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Add non-panicking variants of pow for integer types #48321

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Feb 28, 2018
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Add non-panicking variants of pow for integer types #48321

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308 changes: 308 additions & 0 deletions src/libcore/num/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -634,6 +634,46 @@ $EndFeature, "
}
}

doc_comment! {
concat!("Checked exponentiation. Computes `self.pow(exp)`, returning `None` if
overflow occurred.

# Examples

Basic usage:

```
#![feature(no_panic_pow)]
", $Feature, "assert_eq!(8", stringify!($SelfT), ".checked_pow(2), Some(64));
assert_eq!(", stringify!($SelfT), "::max_value().checked_pow(2), None);",
$EndFeature, "
```"),

#[unstable(feature = "no_panic_pow", issue = "48320")]
#[inline]
pub 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)?;
}
exp /= 2;
base = 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)?;
}

Some(acc)
}
}

doc_comment! {
concat!("Saturating integer addition. Computes `self + rhs`, saturating at the numeric
bounds instead of overflowing.
Expand Down Expand Up @@ -713,6 +753,34 @@ $EndFeature, "
}
}

doc_comment! {
concat!("Saturating integer exponentiation. Computes `self.pow(exp)`,
saturating at the numeric bounds instead of overflowing.

# Examples

Basic usage:

```
#![feature(no_panic_pow)]
", $Feature, "use std::", stringify!($SelfT), ";

assert_eq!((-4", stringify!($SelfT), ").saturating_pow(3), -64);
assert_eq!(", stringify!($SelfT), "::MIN.saturating_pow(2), ", stringify!($SelfT), "::MAX);
assert_eq!(", stringify!($SelfT), "::MIN.saturating_pow(3), ", stringify!($SelfT), "::MIN);",
$EndFeature, "
```"),
#[unstable(feature = "no_panic_pow", issue = "48320")]
#[inline]
pub 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(),
None => Self::max_value(),
}
}
}

doc_comment! {
concat!("Wrapping (modular) addition. Computes `self + rhs`, wrapping around at the
boundary of the type.
Expand Down Expand Up @@ -947,6 +1015,46 @@ $EndFeature, "
}
}

doc_comment! {
concat!("Wrapping (modular) exponentiation. Computes `self.pow(exp)`,
wrapping around at the boundary of the type.

# Examples

Basic usage:

```
#![feature(no_panic_pow)]
", $Feature, "assert_eq!(3", stringify!($SelfT), ".wrapping_pow(4), 81);
assert_eq!(3i8.wrapping_pow(5), -13);
assert_eq!(3i8.wrapping_pow(6), -39);",
$EndFeature, "
```"),
#[unstable(feature = "no_panic_pow", issue = "48320")]
#[inline]
pub fn wrapping_pow(self, mut exp: u32) -> Self {
let mut base = self;
let mut acc: Self = 1;

while exp > 1 {
if (exp & 1) == 1 {
acc = acc.wrapping_mul(base);
}
exp /= 2;
base = base.wrapping_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.wrapping_mul(base);
}

acc
}
}

doc_comment! {
concat!("Calculates `self` + `rhs`

Expand Down Expand Up @@ -1202,6 +1310,56 @@ $EndFeature, "
doc_comment! {
concat!("Raises self to the power of `exp`, using exponentiation by squaring.

Returns a tuple of the exponentiation along with a bool indicating
whether an overflow happened.

# Examples

Basic usage:

```
#![feature(no_panic_pow)]
", $Feature, "assert_eq!(3", stringify!($SelfT), ".overflowing_pow(4), (81, false));
assert_eq!(3i8.overflowing_pow(5), (-13, true));",
$EndFeature, "
```"),
#[unstable(feature = "no_panic_pow", issue = "48320")]
#[inline]
pub fn overflowing_pow(self, mut exp: u32) -> (Self, bool) {
let mut base = self;
let mut acc: Self = 1;
let mut overflown = false;
// Scratch space for storing results of overflowing_mul.
let mut r;

while exp > 1 {
if (exp & 1) == 1 {
r = acc.overflowing_mul(base);
acc = r.0;
overflown |= r.1;
}
exp /= 2;
r = base.overflowing_mul(base);
base = r.0;
overflown |= r.1;
}

// 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 {
r = acc.overflowing_mul(base);
acc = r.0;
overflown |= r.1;
}

(acc, overflown)
}
}

doc_comment! {
concat!("Raises self to the power of `exp`, using exponentiation by squaring.

