Document UniformUsize fields

Author: aleb

src/distr/uniform_int.rs

@@ -413,9 +413,13 @@ uniform_simd_int_impl! { (u8, i8), (u16, i16), (u32, i32), (u64, i64) }
     derive(Deserialize)
 )]
 pub struct UniformUsize {
+    /// The lowest possible value.
     low: usize,
+    /// The number of possible values. `0` has a special meaning: all.
     range: usize,
+    /// Threshold used when sampling to obtain a uniform distribution.
     thresh: usize,
+    /// Whether the largest possible value is greater than `u32::MAX`.
     #[cfg(target_pointer_width = "64")]
     // Handle missing field when deserializing on 64-bit an object serialized
     // on 32-bit. Can be removed when switching to a custom deserializer.
@@ -806,4 +810,57 @@ mod tests {
             );
         }
     }
+
+    #[test]
+    fn test_uniform_usize_empty_range() {
+        assert_eq!(UniformUsize::new(10, 10), Err(Error::EmptyRange));
+        assert!(UniformUsize::new(10, 11).is_ok());
+
+        assert_eq!(UniformUsize::new_inclusive(10, 9), Err(Error::EmptyRange));
+        assert!(UniformUsize::new_inclusive(10, 10).is_ok());
+    }
+
+    #[test]
+    fn test_uniform_usize_constructors() {
+        assert_eq!(
+            UniformUsize::new_inclusive(u32::MAX as usize, u32::MAX as usize),
+            Ok(UniformUsize {
+                low: u32::MAX as usize,
+                range: 1,
+                thresh: 0,
+                #[cfg(target_pointer_width = "64")]
+                mode64: false
+            })
+        );
+        assert_eq!(
+            UniformUsize::new_inclusive(0, u32::MAX as usize),
+            Ok(UniformUsize {
+                low: 0,
+                range: 0,
+                thresh: 0,
+                #[cfg(target_pointer_width = "64")]
+                mode64: false
+            })
+        );
+        #[cfg(target_pointer_width = "64")]
+        assert_eq!(
+            UniformUsize::new_inclusive(0, u32::MAX as usize + 1),
+            Ok(UniformUsize {
+                low: 0,
+                range: u32::MAX as usize + 2,
+                thresh: 1,
+                mode64: true
+            })
+        );
+        #[cfg(target_pointer_width = "64")]
+        assert_eq!(
+            UniformUsize::new_inclusive(u32::MAX as usize, u64::MAX as usize),
+            Ok(UniformUsize {
+                low: u32::MAX as usize,
+                range: u64::MAX as usize - u32::MAX as usize + 1,
+                thresh: u32::MAX as usize,
+                mode64: true
+            })
+        );
+    }
 }