stdlib: Tests for mbrtoc8, c8rtomb, and the char8_t typedef.

This change adds tests for the mbrtoc8 and c8rtomb functions adopted for
C++20 via WG21 P0482R6 and for C2X via WG14 N2653, and for the char8_t
typedef adopted for C2X from WG14 N2653.

The tests for mbrtoc8 and c8rtomb specifically exercise conversion to
and from Big5-HKSCS because of special cases that arise with that encoding.
Big5-HKSCS defines some double byte sequences that convert to more than
one Unicode code point.  In order to test this, the locale dependencies
for running tests under wcsmbs is expanded to include zh_HK.BIG5-HKSCS.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

3 files changed, 1154 insertions, 1 deletions

diff --git a/wcsmbs/Makefile b/wcsmbs/Makefile
index bda281a..e6b9e87 100644
--- a/wcsmbs/Makefile
+++ b/wcsmbs/Makefile
@@ -52,6 +52,7 @@ tests := tst-wcstof wcsmbs-tst1 tst-wcsnlen tst-btowc tst-mbrtowc \
 	 tst-c16c32-1 wcsatcliff tst-wcstol-locale tst-wcstod-nan-locale \
 	 tst-wcstod-round test-char-types tst-fgetwc-after-eof \
 	 tst-wcstod-nan-sign tst-c16-surrogate tst-c32-state \
+	 test-mbrtoc8 test-c8rtomb \
 	 $(addprefix test-,$(strop-tests)) tst-mbstowcs \
 	 tst-wprintf-binary
 
@@ -59,7 +60,7 @@ include ../Rules
 
 ifeq ($(run-built-tests),yes)
 LOCALES := de_DE.ISO-8859-1 de_DE.UTF-8 en_US.ANSI_X3.4-1968 hr_HR.ISO-8859-2 \
-	   ja_JP.EUC-JP zh_TW.EUC-TW tr_TR.UTF-8 tr_TR.ISO-8859-9
+	   ja_JP.EUC-JP zh_TW.EUC-TW tr_TR.UTF-8 tr_TR.ISO-8859-9 zh_HK.BIG5-HKSCS
 include ../gen-locales.mk
 
