Add an improved Rust version that iterates chars just once

cuviper · cuviper · commit 7c79b543996d · 2017-11-16T12:40:15.000-08:00
----------------------------------------------------------------------------------------
Name (time in us)             Min                    Max                   Mean
----------------------------------------------------------------------------------------
test_rust_once           694.0350 (1.0)         741.8010 (1.0)         695.5648 (1.0)
test_rust              1,806.4040 (2.60)      1,935.9130 (2.61)      1,812.6250 (2.61)
test_regex            14,219.5200 (20.49)    14,421.8970 (19.44)    14,244.1962 (20.48)
test_pure_python      31,766.5810 (45.77)    52,128.1230 (70.27)    35,289.6043 (50.74)
----------------------------------------------------------------------------------------
diff --git a/doubles_with_rust.py b/doubles_with_rust.py
@@ -32,3 +32,6 @@ def test_regex(benchmark):
 
 def test_rust(benchmark):
     benchmark(myrustlib.count_doubles, val)
+
+def test_rust_once(benchmark):
+    benchmark(myrustlib.count_doubles_once, val)
diff --git a/pyext-myrustlib/src/lib.rs b/pyext-myrustlib/src/lib.rs
@@ -15,8 +15,25 @@ fn count_doubles(_py: Python, val: &str) -> PyResult<u64> {
     Ok(total)
 }
 
+fn count_doubles_once(_py: Python, val: &str) -> PyResult<u64> {
+    let mut total = 0u64;
+
+    let mut chars = val.chars();
+    if let Some(mut c1) = chars.next() {
+        for c2 in chars {
+            if c1 == c2 {
+                total += 1;
+            }
+            c1 = c2;
+        }
+    }
+
+    Ok(total)
+}
+
 py_module_initializer!(libmyrustlib, initlibmyrustlib, PyInit_myrustlib, |py, m | {
     try!(m.add(py, "__doc__", "This module is implemented in Rust"));
     try!(m.add(py, "count_doubles", py_fn!(py, count_doubles(val: &str))));
+    try!(m.add(py, "count_doubles_once", py_fn!(py, count_doubles_once(val: &str))));
     Ok(())
 });
