From bafe1edfa4e0bfb912880c5d847255866916e56c Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Wed, 31 Jan 2024 14:32:25 -0800
Subject: [PATCH] Remove call to memcmp for partial keys

---
 ConflictSet.cpp | 53 ++++++++++++++++++++++++++++---------------------
 1 file changed, 30 insertions(+), 23 deletions(-)

diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index 1bb5540..114d515 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -37,10 +37,10 @@ struct Node {
   Node *parent = nullptr;
   int64_t maxVersion = std::numeric_limits<int64_t>::lowest();
   Entry entry;
-  constexpr static auto kPartialKeyMaxLen = 18;
   int16_t numChildren = 0;
   bool entryPresent = false;
   uint8_t parentsIndex = 0;
+  constexpr static auto kPartialKeyMaxLen = 10;
   uint8_t partialKey[kPartialKeyMaxLen];
   int8_t partialKeyLen = 0;
   /* end section that's copied to the next node */
@@ -748,33 +748,40 @@ std::string_view getSearchPath(Arena &arena, Node *n) {
 Iterator lastLeq(Node *n, const std::span<const uint8_t> key) {
   auto remaining = key;
   for (;;) {
-    Arena arena;
-    int commonLen = std::min<int>(n->partialKeyLen, remaining.size());
-    if (commonLen > Node::kPartialKeyMaxLen) {
-      __builtin_unreachable();
+    if (n->partialKeyLen > 0) {
+      int commonLen = std::min<int>(n->partialKeyLen, remaining.size());
+      for (int i = 0; i < commonLen; ++i) {
+        auto c = n->partialKey[i] <=> remaining[i];
+        if (c == 0) {
+          continue;
+        }
+        if (c > 0) {
+          n = prevPhysical(n);
+        }
+        goto outerLoop;
+      }
+      if (commonLen == n->partialKeyLen) {
+        // partial key matches
+        remaining = remaining.subspan(commonLen, remaining.size() - commonLen);
+      } else if (n->partialKeyLen > int(remaining.size())) {
+        // n is the first physical node greater than remaining, and there's no
+        // eq node
+        n = prevPhysical(n);
+        goto outerLoop;
+      }
     }
-    int c = memcmp(n->partialKey, remaining.data(), commonLen);
-    if (c == 0 && commonLen == n->partialKeyLen) {
-      // partial key matches
-      remaining = remaining.subspan(commonLen, remaining.size() - commonLen);
-    } else if (c < 0 || (c == 0 && n->partialKeyLen < int(remaining.size()))) {
-      // n is the last physical node less than remaining, and there's no eq node
-      break;
-    } else if (c > 0 || (c == 0 && n->partialKeyLen > int(remaining.size()))) {
-      // n is the first physical node greater than remaining, and there's no eq
-      // node
-      n = prevPhysical(n);
-      break;
+    {
+      Arena arena;
+      assert((std::string(getSearchPath(arena, n)) +
+              std::string((const char *)remaining.data(), remaining.size()))
+                 .ends_with(std::string((const char *)key.data(), key.size())));
     }
-    assert((std::string(getSearchPath(arena, n)) +
-            std::string((const char *)remaining.data(), remaining.size()))
-               .ends_with(std::string((const char *)key.data(), key.size())));
     if (remaining.size() == 0) {
       // We've found the physical node corresponding to search path `key`
       if (n->entryPresent) {
         return {n, 0};
       } else {
-        break;
+        goto outerLoop;
       }
     } else {
       int c = getChildLeq(n, remaining[0]);
@@ -790,14 +797,14 @@ Iterator lastLeq(Node *n, const std::span<const uint8_t> key) {
           if (c >= 0) {
             n = getChildExists(n, c);
           } else {
-            break;
+            goto outerLoop;
           }
           c = getChildLeq(n, 255);
         }
-        break;
       }
     }
   }
+outerLoop:
   // Iterate backwards along existing physical nodes until we find a present
   // entry
   for (; !n->entryPresent; n = prevPhysical(n)) {