 $(objpfx)tst-btowc.out: $(gen-locales)
diff --git a/wcsmbs/test-c8rtomb.c b/wcsmbs/test-c8rtomb.c
new file mode 100644
index 0000000..6d72189
--- /dev/null
+++ b/wcsmbs/test-c8rtomb.c
@@ -0,0 +1,613 @@
+/* Test c8rtomb.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <limits.h>
+#include <locale.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <uchar.h>
+#include <wchar.h>
+#include <support/check.h>
+#include <support/support.h>
+
+static int
+test_truncated_code_unit_sequence (void)
+{
+  /* Missing trailing code unit for a two code byte unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xC2";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Missing first trailing code unit for a three byte code unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xE0";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Missing second trailing code unit for a three byte code unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xE0\xA0";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Missing first trailing code unit for a four byte code unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xF0";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Missing second trailing code unit for a four byte code unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xF0\x90";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Missing third trailing code unit for a four byte code unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xF0\x90\x80";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t)  0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[3], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  return 0;
+}
+
+static int
+test_invalid_trailing_code_unit_sequence (void)
+{
+  /* Invalid trailing code unit for a two code byte unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xC2\xC0";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Invalid first trailing code unit for a three byte code unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xE0\xC0";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Invalid second trailing code unit for a three byte code unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xE0\xA0\xC0";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Invalid first trailing code unit for a four byte code unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xF0\xC0";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Invalid second trailing code unit for a four byte code unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xF0\x90\xC0";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Invalid third trailing code unit for a four byte code unit sequence.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xF0\x90\x80\xC0";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t)  0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[3], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  return 0;
+}
+
+static int
+test_lone_trailing_code_units (void)
+{
+  /* Lone trailing code unit.  */
+  const char8_t *u8s = (const char8_t*) u8"\x80";
+  char buf[MB_LEN_MAX] = { 0 };
+  mbstate_t s = { 0 };
+
+  errno = 0;
+  TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) -1);
+  TEST_COMPARE (errno, EILSEQ);
+
+  return 0;
+}
+
+static int
+test_overlong_encoding (void)
+{
+  /* Two byte overlong encoding.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xC0\x80";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Two byte overlong encoding.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xC1\x80";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Three byte overlong encoding.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xE0\x9F\xBF";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Four byte overlong encoding.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xF0\x8F\xBF\xBF";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  return 0;
+}
+
+static int
+test_surrogate_range (void)
+{
+  /* Would encode U+D800.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xED\xA0\x80";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Would encode U+DFFF.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xED\xBF\xBF";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  return 0;
+}
+
+static int
+test_out_of_range_encoding (void)
+{
+  /* Would encode U+00110000.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xF4\x90\x80\x80";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  /* Would encode U+00140000.  */
+  {
+    const char8_t *u8s = (const char8_t*) u8"\xF5\x90\x80\x80";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    errno = 0;
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  return 0;
+}
+
+static int
+test_null_output_buffer (void)
+{
+  /* Null character with an initial state.  */
+  {
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (NULL, u8"X"[0], &s), (size_t) 1);
+    /* Assert the state is now an initial state.  */
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Null buffer with a state corresponding to an incompletely read code
+     unit sequence.  In this case, an error occurs since insufficient
+     information is available to complete the already started code unit
+     sequence and return to the initial state.  */
+  {
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8"\xC2"[0], &s), (size_t)  0);
+    errno = 0;
+    TEST_COMPARE (c8rtomb (NULL, u8"\x80"[0], &s), (size_t) -1);
+    TEST_COMPARE (errno, EILSEQ);
+  }
+
+  return 0;
+}
+
+static int
+test_utf8 (void)
+{
+  xsetlocale (LC_ALL, "de_DE.UTF-8");
+
+  /* Null character.  */
+  {
+    /* U+0000 => 0x00 */
+    const char8_t *u8s = (const char8_t*) u8"\x00";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 1);
+    TEST_COMPARE (buf[0], (char) 0x00);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* First non-null character in the code point range that maps to a single
+     code unit.  */
+  {
+    /* U+0001 => 0x01 */
+    const char8_t *u8s = (const char8_t*) u8"\x01";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 1);
+    TEST_COMPARE (buf[0], (char) 0x01);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Last character in the code point range that maps to a single code unit.  */
+  {
+    /* U+007F => 0x7F */
+    const char8_t *u8s = (const char8_t*) u8"\x7F";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 1);
