From c882d7663de9f90084fe95d455d4aae395d41f88 Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Wed, 26 Jun 2024 18:57:08 -0700
Subject: [PATCH] Maintain "reverseIndex" in Node48

---
 ConflictSet.cpp | 60 ++++++++++++++++++-------------------------------
 1 file changed, 22 insertions(+), 38 deletions(-)

diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index 074cf2d..a5404bd 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -294,8 +294,7 @@ struct Node48 : Node {
   int8_t nextFree;
   int8_t index[256];
   Child children[kMaxNodes];
-  // Max of each "page" of 16 children
-  int64_t maxOfMax[16];
+  uint8_t reverseIndex[kMaxNodes];
 
   uint8_t *partialKey() { return (uint8_t *)(this + 1); }
 
@@ -419,7 +418,7 @@ inline void Node48::copyChildrenAndKeyFrom(const Node16 &other) {
     children[i] = other.children[i];
     assert(children[i].child->parent == &other);
     children[i].child->parent = this;
-    maxOfMax[x >> 4] = std::max(maxOfMax[x >> 4], children[i].childMaxVersion);
+    reverseIndex[i] = x;
     ++i;
   }
 }
@@ -434,7 +433,7 @@ inline void Node48::copyChildrenAndKeyFrom(const Node48 &other) {
     assert(children[i].child->parent == &other);
     children[i].child->parent = this;
   }
-  memcpy(maxOfMax, other.maxOfMax, sizeof(maxOfMax));
+  memcpy(reverseIndex, other.reverseIndex, sizeof(reverseIndex));
   memcpy(partialKey(), &other + 1, partialKeyLen);
 }
 
@@ -454,10 +453,10 @@ inline void Node48::copyChildrenAndKeyFrom(const Node256 &other) {
         children[i] = other.children[c];
         assert(children[i].child->parent == &other);
         children[i].child->parent = this;
+        reverseIndex[i] = c;
         ++i;
       },
       0, 256);
-  memcpy(maxOfMax, other.maxOfMax, sizeof(maxOfMax));
   memcpy(partialKey(), &other + 1, partialKeyLen);
 }
 
@@ -472,9 +471,10 @@ inline void Node256::copyChildrenAndKeyFrom(const Node48 &other) {
         children[c] = other.children[other.index[c]];
         assert(children[c].child->parent == &other);
         children[c].child->parent = this;
+        maxOfMax[c >> 4] =
+            std::max(maxOfMax[c >> 4], children[c].childMaxVersion);
       },
       0, 256);
-  memcpy(maxOfMax, other.maxOfMax, sizeof(maxOfMax));
   memcpy(partialKey(), &other + 1, partialKeyLen);
 }
 
@@ -575,7 +575,7 @@ template <class T> struct BoundedFreeListAllocator {
     if constexpr (!std::is_same_v<T, Node0>) {
       memset(result->children, 0, sizeof(result->children));
     }
-    if constexpr (std::is_same_v<T, Node48> || std::is_same_v<T, Node256>) {
+    if constexpr (std::is_same_v<T, Node256>) {
       memset(result->maxOfMax, 0, sizeof(result->maxOfMax));
     }
     return result;
@@ -1047,6 +1047,7 @@ Node *&getOrCreateChild(Node *&self, uint8_t index,
     assert(self48->nextFree < 48);
     int nextFree = self48->nextFree++;
     self48->index[index] = nextFree;
+    self48->reverseIndex[nextFree] = index;
     auto &result = self48->children[nextFree].child;
     result = nullptr;
     return result;
@@ -1346,8 +1347,10 @@ Node *erase(Node *self, NodeAllocators *allocators, ConflictSet::Impl *impl,
     if (toRemoveChildrenIndex != lastChildrenIndex) {
       parent48->children[toRemoveChildrenIndex] =
           parent48->children[lastChildrenIndex];
-      parent48->index[parent48->children[toRemoveChildrenIndex]
-                          .child->parentsIndex] = toRemoveChildrenIndex;
+      auto parentIndex =
+          parent48->children[toRemoveChildrenIndex].child->parentsIndex;
+      parent48->index[parentIndex] = toRemoveChildrenIndex;
+      parent48->reverseIndex[toRemoveChildrenIndex] = parentIndex;
     }
 
     --parent->numChildren;
@@ -1692,36 +1695,18 @@ bool checkMaxBetweenExclusive(Node *n, int begin, int end,
   } break;
   case Type_Node48: {
     auto *self = static_cast<Node48 *>(n);
-    // Check the first page
-    if (self->maxOfMax[begin >> 4] > readVersion) {
-      bool result = true;
-      self->bitSet.forEachInRange(
-          [&](int i) {
-            result &=
-                self->children[self->index[i]].childMaxVersion <= readVersion;
-          },
-          begin, std::min((begin & ~15) + 16, end));
-      if (!result) {
-        return result;
-      }
+    bool conflict[Node48::kMaxNodes] = {};
+    assume(self->numChildren >= kMinChildrenNode48 - 1 /* entry present */);
+    assume(self->numChildren <= Node48::kMaxNodes);
+    for (int i = 0; i < self->numChildren; ++i) {
+      assert(self->index[self->reverseIndex[i]] == i);
+      conflict[i] = (begin <= self->reverseIndex[i]) &
+                    (self->reverseIndex[i] < end) &
+                    (self->children[i].childMaxVersion > readVersion);
     }
-    // Check the last page
-    if (end >= 1 && self->maxOfMax[(end - 1) >> 4] > readVersion) {
-      bool result = true;
-      self->bitSet.forEachInRange(
-          [&](int i) {
-            result &=
-                self->children[self->index[i]].childMaxVersion <= readVersion;
-          },
-          std::max(begin, end & ~15), end);
-      if (!result) {
-        return result;
-      }
-    }
-    // Check inner pages
     bool result = true;
-    for (int i = (begin >> 4) + 1; i < (end - 1) >> 4; ++i) {
-      result &= self->maxOfMax[i] <= readVersion;
+    for (auto c : conflict) {
+      result &= !c;
     }
     return result;
   }
@@ -2685,7 +2670,6 @@ void setMaxVersion(Node *n, ConflictSet::Impl *impl, int64_t newMax) {
     auto *n48 = static_cast<Node48 *>(n);
     assert(n48->bitSet.test(index));
     n48->children[n48->index[index]].childMaxVersion = newMax;
-    n48->maxOfMax[index >> 4] = std::max(n48->maxOfMax[index >> 4], newMax);
     return;
   }
   case Type_Node256: {