Additional Canon64 variants

Author: dhardy

benches/uniform.rs

@@ -61,6 +61,7 @@ macro_rules! bench_int {
         bench_dist_int_group!("Old", $T, sample, g, inputs);
         bench_dist_int_group!("Lemire", $T, sample_lemire, g, inputs);
         bench_dist_int_group!("Canon", $T, sample_canon, g, inputs);
+        bench_dist_int_group!("Canon64", $T, sample_canon_64, g, inputs);
         bench_dist_int_group!("Canon-Lemire", $T, sample_canon_lemire, g, inputs);
         bench_dist_int_group!("Bitmask", $T, sample_bitmask, g, inputs);
         drop(g);
@@ -82,10 +83,6 @@ fn uniform_int(c: &mut Criterion) {
     bench_int!(c, i32, (i32::MIN, 1));
     bench_int!(c, i64, (i64::MIN, 1));
     bench_int!(c, i128, (i128::MIN, 1));
-
-    let inputs = &[("high_reject", (i128::MIN, 1)), ("low_reject", (-1, 2))];
-    let mut g = c.benchmark_group(concat!("uniform_dist_int_", stringify!(i128)));
-    bench_dist_int_group!("Canon64", i128, sample_canon_64, g, inputs);
 }
 
 #[cfg(feature = "simd_support")]

src/distributions/uniform/uniform_int.rs

@@ -461,11 +461,46 @@ mod isize_int_impls {
     uniform_int_impl! { usize, usize, usize, usize }
 }
 
+macro_rules! uniform_int_64_impl {
+    ($ty:ty, $unsigned:ident) => {
+        impl UniformInt<$ty> {
+            /// Sample, Canon's method variant
+            #[inline]
+            pub fn sample_canon_64<R: Rng + ?Sized>(&self, rng: &mut R) -> $ty {
+                let range = self.range as $unsigned as u64;
+                if range == 0 {
+                    return rng.gen();
+                }
+
+                let (result, _lo1) = rng.gen::<u64>().wmul(range);
+                // bias is at most 1 in 2.pow(56) for i8, 1 in 2.pow(48) for i16
+                self.low.wrapping_add(result as $ty)
+            }
+        }
+    }
+}
+uniform_int_64_impl!(i8, u8);
+uniform_int_64_impl!(i16, u16);
+
+macro_rules! uniform_int_64void_impl {
+    ($ty:ty) => {
+        impl UniformInt<$ty> {
+            /// Sample, Canon's method variant
+            #[inline]
+            pub fn sample_canon_64<R: Rng + ?Sized>(&self, _rng: &mut R) -> $ty {
+                Default::default() // not used
+            }
+        }
+    }
+}
+uniform_int_64void_impl!(i32);
+uniform_int_64void_impl!(i64);
+
 impl UniformInt<i128> {
     /// Sample, Canon's method variant
     #[inline]
     pub fn sample_canon_64<R: Rng + ?Sized>(&self, rng: &mut R) -> i128 {
-        let range = self.range as i128 as u128;
+        let range = self.range as u128;
         if range == 0 {
             return rng.gen();
         }