add parse_varint iter benchmark

Author: astro

Diff for: benches/varint_parse.rs

@@ -1,5 +1,5 @@
 extern crate protobuf_iter;
-use protobuf_iter::{Packed, PackedVarint};
+use protobuf_iter::{Packed, PackedVarint, PackedIter};
 
 fn parse_varint(data: &[u8]) {
     let _ = PackedVarint::parse(data).unwrap();
@@ -13,6 +13,31 @@ use criterion::Criterion;
 fn criterion_benchmark(c: &mut Criterion) {
     c.bench_function("parse_varint 1", |b| b.iter(|| parse_varint(&[0b0000_0001])));
     c.bench_function("parse_varint 300", |b| b.iter(|| parse_varint(&[0b1010_1100, 0b0000_0010])));
+
+    let mut buf = Vec::<u8>::new();
+    for i in 0..131073u32 {
+        let mut n = i;
+        let mut bytes = 0;
+        while bytes < 1 || n != 0 {
+            let b = n as u8 & 0b0111_1111;
+            n >>= 7;
+            let flag = if n != 0 {
+                0b1000_0000
+            } else {
+                0
+            };
+            buf.push(flag | b);
+            bytes += 1;
+        }
+    }
+    c.bench_function("parse_varint iter", move |b| b.iter(
+        || {
+            let mut iter: PackedIter<'_, PackedVarint, u32> = PackedIter::new(&buf);
+            for i in 0..131073u32 {
+                assert_eq!(Some(i), iter.next());
+            }
+            assert_eq!(None, iter.next());
+        }));
 }
 
 criterion_group!(benches, criterion_benchmark);