1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52

use ark_std::rand::RngCore;
use core::num::NonZeroU32;

/// `OptionalRng` is a hack that is necessary because `Option<&mut R>` is not implicitly reborrowed
/// like `&mut R` is. This causes problems when a variable of type `Option<&mut R>`
/// is moved (eg, in a loop).
///
/// To overcome this, we define the wrapper `OptionalRng` here that can be borrowed
/// mutably, without fear of being moved.
pub struct OptionalRng<R>(pub Option<R>);

impl<R: RngCore> RngCore for OptionalRng<R> {
    #[inline]
    fn next_u32(&mut self) -> u32 {
        (&mut self.0)
            .as_mut()
            .map(|r| r.next_u32())
            .expect("Rng was invoked in a non-hiding context")
    }

    #[inline]
    fn next_u64(&mut self) -> u64 {
        (&mut self.0)
            .as_mut()
            .map(|r| r.next_u64())
            .expect("Rng was invoked in a non-hiding context")
    }

    #[inline]
    fn fill_bytes(&mut self, dest: &mut [u8]) {
        (&mut self.0)
            .as_mut()
            .map(|r| r.fill_bytes(dest))
            .expect("Rng was invoked in a non-hiding context")
    }

    #[inline]
    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), ark_std::rand::Error> {
        match &mut self.0 {
            Some(r) => r.try_fill_bytes(dest),
            None => Err(NonZeroU32::new(ark_std::rand::Error::CUSTOM_START)
                .unwrap()
                .into()),
        }
    }
}

impl<R: RngCore> From<R> for OptionalRng<R> {
    fn from(other: R) -> Self {
        Self(Some(other))
    }
}