Fixed regression in UTF16 decoding (fixes #1173)

src/ArduinoJson/Json/Utf16.hpp

@@ -0,0 +1,49 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#pragma once
+
+#include <ArduinoJson/Namespace.hpp>
+
+#include <stdint.h>  // uint16_t, uint32_t
+
+namespace ARDUINOJSON_NAMESPACE {
+
+namespace Utf16 {
+inline bool isHighSurrogate(uint16_t codeunit) {
+  return codeunit >= 0xD800 && codeunit < 0xDC00;
+}
+
+inline bool isLowSurrogate(uint16_t codeunit) {
+  return codeunit >= 0xDC00 && codeunit < 0xE000;
+}
+
+class Codepoint {
+ public:
+  bool append(uint16_t codeunit) {
+    if (isHighSurrogate(codeunit)) {
+      _highSurrogate = codeunit & 0x3FF;
+      return false;
+    }
+
+    if (isLowSurrogate(codeunit)) {
+      _codepoint =
+          uint32_t(0x10000 + ((_highSurrogate << 10) | (codeunit & 0x3FF)));
+      return true;
+    }
+
+    _codepoint = codeunit;
+    return true;
+  }
+
+  uint32_t value() const {
+    return _codepoint;
+  }
+
+ private:
+  uint16_t _highSurrogate;
+  uint32_t _codepoint;
+};
+}  // namespace Utf16
+}  // namespace ARDUINOJSON_NAMESPACE