drain_inverse improve performance

src/ext.rs

@@ -25,25 +25,62 @@ pub trait FindSliceBounds
 
 pub trait SliceInPlace
 {
-    fn slice_in_place(&mut self, slice: Range<usize>);
+    #[deprecated = "Slow. Use `drain_inverse`"]
+    #[inline] 
+    fn slice_in_place<R: std::ops::RangeBounds<usize>>(&mut self, slice: R)
+    {
+	self.drain_inverse(slice);
+    }
+    fn drain_inverse<R: std::ops::RangeBounds<usize>>(&mut self, slice: R);
 }
 
 impl SliceInPlace for String
 {
-    fn slice_in_place(&mut self, slice: Range<usize>) {
+    fn slice_in_place<R: std::ops::RangeBounds<usize>>(&mut self, slice: R) {
 	let mut i=0;
 	self.retain(|_| (slice.contains(&i), i+=1).0);
     }
+    
+    fn drain_inverse<R: std::ops::RangeBounds<usize>>(&mut self, slice: R)
+    {
+	use std::ops::Bound;
+	match slice.end_bound() {
+	    Bound::Excluded(&ex) => drop(self.drain(ex..)),
+	    Bound::Included(&inc) => drop(self.drain(inc+1..)),
+	    _ => (),
+	};
+	match slice.start_bound() {
+	    Bound::Included(&ex) => drop(self.drain(..ex)),
+	    Bound::Excluded(&ex) => drop(..ex+1),
+	    _ => ()
+	};
+    }
 }
 
 impl<T> SliceInPlace for Vec<T>
 {
-    fn slice_in_place(&mut self, slice: Range<usize>) {
+    fn slice_in_place<R: std::ops::RangeBounds<usize>>(&mut self, slice: R) {
 	let mut i=0;
 	self.retain(|_| (slice.contains(&i), i+=1).0);
     }
+    
+    fn drain_inverse<R: std::ops::RangeBounds<usize>>(&mut self, slice: R)
+    {
+	use std::ops::Bound;
+	match slice.end_bound() {
+	    Bound::Excluded(&ex) => drop(self.drain(ex..)),
+	    Bound::Included(&inc) => drop(self.drain(inc+1..)),
+	    _ => (),
+	};
+	match slice.start_bound() {
+	    Bound::Included(&ex) => drop(self.drain(..ex)),
+	    Bound::Excluded(&ex) => drop(..ex+1),
+	    _ => ()
+	};
+    }
 }
 
+
 impl<T: ?Sized + AsRef<str>> FindSliceBounds for T
 {
     type SliceType = str;
@@ -72,6 +109,8 @@ impl<T: ?Sized + AsRef<str>> FindSliceBounds for T
 #[cfg(test)]
 mod test_slice_in_place
 {
+    use test::{Bencher, black_box};
+    
     use super::*;
     #[test]
     fn slice_in_place_str()
@@ -85,6 +124,36 @@ mod test_slice_in_place
 	assert_eq!(&string[string.slice_bounds(string.trim())], string.trim());
 	assert_eq!(&string[string.slice_bounds(string.trim())], "hello world");
     }
+
+    #[bench]
+    fn bench_slice_in_place(b: &mut Bencher)
+    {
+	let mut string = String::from("hello ONE TWO world");
+	b.iter(|| {
+	    black_box(string.slice_in_place(7..16));
+	    string.push_str("ONE TWO");
+	});
+    }
+    
+    #[bench]
+    fn bench_drain_inverse(b: &mut Bencher)
+    {
+	let mut string = String::from("hello ONE TWO world");
+	b.iter(|| {
+	    black_box(string.drain_inverse(7..16));
+	    string.push_str("ONE TWO");
+	});
+    }
+
+    #[test]
+    fn drain_inverse()
+    {
+	let mut string = String::from("123hello world5678");
+	string.drain_inverse(3..=13);
+	assert_eq!(&string[..], "hello world");
+	string.drain_inverse(6..);
+	assert_eq!(&string[..], "world");
+    }
 }
 
 

src/format/key/mod.rs

@@ -274,7 +274,7 @@ impl KeyHeader
 		    }
 		    buffer.slice_bounds(trimmed)
 		};
-		buffer.slice_in_place(bounds);
+		buffer.drain_inverse(bounds);
 		if {
 		    let bytes = buffer.as_bytes();