Let gen_range support ..len and ..=len for unsigned ints

Author: dhardy

src/distr/uniform.rs

@@ -120,7 +120,7 @@ mod other;
 pub use other::{UniformChar, UniformDuration};
 
 use core::fmt;
-use core::ops::{Range, RangeInclusive};
+use core::ops::{Range, RangeInclusive, RangeTo, RangeToInclusive};
 
 use crate::distr::Distribution;
 use crate::{Rng, RngCore};
@@ -439,6 +439,41 @@ impl<T: SampleUniform + PartialOrd> SampleRange<T> for RangeInclusive<T> {
     }
 }
 
+macro_rules! impl_sample_range_u {
+    ($t:ty) => {
+        impl SampleRange<$t> for RangeTo<$t> {
+            #[inline]
+            fn sample_single<R: RngCore + ?Sized>(self, rng: &mut R) -> Result<$t, Error> {
+                <$t as SampleUniform>::Sampler::sample_single(0, self.end, rng)
+            }
+
+            #[inline]
+            fn is_empty(&self) -> bool {
+                0 == self.end
+            }
+        }
+
+        impl SampleRange<$t> for RangeToInclusive<$t> {
+            #[inline]
+            fn sample_single<R: RngCore + ?Sized>(self, rng: &mut R) -> Result<$t, Error> {
+                <$t as SampleUniform>::Sampler::sample_single_inclusive(0, self.end, rng)
+            }
+
+            #[inline]
+            fn is_empty(&self) -> bool {
+                false
+            }
+        }
+    };
+}
+
+impl_sample_range_u!(u8);
+impl_sample_range_u!(u16);
+impl_sample_range_u!(u32);
+impl_sample_range_u!(u64);
+impl_sample_range_u!(u128);
+impl_sample_range_u!(usize);
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/rng.rs

@@ -102,7 +102,8 @@ pub trait Rng: RngCore {
     /// made from the given range. See also the [`Uniform`] distribution
     /// type which may be faster if sampling from the same range repeatedly.
     ///
-    /// Only `gen_range(low..high)` and `gen_range(low..=high)` are supported.
+    /// All types support `low..high_exclusive` and `low..=high` range syntax.
+    /// Unsigned integer types also support `..high_exclusive` and `..=high` syntax.
     ///
     /// # Panics
     ///
@@ -116,13 +117,13 @@ pub trait Rng: RngCore {
     /// let mut rng = thread_rng();
     ///
     /// // Exclusive range
-    /// let n: u32 = rng.gen_range(0..10);
+    /// let n: u32 = rng.gen_range(..10);
     /// println!("{}", n);
     /// let m: f64 = rng.gen_range(-40.0..1.3e5);
     /// println!("{}", m);
     ///
     /// // Inclusive range
-    /// let n: u32 = rng.gen_range(0..=10);
+    /// let n: u32 = rng.gen_range(..=10);
     /// println!("{}", n);
     /// ```
     ///
@@ -500,7 +501,7 @@ mod test {
             let a: u32 = r.gen_range(12..=24);
             assert!((12..=24).contains(&a));
 
-            assert_eq!(r.gen_range(0u32..1), 0u32);
+            assert_eq!(r.gen_range(..1u32), 0u32);
             assert_eq!(r.gen_range(-12i64..-11), -12i64);
             assert_eq!(r.gen_range(3_000_000..3_000_001), 3_000_000);
         }

src/seq/index.rs

@@ -434,7 +434,7 @@ where
     debug_assert!(amount <= length);
     let mut indices = Vec::with_capacity(amount as usize);
     for j in length - amount..length {
-        let t = rng.gen_range(0..=j);
+        let t = rng.gen_range(..=j);
         if let Some(pos) = indices.iter().position(|&x| x == t) {
             indices[pos] = j;
         }

src/seq/iterator.rs

@@ -70,7 +70,7 @@ pub trait IteratorRandom: Iterator + Sized {
             return match lower {
                 0 => None,
                 1 => self.next(),
-                _ => self.nth(rng.gen_range(0..lower)),
+                _ => self.nth(rng.gen_range(..lower)),
             };
         }
 
@@ -80,7 +80,7 @@ pub trait IteratorRandom: Iterator + Sized {
         // Continue until the iterator is exhausted
         loop {
             if lower > 1 {
-                let ix = coin_flipper.rng.gen_range(0..lower + consumed);
+                let ix = coin_flipper.rng.gen_range(..lower + consumed);
                 let skip = if ix < lower {
                     result = self.nth(ix);
                     lower - (ix + 1)
@@ -203,7 +203,7 @@ pub trait IteratorRandom: Iterator + Sized {
 
         // Continue, since the iterator was not exhausted
         for (i, elem) in self.enumerate() {
-            let k = rng.gen_range(0..i + 1 + amount);
+            let k = rng.gen_range(..i + 1 + amount);
             if let Some(slot) = buf.get_mut(k) {
                 *slot = elem;
             }
@@ -239,7 +239,7 @@ pub trait IteratorRandom: Iterator + Sized {
         // If the iterator stops once, then so do we.
         if reservoir.len() == amount {
             for (i, elem) in self.enumerate() {
-                let k = rng.gen_range(0..i + 1 + amount);
+                let k = rng.gen_range(..i + 1 + amount);
                 if let Some(slot) = reservoir.get_mut(k) {
                     *slot = elem;
                 }

src/seq/mod.rs

@@ -69,7 +69,7 @@ pub mod index {
         // Floyd's algorithm
         let mut indices = [0; N];
         for (i, j) in (len - N..len).enumerate() {
-            let t = rng.gen_range(0..j + 1);
+            let t = rng.gen_range(..j + 1);
             if let Some(pos) = indices[0..i].iter().position(|&x| x == t) {
                 indices[pos] = j;
             }

src/seq/slice.rs

@@ -57,7 +57,7 @@ pub trait IndexedRandom: Index<usize> {
         if self.is_empty() {
             None
         } else {
-            Some(&self[rng.gen_range(0..self.len())])
+            Some(&self[rng.gen_range(..self.len())])
         }
     }
 
@@ -259,7 +259,7 @@ pub trait IndexedMutRandom: IndexedRandom + IndexMut<usize> {
             None
         } else {
             let len = self.len();
-            Some(&mut self[rng.gen_range(0..len)])
+            Some(&mut self[rng.gen_range(..len)])
         }
     }
 
@@ -410,7 +410,7 @@ impl<T> SliceRandom for [T] {
             }
         } else {
             for i in m..self.len() {
-                let index = rng.gen_range(0..i + 1);
+                let index = rng.gen_range(..i + 1);
                 self.swap(i, index);
             }
         }