+    TEST_COMPARE (buf[0], (char) 0x7F);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* First character in the code point range that maps to two code units.  */
+  {
+    /* U+0080 => 0xC2 0x80 */
+    const char8_t *u8s = (const char8_t*) u8"\xC2\x80";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 2);
+    TEST_COMPARE (buf[0], (char) 0xC2);
+    TEST_COMPARE (buf[1], (char) 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Last character in the code point range that maps to two code units.  */
+  {
+    /* U+07FF => 0xDF 0xBF */
+    const char8_t *u8s = (const char8_t*) u8"\u07FF";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 2);
+    TEST_COMPARE (buf[0], (char) 0xDF);
+    TEST_COMPARE (buf[1], (char) 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* First character in the code point range that maps to three code units.  */
+  {
+    /* U+0800 => 0xE0 0xA0 0x80 */
+    const char8_t *u8s = (const char8_t*) u8"\u0800";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) 3);
+    TEST_COMPARE (buf[0], (char) 0xE0);
+    TEST_COMPARE (buf[1], (char) 0xA0);
+    TEST_COMPARE (buf[2], (char) 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Last character in the code point range that maps to three code units
+     before the surrogate code point range.  */
+  {
+    /* U+D7FF => 0xED 0x9F 0xBF */
+    const char8_t *u8s = (const char8_t*) u8"\uD7FF";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) 3);
+    TEST_COMPARE (buf[0], (char) 0xED);
+    TEST_COMPARE (buf[1], (char) 0x9F);
+    TEST_COMPARE (buf[2], (char) 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* First character in the code point range that maps to three code units
+     after the surrogate code point range.  */
+  {
+    /* U+E000 => 0xEE 0x80 0x80 */
+    const char8_t *u8s = (const char8_t*) u8"\uE000";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) 3);
+    TEST_COMPARE (buf[0], (char) 0xEE);
+    TEST_COMPARE (buf[1], (char) 0x80);
+    TEST_COMPARE (buf[2], (char) 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Not a BOM.  */
+  {
+    /* U+FEFF => 0xEF 0xBB 0xBF */
+    const char8_t *u8s = (const char8_t*) u8"\uFEFF";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) 3);
+    TEST_COMPARE (buf[0], (char) 0xEF);
+    TEST_COMPARE (buf[1], (char) 0xBB);
+    TEST_COMPARE (buf[2], (char) 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Replacement character.  */
+  {
+    /* U+FFFD => 0xEF 0xBF 0xBD */
+    const char8_t *u8s = (const char8_t*) u8"\uFFFD";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) 3);
+    TEST_COMPARE (buf[0], (char) 0xEF);
+    TEST_COMPARE (buf[1], (char) 0xBF);
+    TEST_COMPARE (buf[2], (char) 0xBD);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Last character in the code point range that maps to three code units.  */
+  {
+    /* U+FFFF => 0xEF 0xBF 0xBF */
+    const char8_t *u8s = (const char8_t*) u8"\uFFFF";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) 3);
+    TEST_COMPARE (buf[0], (char) 0xEF);
+    TEST_COMPARE (buf[1], (char) 0xBF);
+    TEST_COMPARE (buf[2], (char) 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* First character in the code point range that maps to four code units.  */
+  {
+    /* U+10000 => 0xF0 0x90 0x80 0x80 */
+    const char8_t *u8s = (const char8_t*) u8"\U00010000";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[3], &s), (size_t) 4);
+    TEST_COMPARE (buf[0], (char) 0xF0);
+    TEST_COMPARE (buf[1], (char) 0x90);
+    TEST_COMPARE (buf[2], (char) 0x80);
+    TEST_COMPARE (buf[3], (char) 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Last character in the code point range that maps to four code units.  */
+  {
+    /* U+10FFFF => 0xF4 0x8F 0xBF 0xBF */
+    const char8_t *u8s = (const char8_t*) u8"\U0010FFFF";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[3], &s), (size_t) 4);
+    TEST_COMPARE (buf[0], (char) 0xF4);
+    TEST_COMPARE (buf[1], (char) 0x8F);
+    TEST_COMPARE (buf[2], (char) 0xBF);
+    TEST_COMPARE (buf[3], (char) 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  return 0;
+}
+
+static int
+test_big5_hkscs (void)
+{
+  xsetlocale (LC_ALL, "zh_HK.BIG5-HKSCS");
+
+  /* A pair of two byte UTF-8 code unit sequences that map a Unicode code
+     point and combining character to a single double byte character.  */
+  {
+    /* U+00CA U+0304 => 0x88 0x62 */
+    const char8_t *u8s = (const char8_t*) u8"\u00CA\u0304";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[3], &s), (size_t) 2);
+    TEST_COMPARE (buf[0], (char) 0x88);
+    TEST_COMPARE (buf[1], (char) 0x62);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Another pair of two byte UTF-8 code unit sequences that map a Unicode code
+     point and combining character to a single double byte character.  */
+  {
+    /* U+00EA U+030C => 0x88 0xA5 */
+    const char8_t *u8s = (const char8_t*) u8"\u00EA\u030C";
+    char buf[MB_LEN_MAX] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (c8rtomb (buf, u8s[0], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[1], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[2], &s), (size_t) 0);
+    TEST_COMPARE (c8rtomb (buf, u8s[3], &s), (size_t) 2);
+    TEST_COMPARE (buf[0], (char) 0x88);
+    TEST_COMPARE (buf[1], (char) 0xA5);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  return 0;
+}
+
+static int
+do_test (void)
+{
+  test_truncated_code_unit_sequence ();
+  test_invalid_trailing_code_unit_sequence ();
+  test_lone_trailing_code_units ();
+  test_overlong_encoding ();
+  test_surrogate_range ();
+  test_out_of_range_encoding ();
+  test_null_output_buffer ();
+  test_utf8 ();
+  test_big5_hkscs ();
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/wcsmbs/test-mbrtoc8.c b/wcsmbs/test-mbrtoc8.c
new file mode 100644
index 0000000..16d73e2
--- /dev/null
+++ b/wcsmbs/test-mbrtoc8.c
@@ -0,0 +1,539 @@
+/* Test mbrtoc8.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <locale.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <uchar.h>
+#include <wchar.h>
+#include <support/check.h>
+#include <support/support.h>
+
+static int
+test_utf8 (void)
+{
+  xsetlocale (LC_ALL, "de_DE.UTF-8");
+
+  /* No inputs.  */
+  {
+    const char *mbs = "";
