added a benchmark for the reversed bitreader to guide optimizations

Author: KillingSpark

Cargo.toml

@@ -13,3 +13,11 @@ readme = "Readme.md"
 [dependencies]
 byteorder = "1.3.2"
 twox-hash = { version = "1.5.0", default-features = false }
+
+[dev-dependencies]
+criterion = "0.3"
+rand = "*"
+
+[[bench]]
+name = "reversedbitreader_bench"
+harness = false

benches/reversedbitreader_bench.rs

@@ -0,0 +1,39 @@
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use rand::rngs::ThreadRng;
+use rand::Rng;
+use ruzstd::decoding::bit_reader_reverse::BitReaderReversed;
+
+fn fibonacci(br: &mut BitReaderReversed, accesses: &[usize]) -> u64 {
+    let mut sum = 0;
+    for x in accesses {
+        sum += br.get_bits(*x).unwrap() as u64;
+    }
+    let _ = black_box(br);
+    sum
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let mut rng = rand::thread_rng();
+    let mut rand_vec = vec![];
+    for _ in 0..100000 {
+        rand_vec.push(rng.gen());
+    }
+
+    let mut access_vec = vec![];
+    let mut br = BitReaderReversed::new(&rand_vec);
+    while br.bits_remaining() > 0 {
+        let x = rng.gen_range(1, 20);
+        br.get_bits(x).unwrap();
+        access_vec.push(x);
+    }
+
+    c.bench_function("fib 20", |b| {
+        b.iter(|| {
+            br.reset(&rand_vec);
+            fibonacci(&mut br, &access_vec)
+        })
+    });
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);