From 930669d8773ce51ed9ca7b24f5b9e1c4c86be7a1 Mon Sep 17 00:00:00 2001
From: yoshi~ <jreusch4@gmail.com>
Date: Wed, 12 Feb 2025 22:15:16 +0100
Subject: [PATCH] first pass split improvements

---
 src/iv.gleam | 71 ++++++++++++++++++++++++++++++----------------------
 1 file changed, 41 insertions(+), 30 deletions(-)

diff --git a/src/iv.gleam b/src/iv.gleam
index 84027a5..db841a0 100644
--- a/src/iv.gleam
+++ b/src/iv.gleam
@@ -2180,9 +2180,7 @@ pub fn split(array: Array(item), at index: Int) -> #(Array(item), Array(item)) {
             Split(prefix:, suffix:) -> {
               #(Array(shift:, root: prefix), Array(shift:, root: suffix))
             }
-            EmptyPrefix(suffix:) -> {
-              #(Empty, Array(shift:, root: suffix))
-            }
+            EmptyPrefix -> #(Empty, array)
           }
       }
   }
@@ -2190,7 +2188,7 @@ pub fn split(array: Array(item), at index: Int) -> #(Array(item), Array(item)) {
 
 type SplitResult(item) {
   Split(prefix: Node(item), suffix: Node(item))
-  EmptyPrefix(suffix: Node(item))
+  EmptyPrefix
 }
 
 fn split_node(shift: Int, node: Node(item), index: Int) -> SplitResult(item) {
@@ -2198,7 +2196,25 @@ fn split_node(shift: Int, node: Node(item), index: Int) -> SplitResult(item) {
     Balanced(children:, ..) -> {
       let node_index = bitwise_shift_right(index, shift)
       let index = index - bitwise_shift_left(node_index, shift)
-      split_children(shift, node_index, index, children)
+
+      let child = vector.get(node_index + 1, children)
+      let child_shift = shift - branch_bits
+      let #(before_children, after_children) =
+        vector.split(node_index + 1, children)
+
+      case split_node(child_shift, child, index) {
+        EmptyPrefix if node_index == 0 -> EmptyPrefix
+        EmptyPrefix -> {
+          let prefix = balanced(shift, before_children)
+          let suffix = balanced(shift, after_children)
+          Split(prefix:, suffix:)
+        }
+        Split(prefix:, suffix:) -> {
+          let prefix = balanced(shift, vector.append(before_children, prefix))
+          let suffix = branch(shift, vector.set(1, after_children, suffix))
+          Split(prefix:, suffix:)
+        }
+      }
     }
     Unbalanced(children:, sizes:) -> {
       let start_search_index = bitwise_shift_right(index, shift)
@@ -2208,11 +2224,29 @@ fn split_node(shift: Int, node: Node(item), index: Int) -> SplitResult(item) {
         // node_index - 1 + 1
         _ -> index - vector.get(node_index, sizes)
       }
-      split_children(shift, node_index, index, children)
+
+      let child = vector.get(node_index + 1, children)
+      let child_shift = shift - branch_bits
+      let #(before_children, after_children) =
+        vector.split(node_index + 1, children)
+
+      case split_node(child_shift, child, index) {
+        EmptyPrefix if node_index == 0 -> EmptyPrefix
+        EmptyPrefix -> {
+          let prefix = branch(shift, before_children)
+          let suffix = branch(shift, after_children)
+          Split(prefix:, suffix:)
+        }
+        Split(prefix:, suffix:) -> {
+          let prefix = branch(shift, vector.append(before_children, prefix))
+          let suffix = branch(shift, vector.set(1, after_children, suffix))
+          Split(prefix:, suffix:)
+        }
+      }
     }
     Leaf(children) ->
       case index {
-        0 -> EmptyPrefix(suffix: node)
+        0 -> EmptyPrefix
         _ -> {
           let #(before, after) = vector.split(index + 1, children)
           Split(prefix: Leaf(before), suffix: Leaf(after))
@@ -2221,29 +2255,6 @@ fn split_node(shift: Int, node: Node(item), index: Int) -> SplitResult(item) {
   }
 }
 
-fn split_children(shift, node_index, index, children) -> SplitResult(item) {
-  let child = vector.get(node_index + 1, children)
-  let child_shift = shift - branch_bits
-  let #(before_children, after_children) =
-    vector.split(node_index + 1, children)
-
-  case split_node(child_shift, child, index) {
-    EmptyPrefix(suffix:) if node_index == 0 -> {
-      EmptyPrefix(suffix: branch(shift, vector.set(1, after_children, suffix)))
-    }
-    EmptyPrefix(suffix:) -> {
-      let prefix = branch(shift, before_children)
-      let suffix = branch(shift, vector.set(1, after_children, suffix))
-      Split(prefix:, suffix:)
-    }
-    Split(prefix:, suffix:) -> {
-      let prefix = branch(shift, vector.append(before_children, prefix))
-      let suffix = branch(shift, vector.set(1, after_children, suffix))
-      Split(prefix:, suffix:)
-    }
-  }
-}
-
 /// Remove up to `n` elements from the start of the array.
 ///
 /// If the array has less than `n` elements an empty array is returned.
-- 
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