Use black_box to prevent constant propagation

benches/reject.rs

@@ -4,7 +4,7 @@ extern crate test;
 
 use rand::prelude::*;
 use rand::distributions::uniform::{UniformInt, UniformSampler};
-use test::Bencher;
+use test::{Bencher, black_box};
 
 // In src/distributions/uniform.rs, we say:
 // Implementation of [`sample_single`] is optional, and is only useful when
@@ -22,10 +22,10 @@ macro_rules! sample_dist {
         #[bench]
         fn $fnn(b: &mut Bencher) {
             let mut rng = thread_rng();
-            let dist = UniformInt::<u32>::new($low, $high);
+            let dist = UniformInt::<u32>::new(black_box($low), black_box($high));
             b.iter(|| {
-                test::black_box(dist.sample(&mut rng));
-                test::black_box(dist.sample(&mut rng));
+                black_box(dist.sample(&mut rng));
+                black_box(dist.sample(&mut rng));
             });
         }
     };
@@ -38,8 +38,8 @@ macro_rules! sample_single {
         fn $fnn(b: &mut Bencher) {
             let mut rng = thread_rng();
             b.iter(|| {
-                test::black_box(UniformInt::<u32>::sample_single($low, $high, &mut rng));
-                test::black_box(UniformInt::<u32>::sample_single($low, $high, &mut rng));
+                black_box(UniformInt::<u32>::sample_single(black_box($low), black_box($high), &mut rng));
+                black_box(UniformInt::<u32>::sample_single(black_box($low), black_box($high), &mut rng));
             });
         }
     };
@@ -51,7 +51,7 @@ macro_rules! sample_single {
 // n/2+1: almost half of the values are rejected, and we can do no better
 // n/2: half the values are rejected, but could be doubled to have no rejection
 // n/2-1: only a few values are rejected: expect this to be fast
-// 4: almost half that values are rejected, but could have no rejection
+// 4: half the values are rejected, but could have no rejection
 // 3: 25% rejected, but we could reject one value
 
 const HALF_32_BIT_UNSIGNED: u32 = 1 << 31;