Trait ConditionallySelectable 

pub trait ConditionallySelectable: Copy {
    // Required method
    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self;

    // Provided methods
    fn conditional_assign(&mut self, other: &Self, choice: Choice) { ... }
    fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice) { ... }
}

A type which can be conditionally selected in constant time.

This trait also provides generic implementations of conditional assignment and conditional swaps.

Required Methods

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

Select a or b according to choice.

Returns

• a if choice == Choice(0);
• b if choice == Choice(1).

This function should execute in constant time.

Example

use subtle::ConditionallySelectable;
let x: u8 = 13;
let y: u8 = 42;

let z = u8::conditional_select(&x, &y, 0.into());
assert_eq!(z, x);
let z = u8::conditional_select(&x, &y, 1.into());
assert_eq!(z, y);

Provided Methods

fn conditional_assign(&mut self, other: &Self, choice: Choice)

Conditionally assign other to self, according to choice.

This function should execute in constant time.

Example

use subtle::ConditionallySelectable;
let mut x: u8 = 13;
let mut y: u8 = 42;

x.conditional_assign(&y, 0.into());
assert_eq!(x, 13);
x.conditional_assign(&y, 1.into());
assert_eq!(x, 42);

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

Conditionally swap self and other if choice == 1; otherwise, reassign both unto themselves.

This function should execute in constant time.

Example

use subtle::ConditionallySelectable;
let mut x: u8 = 13;
let mut y: u8 = 42;

u8::conditional_swap(&mut x, &mut y, 0.into());
assert_eq!(x, 13);
assert_eq!(y, 42);
u8::conditional_swap(&mut x, &mut y, 1.into());
assert_eq!(x, 42);
assert_eq!(y, 13);

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 ConditionallySelectable for Ordering

Ordering is #[repr(i8)] where:

• Less => -1
• Equal => 0
• Greater => 1

Given this, it’s possible to operate on orderings as if they’re integers, which allows leveraging conditional masking for predication.

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

impl ConditionallySelectable for i8

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

impl ConditionallySelectable for i16

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

impl ConditionallySelectable for i32

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

impl ConditionallySelectable for i64

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

impl ConditionallySelectable for i128

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

impl ConditionallySelectable for u8

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

impl ConditionallySelectable for u16

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

impl ConditionallySelectable for u32

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

impl ConditionallySelectable for u64

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

impl ConditionallySelectable for u128

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)

impl<T, const N: usize> ConditionallySelectable for [T; N]

where T: ConditionallySelectable,

Available on crate feature const-generics only.

fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self

fn conditional_assign(&mut self, other: &Self, choice: Choice)

Implementors

impl ConditionallySelectable for Choice

impl<T: ConditionallySelectable> ConditionallySelectable for CtOption<T>