Self {
let mut base = self;
let mut acc: Self = 1;
@ -3853,10 +3870,11 @@ Basic usage:
assert_eq!(3u8.overflowing_pow(6), (217, true));", $EndFeature, "
```"),
#[stable(feature = "no_panic_pow", since = "1.34.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub fn overflowing_pow(self, mut exp: u32) -> (Self, bool) {
pub const fn overflowing_pow(self, mut exp: u32) -> (Self, bool) {
let mut base = self;
let mut acc: Self = 1;
let mut overflown = false;
@ -3899,11 +3917,12 @@ Basic usage:
", $Feature, "assert_eq!(2", stringify!($SelfT), ".pow(5), 32);", $EndFeature, "
```"),
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
#[rustc_inherit_overflow_checks]
pub fn pow(self, mut exp: u32) -> Self {
pub const fn pow(self, mut exp: u32) -> Self {
let mut base = self;
let mut acc = 1;
@ -4014,7 +4033,8 @@ assert!(!10", stringify!($SelfT), ".is_power_of_two());", $EndFeature, "
// overflow cases it instead ends up returning the maximum value
// of the type, and can return 0 for 0.
#[inline]
fn one_less_than_next_power_of_two(self) -> Self {
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
const fn one_less_than_next_power_of_two(self) -> Self {
if self <= 1 { return 0; }
let p = self - 1;
@ -4042,10 +4062,11 @@ Basic usage:
assert_eq!(3", stringify!($SelfT), ".next_power_of_two(), 4);", $EndFeature, "
```"),
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
#[inline]
pub fn next_power_of_two(self) -> Self {
// Call the trait to get overflow checks
ops::Add::add(self.one_less_than_next_power_of_two(), 1)
#[rustc_inherit_overflow_checks]
pub const fn next_power_of_two(self) -> Self {
self.one_less_than_next_power_of_two() + 1
}
}
@ -4067,7 +4088,8 @@ $EndFeature, "
```"),
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn checked_next_power_of_two(self) -> Option<Self> {
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
pub const fn checked_next_power_of_two(self) -> Option<Self> {
self.one_less_than_next_power_of_two().checked_add(1)
}
}
@ -4091,7 +4113,8 @@ $EndFeature, "
```"),
#[unstable(feature = "wrapping_next_power_of_two", issue = "32463",
reason = "needs decision on wrapping behaviour")]
pub fn wrapping_next_power_of_two(self) -> Self {
#[rustc_const_unstable(feature = "const_int_pow", issue = "53718")]
pub const fn wrapping_next_power_of_two(self) -> Self {
self.one_less_than_next_power_of_two().wrapping_add(1)
}
}

37
src/test/ui/consts/const-int-pow-rpass.rs
View File

@ -1,11 +1,48 @@
// run-pass
#![feature(const_int_pow)]
#![feature(wrapping_next_power_of_two)]
const IS_POWER_OF_TWO_A: bool = 0u32.is_power_of_two();
const IS_POWER_OF_TWO_B: bool = 32u32.is_power_of_two();
const IS_POWER_OF_TWO_C: bool = 33u32.is_power_of_two();
const POW: u8 = 3u8.pow(5);
const CHECKED_POW_OK: Option<u8> = 3u8.checked_pow(5);
const CHECKED_POW_OVERFLOW: Option<u8> = 3u8.checked_pow(6);
const WRAPPING_POW: u8 = 3u8.wrapping_pow(6);
const OVERFLOWING_POW: (u8, bool) = 3u8.overflowing_pow(6);
const SATURATING_POW: u8 = 3u8.saturating_pow(6);
const NEXT_POWER_OF_TWO: u32 = 3u32.next_power_of_two();
const CHECKED_NEXT_POWER_OF_TWO_OK: Option<u32> = 3u32.checked_next_power_of_two();
const CHECKED_NEXT_POWER_OF_TWO_OVERFLOW: Option<u32> =
u32::max_value().checked_next_power_of_two();
const WRAPPING_NEXT_POWER_OF_TWO: u32 =
u32::max_value().wrapping_next_power_of_two();
fn main() {
assert!(!IS_POWER_OF_TWO_A);
assert!(IS_POWER_OF_TWO_B);
assert!(!IS_POWER_OF_TWO_C);
assert_eq!(POW, 243);
assert_eq!(CHECKED_POW_OK, Some(243));
assert_eq!(CHECKED_POW_OVERFLOW, None);
assert_eq!(WRAPPING_POW, 217);
assert_eq!(OVERFLOWING_POW, (217, true));
assert_eq!(SATURATING_POW, u8::max_value());
assert_eq!(NEXT_POWER_OF_TWO, 4);
assert_eq!(CHECKED_NEXT_POWER_OF_TWO_OK, Some(4));
assert_eq!(CHECKED_NEXT_POWER_OF_TWO_OVERFLOW, None);
assert_eq!(WRAPPING_NEXT_POWER_OF_TWO, 0);
}