Trait CheckedDoubleFactorial

pub trait CheckedDoubleFactorial: Sized {
    // Required method
    fn checked_double_factorial(n: u64) -> Option<Self>;
}

Computes the double factorial of a u64, returning None if the result is too large to be represented. The double factorial of a non-negative integer is the product of all the positive integers that are less than or equal to it and have the same parity as it.

Required Methods

fn checked_double_factorial(n: u64) -> Option<Self>

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

impl CheckedDoubleFactorial for u8

fn checked_double_factorial(n: u64) -> Option<u8>

Computes the double factorial of a number.

If the input is too large, the function returns None.

$$ f(n) = \begin{cases} \operatorname{Some}(n!!) & \text{if} \quad n!! < 2^W, \\ \operatorname{None} & \text{if} \quad n!! \geq 2^W, \end{cases} $$ where $W$ is Self::WIDTH.

$n!! = O(\sqrt{n}(n/e)^{n/2})$.

Worst-case complexity

Constant time and additional memory.

Examples

See here.

impl CheckedDoubleFactorial for u16

fn checked_double_factorial(n: u64) -> Option<u16>

Computes the double factorial of a number.

If the input is too large, the function returns None.

$$ f(n) = \begin{cases} \operatorname{Some}(n!!) & \text{if} \quad n!! < 2^W, \\ \operatorname{None} & \text{if} \quad n!! \geq 2^W, \end{cases} $$ where $W$ is Self::WIDTH.

$n!! = O(\sqrt{n}(n/e)^{n/2})$.

Worst-case complexity

Constant time and additional memory.

Examples

See here.

impl CheckedDoubleFactorial for u32

fn checked_double_factorial(n: u64) -> Option<u32>

Computes the double factorial of a number.

If the input is too large, the function returns None.

$$ f(n) = \begin{cases} \operatorname{Some}(n!!) & \text{if} \quad n!! < 2^W, \\ \operatorname{None} & \text{if} \quad n!! \geq 2^W, \end{cases} $$ where $W$ is Self::WIDTH.

$n!! = O(\sqrt{n}(n/e)^{n/2})$.

Worst-case complexity

Constant time and additional memory.

Examples

See here.

impl CheckedDoubleFactorial for u64

fn checked_double_factorial(n: u64) -> Option<u64>

Computes the double factorial of a number.

If the input is too large, the function returns None.

$$ f(n) = \begin{cases} \operatorname{Some}(n!!) & \text{if} \quad n!! < 2^W, \\ \operatorname{None} & \text{if} \quad n!! \geq 2^W, \end{cases} $$ where $W$ is Self::WIDTH.

$n!! = O(\sqrt{n}(n/e)^{n/2})$.

Worst-case complexity

Constant time and additional memory.

Examples

See here.

impl CheckedDoubleFactorial for u128

fn checked_double_factorial(n: u64) -> Option<u128>

Computes the double factorial of a number.

If the input is too large, the function returns None.

$$ f(n) = \begin{cases} \operatorname{Some}(n!!) & \text{if} \quad n!! < 2^W, \\ \operatorname{None} & \text{if} \quad n!! \geq 2^W, \end{cases} $$ where $W$ is Self::WIDTH.

$n!! = O(\sqrt{n}(n/e)^{n/2})$.

Worst-case complexity

Constant time and additional memory.

Examples

See here.

impl CheckedDoubleFactorial for usize

fn checked_double_factorial(n: u64) -> Option<usize>

Computes the double factorial of a usize.

If the input is too large, the function returns None.

$$ f(n) = \begin{cases} \operatorname{Some}(n!!) & \text{if} \quad n!! < 2^W, \\ \operatorname{None} & \text{if} \quad n!! \geq 2^W, \end{cases} $$ where $W$ is usize::WIDTH.

$n!! = O(\sqrt{n}(n/e)^{n/2})$.

Worst-case complexity

Constant time and additional memory.

Examples

See here.

Implementors