1 files changed, 38 insertions, 3 deletions
diff --git a/wcsmbs/c16rtomb.c b/wcsmbs/c16rtomb.c
index 48a63d067b..74950d8173 100644
--- a/wcsmbs/c16rtomb.c
+++ b/wcsmbs/c16rtomb.c
@@ -26,7 +26,42 @@ static mbstate_t state;
 size_t
 c16rtomb (char *s, char16_t c16, mbstate_t *ps)
 {
-  // XXX The ISO C 11 spec I have does not say anything about handling
-  // XXX surrogates in this interface.
-  return wcrtomb (s, c16, ps ?: &state);
+  wchar_t wc = c16;
+
+  if (ps == NULL)
+    ps = &state;
+
+  if (s == NULL)
+    {
+      /* Reset any state relating to surrogate pairs.  */
+      ps->__count &= 0x7fffffff;
+      ps->__value.__wch = 0;
+      wc = 0;
+    }
+
+  if (ps->__count & 0x80000000)
+    {
+      /* The previous call passed in the first surrogate of a
+	 surrogate pair.  */
+      ps->__count &= 0x7fffffff;
+      if (wc >= 0xdc00 && wc < 0xe000)
+	wc = (0x10000
+	      + ((ps->__value.__wch & 0x3ff) << 10)
+	      + (wc & 0x3ff));
+      else
+	/* This is not a low surrogate; ensure an EILSEQ error by
+	   trying to decode the high surrogate as a wide character on
+	   its own.  */
+	wc = ps->__value.__wch;
+      ps->__value.__wch = 0;
+    }
+  else if (wc >= 0xd800 && wc < 0xdc00)
+    {
+      /* The high part of a surrogate pair.  */
+      ps->__count |= 0x80000000;
+      ps->__value.__wch = wc;
+      return 0;
+    }
+
+  return wcrtomb (s, wc, ps);
 }