Struct subtle::Choice

pub struct Choice(_);

The Choice struct represents a choice for use in conditional assignment.

It is a wrapper around a u8, which should have the value either 1 (true) or 0 (false).

The conversion from u8 to Choice passes the value through an optimization barrier, as a best-effort attempt to prevent the compiler from inferring that the Choice value is a boolean. This strategy is based on Tim Maclean's work on rust-timing-shield, which attempts to provide a more comprehensive approach for preventing software side-channels in Rust code.

The Choice struct implements operators for AND, OR, XOR, and NOT, to allow combining Choice values. These operations do not short-circuit.

Implementations

impl Choice

pub fn unwrap_u8(&self) -> u8

Unwrap the Choice wrapper to reveal the underlying u8.

Note

This function only exists as an escape hatch for the rare case where it's not possible to use one of the subtle-provided trait impls.

To convert a Choice to a bool, use the From implementation instead.

Trait Implementations

impl BitAnd<Choice> for Choice

type Output = Choice

The resulting type after applying the & operator.

pub fn bitand(self, rhs: Choice) -> Choice

Performs the & operation.

impl BitAndAssign<Choice> for Choice

pub fn bitand_assign(&mut self, rhs: Choice)

Performs the &= operation.

impl BitOr<Choice> for Choice

type Output = Choice

The resulting type after applying the | operator.

pub fn bitor(self, rhs: Choice) -> Choice

Performs the | operation.

impl BitOrAssign<Choice> for Choice

pub fn bitor_assign(&mut self, rhs: Choice)

Performs the |= operation.

impl BitXor<Choice> for Choice

type Output = Choice

The resulting type after applying the ^ operator.

pub fn bitxor(self, rhs: Choice) -> Choice

Performs the ^ operation.

impl BitXorAssign<Choice> for Choice

pub fn bitxor_assign(&mut self, rhs: Choice)

Performs the ^= operation.

impl Clone for Choice

pub fn clone(&self) -> Choice

Returns a copy of the value.

pub fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl ConditionallySelectable for Choice

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

Select a or b according to choice.

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

Conditionally assign other to self, according to choice.

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

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

impl ConstantTimeEq for Choice

pub fn ct_eq(&self, rhs: &Choice) -> Choice

Determine if two items are equal.

impl Copy for Choice

impl Debug for Choice

pub fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl From<u8> for Choice

pub fn from(input: u8) -> Choice

Performs the conversion.

impl Not for Choice

type Output = Choice

The resulting type after applying the ! operator.

pub fn not(self) -> Choice

Performs the unary ! operation.