1 files changed, 31 insertions, 0 deletions
diff --git a/deps/v8/src/strings/unicode.cc b/deps/v8/src/strings/unicode.cc
index 0a9b3bbb3d..d98d946f16 100644
--- a/deps/v8/src/strings/unicode.cc
+++ b/deps/v8/src/strings/unicode.cc
@@ -239,6 +239,37 @@ bool Utf8::ValidateEncoding(const byte* bytes, size_t length) {
   return state == State::kAccept;
 }
 
+// static
+void Utf16::ReplaceUnpairedSurrogates(const uint16_t* source_code_units,
+                                      uint16_t* dest_code_units,
+                                      size_t length) {
+  // U+FFFD (REPLACEMENT CHARACTER)
+  constexpr uint16_t kReplacement = 0xFFFD;
+
+  for (size_t i = 0; i < length; i++) {
+    const uint16_t source_code_unit = source_code_units[i];
+    const size_t copy_index = i;
+    uint16_t dest_code_unit = source_code_unit;
+    if (IsLeadSurrogate(source_code_unit)) {
+      // The current code unit is a leading surrogate. If it's not followed by a
+      // trailing surrogate, replace it with the replacement character.
+      if (i == length - 1 || !IsTrailSurrogate(source_code_units[i + 1])) {
+        dest_code_unit = kReplacement;
+      } else {
+        // Copy the paired trailing surrogate. The paired leading surrogate will
+        // be copied below.
+        ++i;
+        dest_code_units[i] = source_code_units[i];
+      }
+    } else if (IsTrailSurrogate(source_code_unit)) {
+      // All paired trailing surrogates are skipped above, so this branch is
+      // only for those that are unpaired.
+      dest_code_unit = kReplacement;
+    }
+    dest_code_units[copy_index] = dest_code_unit;
+  }
+}
+
 #if V8_ENABLE_WEBASSEMBLY
 bool Wtf8::ValidateEncoding(const byte* bytes, size_t length) {
   using State = GeneralizedUtf8DfaDecoder::State;