# Examples

Basic usage:
Expand Down Expand Up @@ -1887,6 +2045,44 @@ assert_eq!(0x10", stringify!($SelfT), ".checked_shr(129), None);", $EndFeature,
}
}

doc_comment! {
concat!("Checked exponentiation. Computes `self.pow(exp)`, returning `None` if
overflow occurred.

# Examples

Basic usage:

```
#![feature(no_panic_pow)]
", $Feature, "assert_eq!(2", stringify!($SelfT), ".checked_pow(5), Some(32));
assert_eq!(", stringify!($SelfT), "::max_value().checked_pow(2), None);", $EndFeature, "
```"),
#[unstable(feature = "no_panic_pow", issue = "48320")]
#[inline]
pub 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)?;
}
exp /= 2;
base = 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)?;
}

Some(acc)
}
}

doc_comment! {
concat!("Saturating integer addition. Computes `self + rhs`, saturating at
the numeric bounds instead of overflowing.
Expand Down Expand Up @@ -1953,6 +2149,32 @@ assert_eq!((", stringify!($SelfT), "::MAX).saturating_mul(10), ", stringify!($Se
}
}

doc_comment! {
concat!("Saturating integer exponentiation. Computes `self.pow(exp)`,
saturating at the numeric bounds instead of overflowing.

# Examples

Basic usage:

```
#![feature(no_panic_pow)]
", $Feature, "use std::", stringify!($SelfT), ";

assert_eq!(4", stringify!($SelfT), ".saturating_pow(3), 64);
assert_eq!(", stringify!($SelfT), "::MAX.saturating_pow(2), ", stringify!($SelfT), "::MAX);",
$EndFeature, "
```"),
#[unstable(feature = "no_panic_pow", issue = "48320")]
#[inline]
pub fn saturating_pow(self, exp: u32) -> Self {
match self.checked_pow(exp) {
Some(x) => x,
None => Self::max_value(),
}
}
}

doc_comment! {
concat!("Wrapping (modular) addition. Computes `self + rhs`,
wrapping around at the boundary of the type.
Expand Down Expand Up @@ -2147,6 +2369,44 @@ assert_eq!(128", stringify!($SelfT), ".wrapping_shr(128), 128);", $EndFeature, "
}
}

doc_comment! {
concat!("Wrapping (modular) exponentiation. Computes `self.pow(exp)`,
wrapping around at the boundary of the type.

# Examples

Basic usage:

```
#![feature(no_panic_pow)]
", $Feature, "assert_eq!(3", stringify!($SelfT), ".wrapping_pow(5), 243);
assert_eq!(3u8.wrapping_pow(6), 217);", $EndFeature, "
```"),
#[unstable(feature = "no_panic_pow", issue = "48320")]
#[inline]
pub fn wrapping_pow(self, mut exp: u32) -> Self {
let mut base = self;
let mut acc: Self = 1;

while exp > 1 {
if (exp & 1) == 1 {
acc = acc.wrapping_mul(base);
}
exp /= 2;
base = base.wrapping_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.wrapping_mul(base);
}

acc
}
}

doc_comment! {
concat!("Calculates `self` + `rhs`

Expand Down Expand Up @@ -2353,7 +2613,55 @@ assert_eq!(0x10", stringify!($SelfT), ".overflowing_shr(132), (0x1, true));", $E
pub fn overflowing_shr(self, rhs: u32) -> (Self, bool) {
(self.wrapping_shr(rhs), (rhs > ($BITS - 1)))
}
}

doc_comment! {
concat!("Raises self to the power of `exp`, using exponentiation by squaring.

Returns a tuple of the exponentiation along with a bool indicating
whether an overflow happened.

# Examples

Basic usage:

```
#![feature(no_panic_pow)]
", $Feature, "assert_eq!(3", stringify!($SelfT), ".overflowing_pow(5), (243, false));
assert_eq!(3u8.overflowing_pow(6), (217, true));", $EndFeature, "
```"),
#[unstable(feature = "no_panic_pow", issue = "48320")]
#[inline]
pub fn overflowing_pow(self, mut exp: u32) -> (Self, bool) {
let mut base = self;
let mut acc: Self = 1;
let mut overflown = false;
// Scratch space for storing results of overflowing_mul.
let mut r;

while exp > 1 {
if (exp & 1) == 1 {
r = acc.overflowing_mul(base);
acc = r.0;
overflown |= r.1;
}
exp /= 2;
r = base.overflowing_mul(base);
base = r.0;
overflown |= r.1;
}

// 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 {
r = acc.overflowing_mul(base);
acc = r.0;
overflown |= r.1;
}

(acc, overflown)
}
}

doc_comment! {
Expand Down