- for (f = s, t = r; f < (const uint8_t*) s + length; f += 2)
- t += utf8_encode_unichar(t, (f[1] << 8) | f[0]);
+ f = s;
+ t = r;
+
+ while (f < (const uint8_t*) s + length) {
+ uint16_t w1, w2;
+
+ /* see RFC 2781 section 2.2 */
+
+ w1 = f[1] << 8 | f[0];
+ f += 2;
+
+ if (!utf16_is_surrogate(w1)) {
+ t += utf8_encode_unichar(t, w1);
+
+ continue;
+ }
+
+ if (utf16_is_trailing_surrogate(w1))
+ continue;
+ else if (f >= (const uint8_t*) s + length)
+ break;
+
+ w2 = f[1] << 8 | f[0];
+ f += 2;
+
+ if (!utf16_is_trailing_surrogate(w2)) {
+ f -= 2;
+ continue;
+ }
+
+ t += utf8_encode_unichar(t, utf16_surrogate_pair_to_unichar(w1, w2));
+ }