From 8c15cb28d0616cd891f73c1253049a169cb6dd8c Mon Sep 17 00:00:00 2001
From: Andrew Noyes <anoyes34@gmail.com>
Date: Thu, 18 Jan 2024 10:34:02 -0800
Subject: [PATCH] Finish addWriteNaive for singleton writes

---
 ConflictSet.cpp | 94 ++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 85 insertions(+), 9 deletions(-)

diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index 963fca6..89dba0e 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -85,7 +85,7 @@ Node *createNode(const Key &key, Node *parent, int64_t pointVersion) {
   result->child[0] = nullptr;
   result->child[1] = nullptr;
   result->parent = parent;
-  result->priority = 0xff & fastRand();
+  result->priority = fastRand();
   result->len = key.len;
   memcpy(result + 1, key.p, key.len);
   return result;
@@ -240,7 +240,6 @@ void lastLeqMulti(Node *root, std::span<Key> keys, Iterator *results) {
   };
 
   fprintf(file, "digraph TreeSet {\n");
-  fprintf(file, " node [fontname=\"Scientifica\"];\n");
   if (node != nullptr) {
     DebugDotPrinter printer{file};
     fprintf(file, "\n");
@@ -248,10 +247,10 @@ void lastLeqMulti(Node *root, std::span<Key> keys, Iterator *results) {
     fprintf(file, "\n");
     for (auto iter = extrema(node, false); iter != nullptr;
          iter = next(iter, true)) {
-      fprintf(file, " k_%.*s [label=\"k=%.*s;p=%u;m=%d;v=%d,r=%d\"];\n",
-              iter->len, (const char *)(iter + 1), iter->len,
-              (const char *)(iter + 1), iter->priority, int(iter->maxVersion),
-              int(iter->pointVersion), int(iter->rangeVersion));
+      fprintf(file, " k_%.*s [label=\"k=%.*s;m=%d;v=%d,r=%d\"];\n", iter->len,
+              (const char *)(iter + 1), iter->len, (const char *)(iter + 1),
+              int(iter->maxVersion), int(iter->pointVersion),
+              int(iter->rangeVersion));
     }
     for (int i = 0; i < printer.id; ++i) {
       fprintf(file, " null%d [shape=point];\n", i);
@@ -272,6 +271,57 @@ void lastLeqMulti(Node *root, std::span<Key> keys, Iterator *results) {
   return Key{itoaBuf, kMaxLength};
 }
 
+// Recompute maxVersion, and propagate up the tree as necessary
+void updateMaxVersion(Node *n) {
+  for (;;) {
+    int64_t maxVersion = std::max(n->pointVersion, n->rangeVersion);
+    for (int i = 0; i < 2; ++i) {
+      maxVersion =
+          std::max(maxVersion, n->child[i] != nullptr ? n->child[i]->maxVersion
+                                                      : maxVersion);
+    }
+    if (n->maxVersion == maxVersion || n->parent == nullptr) {
+      break;
+    }
+    n->maxVersion = maxVersion;
+    n = n->parent;
+  }
+}
+
+Node **rotate(Node **node, bool dir) {
+  // diagram shown for dir == true
+  /*    n
+       /
+      l
+       \
+        lr
+  */
+  assert(node != nullptr);
+  Node *n = *node;
+  assert(n != nullptr);
+  Node *parent = n->parent;
+  Node *l = n->child[!dir];
+  assert(l != nullptr);
+  Node *lr = l->child[dir];
+  n->child[!dir] = lr;
+  if (lr) {
+    lr->parent = n;
+  }
+  l->child[dir] = n;
+  n->parent = l;
+  l->parent = parent;
+  *node = l;
+  /*    l
+         \
+          n
+         /
+        lr
+  */
+  updateMaxVersion(n);
+  updateMaxVersion(l);
+  return &l->child[dir];
+}
+
 } // namespace
 
 struct ConflictSet::Impl {
@@ -307,6 +357,7 @@ struct ConflictSet::Impl {
     Node **current = &root;
     Node *parent = nullptr;
     const auto &key = write.begin;
+    bool inserted = false;
     for (;;) {
       if (*current == nullptr) {
         auto *newNode = createNode(key, parent, write.writeVersion);
@@ -315,11 +366,13 @@ struct ConflictSet::Impl {
         assert(prev != nullptr);
         assert(prev->rangeVersion <= write.writeVersion);
         newNode->rangeVersion = prev->rangeVersion;
+        inserted = true;
         break;
       } else {
-        // TODO this assert won't be valid in the final design
-        assert((*current)->maxVersion <= write.writeVersion);
-        (*current)->maxVersion = write.writeVersion;
+        // This is the key optimization - setting the max version on the way
+        // down the search path so we only have to do one traversal.
+        (*current)->maxVersion =
+            std::max((*current)->maxVersion, write.writeVersion);
         auto c = key <=> **current;
         if (c == 0) {
           (*current)->pointVersion = write.writeVersion;
@@ -329,6 +382,29 @@ struct ConflictSet::Impl {
         current = &((*current)->child[c > 0]);
       }
     }
+    if (inserted) {
+      auto *n = *current;
+      assert(n != nullptr);
+      for (;;) {
+        if (n->parent == nullptr) {
+          break;
+        }
+        const bool dir = n == n->parent->child[1];
+        assert(dir || n == n->parent->child[0]);
+        // p is the address of the pointer to n->parent in the tree
+        Node **p = n->parent->parent == nullptr
+                       ? &root
+                       : &n->parent->parent
+                              ->child[n->parent->parent->child[1] == n->parent];
+        assert(*p == n->parent);
+        if (n->parent->priority < n->priority) {
+          p = rotate(p, !dir);
+          n = (*p)->parent;
+        } else {
+          break;
+        }
+      }
+    }
   }
 
   void addWrites(const WriteRange *writes, int count) {