Reduce cost of symbol lookup.

Avoid constructing a temporary std::string object while doing the lookup.

PiperOrigin-RevId: 746118518

Author: protobuf-github-bot

src/google/protobuf/descriptor_database.cc

@@ -30,6 +30,7 @@
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_replace.h"
 #include "absl/strings/string_view.h"
+#include "absl/strings/strip.h"
 #include "google/protobuf/descriptor.pb.h"
 #include "google/protobuf/io/coded_stream.h"
 #include "google/protobuf/parse_context.h"
@@ -492,6 +493,18 @@ class EncodedDescriptorDatabase::DescriptorIndex {
       auto p = package(index);
       return absl::StrCat(p, p.empty() ? "" : ".", symbol(index));
     }
+
+    bool IsSubSymbolOf(const DescriptorIndex& index,
+                       absl::string_view super_symbol) const {
+      const auto consume_part = [&](absl::string_view part) {
+        if (!absl::ConsumePrefix(&super_symbol, part)) return false;
+        return super_symbol.empty() || absl::ConsumePrefix(&super_symbol, ".");
+      };
+      if (auto p = package(index); !p.empty()) {
+        if (!consume_part(p)) return false;
+      }
+      return consume_part(symbol(index));
+    }
   };
 
   struct SymbolCompare {
@@ -793,8 +806,7 @@ EncodedDescriptorDatabase::DescriptorIndex::FindSymbolOnlyFlat(
   auto iter =
       FindLastLessOrEqual(&by_symbol_flat_, name, by_symbol_.key_comp());
 
-  return iter != by_symbol_flat_.end() &&
-                 IsSubSymbol(iter->AsString(*this), name)
+  return iter != by_symbol_flat_.end() && iter->IsSubSymbolOf(*this, name)
              ? all_values_[iter->data_offset].value()
              : Value();
 }