Add version window constants

ConflictSet.cpp

@@ -78,13 +78,18 @@ constexpr void removeKey(struct Node *) {}
 
 // ==================== BEGIN IMPLEMENTATION ====================
 
+constexpr int64_t kNominalVersionWindow = 2e9;
+constexpr int64_t kMaxCorrectVersionWindow =
+    std::numeric_limits<int32_t>::max();
+static_assert(kNominalVersionWindow <= kMaxCorrectVersionWindow);
+
 struct InternalVersionT {
   constexpr InternalVersionT() = default;
   constexpr explicit InternalVersionT(int64_t value) : value(value) {}
   constexpr int64_t toInt64() const { return value; } // GCOVR_EXCL_LINE
   constexpr auto operator<=>(const InternalVersionT &rhs) const {
     // Maintains ordering after overflow, as long as the full-precision versions
-    // are within ~2e9 of eachother.
+    // are within `kMaxCorrectVersionWindow` of eachother.
     return int32_t(value - rhs.value) <=> 0;
   }
   constexpr bool operator==(const InternalVersionT &) const = default;
@@ -2834,7 +2839,8 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
       auto end = std::span<const uint8_t>(r.end.p, r.end.len);
       result[i] =
           InternalVersionT(reads[i].readVersion) < oldestVersion ||
-                  reads[i].readVersion < newestVersionFullPrecision - 2e9
+                  reads[i].readVersion <
+                      newestVersionFullPrecision - kNominalVersionWindow
               ? TooOld
           : (end.size() > 0
                  ? checkRangeRead(root, begin, end,
@@ -2950,7 +2956,7 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
   InternalVersionT oldestVersion;
   // TODO this doesn't fully mitigate the 32-bit precision issue, since we still
   // need to make sure we clean up versions in the tree before they fall out of
-  // the 2e9 window.
+  // the `kMaxCorrectVersionWindow` window.
   int64_t oldestVersionFullPrecision;
   int64_t newestVersionFullPrecision;
   int64_t totalBytes = 0;