Balancing

src/flow/binary/avl.rs

@@ -40,6 +40,21 @@ trait BinaryTreesAvlExt<'a>: BinaryTreesAvl<'a> {
 
 impl<'a, Trees: BinaryTreesAvl<'a>> BinaryTreesAvlExt<'a> for Trees {}
 
+enum Balancing {
+    Balanced,
+    RightBiased,
+    LeftBiased,
+}
+
+fn balancing(hl: u64, hr: u64) -> Balancing {
+    match (hl.saturating_sub(hr), hr.saturating_sub(hl)) {
+        (0, 0) | (0, 1) | (1, 0) => Balancing::Balanced,
+        (0, _) => Balancing::RightBiased,
+        (_, 0) => Balancing::LeftBiased,
+        (_, _) => unreachable!(),
+    }
+}
+
 pub trait BinaryTreesAvl<'a>:
     BinaryTreesHeight<'a> + BinaryTreesTreeOf<'a> + BinaryTreesTryJoin<'a>
 {
@@ -78,9 +93,9 @@ pub trait BinaryTreesAvl<'a>:
         tr: Self::Tree,
     ) -> BTWrap<'a, Self, Self::Node> {
         let (hl, hr) = (self.height(&tl), self.height(&tr));
-        match (hl.saturating_sub(hr), hr.saturating_sub(hl)) {
+        match balancing(hl, hr) {
-            (0, 0) | (0, 1) | (1, 0) => self.try_join(tl, key, tr),
+            Balancing::Balanced => self.try_join(tl, key, tr),
-            (0, _) => self.assume_bind(&tr, |ctx, trl, kr, trr| {
+            Balancing::RightBiased => self.assume_bind(&tr, |ctx, trl, kr, trr| {
                 let (hrl, hrr) = (ctx.height(&trl), ctx.height(&trr));
                 if hrl > hrr {
                     ctx.assume_bind(&trl, |ctx, trll, krl, trlr| {
@@ -90,7 +105,7 @@ pub trait BinaryTreesAvl<'a>:
                     ctx.make_node((T(tl), key, T(trl)), kr, T(trr))
                 }
             }),
-            (_, 0) => self.assume_bind(&tl, |ctx, tll, kl, tlr| {
+            Balancing::LeftBiased => self.assume_bind(&tl, |ctx, tll, kl, tlr| {
                 let (hll, hlr) = (ctx.height(&tll), ctx.height(&tlr));
                 if hll < hlr {
                     ctx.assume_bind(&tlr, |ctx, tlrl, klr, tlrr| {
@@ -100,7 +115,6 @@ pub trait BinaryTreesAvl<'a>:
                     ctx.make_node(T(tll), kl, (T(tlr), key, T(tr)))
                 }
             }),
-            (_, _) => unreachable!(),
         }
     }
 }