Combinations: add benchmarks

Add benchmarks for Combinations iterator of for return Vec sizes of 1,
2, 3, 4 and 14.

Renames TupleCombinations tests to tuple_comb_* for clarity in test
results.

benches/combinations.rs

@@ -0,0 +1,107 @@
+#![feature(test)]
+
+extern crate test;
+extern crate itertools;
+
+use test::{black_box, Bencher};
+use itertools::Itertools;
+
+// approximate 100_000 iterations for each combination
+const N1: usize = 100_000;
+const N2: usize = 448;
+const N3: usize = 86;
+const N4: usize = 41;
+const N14: usize = 21;
+
+#[bench]
+fn combs_for01(b: &mut Bencher) {
+    b.iter(|| {
+        for i in 0..N1 {
+            black_box(vec![i]);
+        }
+    });
+}
+
+#[bench]
+fn combs_for02(b: &mut Bencher) {
+    b.iter(|| {
+        for i in 0..N2 {
+            for j in (i + 1)..N2 {
+                black_box(vec![i, j]);
+            }
+        }
+    });
+}
+
+#[bench]
+fn combs_for03(b: &mut Bencher) {
+    b.iter(|| {
+        for i in 0..N3 {
+            for j in (i + 1)..N3 {
+                for k in (j + 1)..N3 {
+                    black_box(vec![i, j, k]);
+                }
+            }
+        }
+    });
+}
+
+#[bench]
+fn combs_for04(b: &mut Bencher) {
+    b.iter(|| {
+        for i in 0..N4 {
+            for j in (i + 1)..N4 {
+                for k in (j + 1)..N4 {
+                    for l in (k + 1)..N4 {
+                        black_box(vec![i, j, k, l]);
+                    }
+                }
+            }
+        }
+    });
+}
+
+#[bench]
+fn combs_c01(b: &mut Bencher) {
+    b.iter(|| {
+        for combo in (0..N1).combinations(1) {
+            black_box(combo);
+        }
+    });
+}
+
+#[bench]
+fn combs_c02(b: &mut Bencher) {
+    b.iter(|| {
+        for combo in (0..N2).combinations(2) {
+            black_box(combo);
+        }
+    });
+}
+
+#[bench]
+fn combs_c03(b: &mut Bencher) {
+    b.iter(|| {
+        for combo in (0..N3).combinations(3) {
+            black_box(combo);
+        }
+    });
+}
+
+#[bench]
+fn combs_c04(b: &mut Bencher) {
+    b.iter(|| {
+        for combo in (0..N4).combinations(4) {
+            black_box(combo);
+        }
+    });
+}
+
+#[bench]
+fn combs_c14(b: &mut Bencher) {
+    b.iter(|| {
+        for combo in (0..N14).combinations(14) {
+            black_box(combo);
+        }
+    });
+}

benches/tuple_combinations.rs

@@ -13,7 +13,7 @@ const N3: usize = 86;
 const N4: usize = 41;
 
 #[bench]
-fn comb_for1(b: &mut Bencher) {
+fn tuple_comb_for1(b: &mut Bencher) {
     b.iter(|| {
         for i in 0..N1 {
             black_box(i);
@@ -22,7 +22,7 @@ fn comb_for1(b: &mut Bencher) {
 }
 
 #[bench]
-fn comb_for2(b: &mut Bencher) {
+fn tuple_comb_for2(b: &mut Bencher) {
     b.iter(|| {
         for i in 0..N2 {
             for j in (i + 1)..N2 {
@@ -33,7 +33,7 @@ fn comb_for2(b: &mut Bencher) {
 }
 
 #[bench]
-fn comb_for3(b: &mut Bencher) {
+fn tuple_comb_for3(b: &mut Bencher) {
     b.iter(|| {
         for i in 0..N3 {
             for j in (i + 1)..N3 {
@@ -46,7 +46,7 @@ fn comb_for3(b: &mut Bencher) {
 }
 
 #[bench]
-fn comb_for4(b: &mut Bencher) {
+fn tuple_comb_for4(b: &mut Bencher) {
     b.iter(|| {
         for i in 0..N4 {
             for j in (i + 1)..N4 {
@@ -61,7 +61,7 @@ fn comb_for4(b: &mut Bencher) {
 }
 
 #[bench]
-fn comb_c1(b: &mut Bencher) {
+fn tuple_comb_c1(b: &mut Bencher) {
     b.iter(|| {
         for (i,) in (0..N1).tuple_combinations() {
             black_box(i);
@@ -70,7 +70,7 @@ fn comb_c1(b: &mut Bencher) {
 }
 
 #[bench]
-fn comb_c2(b: &mut Bencher) {
+fn tuple_comb_c2(b: &mut Bencher) {
     b.iter(|| {
         for (i, j) in (0..N2).tuple_combinations() {
             black_box(i + j);
@@ -79,7 +79,7 @@ fn comb_c2(b: &mut Bencher) {
 }
 
 #[bench]
-fn comb_c3(b: &mut Bencher) {
+fn tuple_comb_c3(b: &mut Bencher) {
     b.iter(|| {
         for (i, j, k) in (0..N3).tuple_combinations() {
             black_box(i + j + k);
@@ -88,7 +88,7 @@ fn comb_c3(b: &mut Bencher) {
 }
 
 #[bench]
-fn comb_c4(b: &mut Bencher) {
+fn tuple_comb_c4(b: &mut Bencher) {
     b.iter(|| {
         for (i, j, k, l) in (0..N4).tuple_combinations() {
             black_box(i + j + k + l);