UCS2 conversion for unreal

luprex/cpp/drv/drvutil.cpp

@@ -194,6 +194,30 @@ std::u32string from_utf8(std::string_view s, int *consumed) {
     return result.substr(0, len);
 }
 
+std::u16string utf8_to_ucs2(std::string_view s, int *consumed) {
+    std::string_view rest = s;
+    std::u16string result(s.size(), 0);
+    int len = 0;
+    while (true) {
+        int32_t c = read_codepoint_utf8(rest);
+        if (c == -1) {
+            break; // EOF reached;
+        } else if (c < 0) {
+            rest.remove_prefix(1);
+        } else if ((c >= 0xD800) && (c <= 0xDFFF)) {
+            result[len++] = 0x2610;
+        } else if (c > 0xFFFF) {
+            result[len++] = 0x2610;
+        } else {
+            result[len++] = (char16_t)c;
+        }
+    }
+    if (consumed != nullptr) {
+        *consumed = s.size() - rest.size();
+    }
+    return result.substr(0, len);
+}
+
 static std::vector<std::string> parse_control_lst(std::string_view ctrl) {
     std::vector<std::string> result;
     while (!ctrl.empty()) {

luprex/cpp/drv/drvutil.hpp

@@ -63,6 +63,10 @@ std::string to_utf8(const std::u32string &cps);
 //
 std::u32string from_utf8(std::string_view source, int *consumed);
 
+// Convert a UTF8 string to a UCS-2 string.
+//
+std::u16string utf8_to_ucs2(std::string_view source, int *consumed);
+
 // Get a system error message, in an OS-independent manner.
 //
 // These versions of strerror is thread-safe, and it never fails