Add p() for Bernoulli (#1481)

Co-authored-by: Diggory Hardy <git@dhardy.name>

CHANGELOG.md

@@ -21,6 +21,7 @@ You may also find the [Upgrade Guide](https://rust-random.github.io/book/update.
 - Rename `rand::distributions` to `rand::distr` (#1470)
 - The `serde1` feature has been renamed `serde` (#1477)
 - Mark `WeightError`, `PoissonError`, `BinomialError` as `#[non_exhaustive]` (#1480).
+- Add `p()` for `Bernoulli` to access probability (#1481)
 - Add `UniformUsize` and use to make `Uniform` for `usize` portable (#1487)
 - Remove support for generating `isize` and `usize` values with `Standard`, `Uniform` and `Fill` and usage as a `WeightedAliasIndex` weight (#1487)
 - Require `Clone` and `AsRef` bound for `SeedableRng::Seed`. (#1491)

src/distr/bernoulli.rs

@@ -136,6 +136,18 @@ impl Bernoulli {
         let p_int = ((f64::from(numerator) / f64::from(denominator)) * SCALE) as u64;
         Ok(Bernoulli { p_int })
     }
+
+    #[inline]
+    /// Returns the probability (`p`) of the distribution.
+    ///
+    /// This value may differ slightly from the input due to loss of precision.
+    pub fn p(&self) -> f64 {
+        if self.p_int == ALWAYS_TRUE {
+            1.0
+        } else {
+            (self.p_int as f64) / SCALE
+        }
+    }
 }
 
 impl Distribution<bool> for Bernoulli {