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diff --git a/rand/rand_distr/src/unit_sphere.rs b/rand/rand_distr/src/unit_sphere.rs
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+++ b/rand/rand_distr/src/unit_sphere.rs
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+// Copyright 2018-2019 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use rand::Rng;
+use crate::{Distribution, Uniform, uniform::SampleUniform};
+use crate::utils::Float;
+
+/// Samples uniformly from the surface of the unit sphere in three dimensions.
+///
+/// Implemented via a method by Marsaglia[^1].
+///
+///
+/// # Example
+///
+/// ```
+/// use rand_distr::{UnitSphere, Distribution};
+///
+/// let v: [f64; 3] = UnitSphere.sample(&mut rand::thread_rng());
+/// println!("{:?} is from the unit sphere surface.", v)
+/// ```
+///
+/// [^1]: Marsaglia, George (1972). [*Choosing a Point from the Surface of a
+///       Sphere.*](https://doi.org/10.1214/aoms/1177692644)
+///       Ann. Math. Statist. 43, no. 2, 645--646.
+#[derive(Clone, Copy, Debug)]
+pub struct UnitSphere;
+
+impl<N: Float + SampleUniform> Distribution<[N; 3]> for UnitSphere {
+    #[inline]
+    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> [N; 3] {
+        let uniform = Uniform::new(N::from(-1.), N::from(1.));
+        loop {
+            let (x1, x2) = (uniform.sample(rng), uniform.sample(rng));
+            let sum = x1*x1 + x2*x2;
+            if sum >= N::from(1.) {
+                continue;
+            }
+            let factor = N::from(2.) * (N::from(1.0) - sum).sqrt();
+            return [x1 * factor, x2 * factor, N::from(1.) - N::from(2.)*sum];
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::Distribution;
+    use super::UnitSphere;
+
+    /// Assert that two numbers are almost equal to each other.
+    ///
+    /// On panic, this macro will print the values of the expressions with their
+    /// debug representations.
+    macro_rules! assert_almost_eq {
+        ($a:expr, $b:expr, $prec:expr) => (
+            let diff = ($a - $b).abs();
+            if diff > $prec {
+                panic!(format!(
+                    "assertion failed: `abs(left - right) = {:.1e} < {:e}`, \
+                     (left: `{}`, right: `{}`)",
+                    diff, $prec, $a, $b));
+            }
+        );
+    }
+
+    #[test]
+    fn norm() {
+        let mut rng = crate::test::rng(1);
+        for _ in 0..1000 {
+            let x: [f64; 3] = UnitSphere.sample(&mut rng);
+            assert_almost_eq!(x[0]*x[0] + x[1]*x[1] + x[2]*x[2], 1., 1e-15);
+        }
+    }
+
+    #[test]
+    fn value_stability() {
+        let mut rng = crate::test::rng(2);
+        let expected = [
+                [0.03247542860231647, -0.7830477442152738, 0.6211131755296027],
+                [-0.09978440840914075, 0.9706650829833128, -0.21875184231323952],
+                [0.2735582468624679, 0.9435374242279655, -0.1868234852870203],
+            ];
+        let samples: [[f64; 3]; 3] = [
+                UnitSphere.sample(&mut rng),
+                UnitSphere.sample(&mut rng),
+                UnitSphere.sample(&mut rng),
+            ];
+        assert_eq!(samples, expected);
+    }
+}