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// -*- mode: rust; -*-
//
// This file is part of curve25519-dalek.
// Copyright (c) 2016-2017 Isis Lovecruft, Henry de Valence
// See LICENSE for licensing information.
//
// Authors:
// - Isis Agora Lovecruft <isis@patternsinthevoid.net>
// - Henry de Valence <hdevalence@hdevalence.ca>

//! Module for common traits.

use subtle;

// ------------------------------------------------------------------------
// Public Traits
// ------------------------------------------------------------------------

/// Trait for getting the identity element of a point type.
pub trait Identity {
    /// Returns the identity element of the curve.
    /// Can be used as a constructor.
    fn identity() -> Self;
}

/// Trait for testing if a curve point is equivalent to the identity point.
pub trait IsIdentity {
    /// Return true if this element is the identity element of the curve.
    fn is_identity(&self) -> bool;
}

/// Implement generic identity equality testing for a point representations
/// which have constant-time equality testing and a defined identity
/// constructor.
impl<T> IsIdentity for T where T: subtle::ConstantTimeEq + Identity {
    fn is_identity(&self) -> bool {
        self.ct_eq(&T::identity()).unwrap_u8() == 1u8
    }
}

// ------------------------------------------------------------------------
// Private Traits
// ------------------------------------------------------------------------

/// Trait for checking whether a point is on the curve.
///
/// This trait is only for debugging/testing, since it should be
/// impossible for a `curve25519-dalek` user to construct an invalid
/// point.
pub(crate) trait ValidityCheck {
    /// Checks whether the point is on the curve. Not CT.
    fn is_valid(&self) -> bool;
}