Merge pull request #1087 from GautierMinster/fix_uniform_int_panic_on_full_inclusive_range

distributions/uniform: fix panic in gen_range(0..=MAX)

Author: dhardy

CHANGELOG.md

@@ -8,6 +8,11 @@ A [separate changelog is kept for rand_core](rand_core/CHANGELOG.md).
 
 You may also find the [Upgrade Guide](https://rust-random.github.io/book/update.html) useful.
 
+## [0.8.2] - 2021-01-12
+### Fixes
+- Fix panic in `UniformInt::sample_single_inclusive` and `Rng::gen_range` when
+  providing a full integer range (eg `0..=MAX`) (#1087)
+
 ## [0.8.1] - 2020-12-31
 ### Other
 - Enable all stable features in the playground (#1081)

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "rand"
-version = "0.8.1"
+version = "0.8.2"
 authors = ["The Rand Project Developers", "The Rust Project Developers"]
 license = "MIT OR Apache-2.0"
 readme = "README.md"

src/distributions/uniform.rs

@@ -521,6 +521,12 @@ macro_rules! uniform_int_impl {
                 let high = *high_b.borrow();
                 assert!(low <= high, "UniformSampler::sample_single_inclusive: low > high");
                 let range = high.wrapping_sub(low).wrapping_add(1) as $unsigned as $u_large;
+                // If the above resulted in wrap-around to 0, the range is $ty::MIN..=$ty::MAX,
+                // and any integer will do.
+                if range == 0 {
+                    return rng.gen();
+                }
+
                 let zone = if ::core::$unsigned::MAX <= ::core::u16::MAX as $unsigned {
                     // Using a modulus is faster than the approximation for
                     // i8 and i16. I suppose we trade the cost of one
@@ -1235,6 +1241,11 @@ mod tests {
                         let v = <$ty as SampleUniform>::Sampler::sample_single(low, high, &mut rng);
                         assert!($le(low, v) && $lt(v, high));
                     }
+
+                    for _ in 0..1000 {
+                        let v = <$ty as SampleUniform>::Sampler::sample_single_inclusive(low, high, &mut rng);
+                        assert!($le(low, v) && $le(v, high));
+                    }
                 }
             }};