use super::Limb;
use crate::{Encoding, NonZero, Random, RandomMod};
use rand_core::CryptoRngCore;
use subtle::ConstantTimeLess;
impl Random for Limb {
#[cfg(target_pointer_width = "32")]
fn random(rng: &mut impl CryptoRngCore) -> Self {
Self(rng.next_u32())
}
#[cfg(target_pointer_width = "64")]
fn random(rng: &mut impl CryptoRngCore) -> Self {
Self(rng.next_u64())
}
}
impl RandomMod for Limb {
fn random_mod(rng: &mut impl CryptoRngCore, modulus: &NonZero<Self>) -> Self {
let mut bytes = <Self as Encoding>::Repr::default();
let n_bits = modulus.bits();
let n_bytes = (n_bits + 7) / 8;
let mask = 0xff >> (8 * n_bytes - n_bits);
loop {
rng.fill_bytes(&mut bytes[..n_bytes]);
bytes[n_bytes - 1] &= mask;
let n = Limb::from_le_bytes(bytes);
if n.ct_lt(modulus).into() {
return n;
}
}
}
}