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 0, &s), (size_t) -2); /* no input */
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Null character.  */
+  {
+    const char *mbs = "\x00"; /* 0x00 => U+0000 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 0);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0x00);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* First non-null character in the code point range that maps to a single
+     code unit.  */
+  {
+    const char *mbs = "\x01"; /* 0x01 => U+0001 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0x01);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Last character in the code point range that maps to a single code unit.  */
+  {
+    const char *mbs = "\x7F"; /* 0x7F => U+007F */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0x7F);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* First character in the code point range that maps to two code units.  */
+  {
+    const char *mbs = "\xC2\x80"; /* 0xC2 0x80 => U+0080 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 2);
+    mbs += 2;
+    TEST_COMPARE (buf[0], 0xC2);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\xC2\x80"; /* 0xC2 0x80 => U+0080 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xC2);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Last character in the code point range that maps to two code units.  */
+  {
+    const char *mbs = "\xDF\xBF"; /* 0xDF 0xBF => U+07FF */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 2);
+    mbs += 2;
+    TEST_COMPARE (buf[0], 0xDF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\xDF\xBF"; /* 0xDF 0xBF => U+07FF */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xDF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* First character in the code point range that maps to three code units.  */
+  {
+    const char *mbs = u8"\xE0\xA0\x80"; /* 0xE0 0xA0 0x80 => U+0800 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 3);
+    mbs += 3;
+    TEST_COMPARE (buf[0], 0xE0);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xA0);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = u8"\xE0\xA0\x80"; /* 0xE0 0xA0 0x80 => U+0800 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xE0);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xA0);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Last character in the code point range that maps to three code units
+     before the surrogate code point range.  */
+  {
+    const char *mbs = "\xED\x9F\xBF"; /* 0xED 0x9F 0xBF => U+D7FF */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 3);
+    mbs += 3;
+    TEST_COMPARE (buf[0], 0xED);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x9F);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\xED\x9F\xBF"; /* 0xED 0x9F 0xBF => U+D7FF */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xED);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x9F);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* First character in the code point range that maps to three code units
+     after the surrogate code point range.  */
+  {
+    const char *mbs = "\xEE\x80\x80"; /* 0xEE 0x80 0x80 => U+E000 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 3);
+    mbs += 3;
+    TEST_COMPARE (buf[0], 0xEE);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\xEE\x80\x80"; /* 0xEE 0x80 0x80 => U+E000 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xEE);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Not a BOM.  */
+  {
+    const char *mbs = "\xEF\xBB\xBF"; /* 0xEF 0xBB 0xBF => U+FEFF */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 3);
+    mbs += 3;
+    TEST_COMPARE (buf[0], 0xEF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBB);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\xEF\xBB\xBF"; /* 0xEF 0xBB 0xBF => U+FEFF */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xEF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBB);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Replacement character.  */
+  {
+    const char *mbs = "\xEF\xBF\xBD"; /* 0xEF 0xBF 0xBD => U+FFFD */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 3);
+    mbs += 3;
+    TEST_COMPARE (buf[0], 0xEF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBD);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\xEF\xBF\xBD"; /* 0xEF 0xBF 0xBD => U+FFFD */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xEF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBD);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Last character in the code point range that maps to three code units.  */
+  {
+    const char *mbs = "\xEF\xBF\xBF"; /* 0xEF 0xBF 0xBF => U+FFFF */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 3);
+    mbs += 3;
+    TEST_COMPARE (buf[0], 0xEF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\xEF\xBF\xBF"; /* 0xEF 0xBF 0xBF => U+FFFF */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xEF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* First character in the code point range that maps to four code units.  */
+  {
+    const char *mbs = "\xF0\x90\x80\x80"; /* 0xF0 0x90 0x80 0x80 => U+10000 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 4);
+    mbs += 4;
+    TEST_COMPARE (buf[0], 0xF0);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x90);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\xF0\x90\x80\x80"; /* 0xF0 0x90 0x80 0x80 => U+10000 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xF0);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x90);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x80);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Last character in the code point range that maps to four code units.  */
+  {
+    const char *mbs = "\xF4\x8F\xBF\xBF"; /* 0xF4 0x8F 0xBF 0xBF => U+10FFFF */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 4);
+    mbs += 4;
+    TEST_COMPARE (buf[0], 0xF4);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x8F);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\xF4\x8F\xBF\xBF"; /* 0xF4 0x8F 0xBF 0xBF => U+10FFFF */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xF4);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x8F);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xBF);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  return 0;
+}
+
+static int
+test_big5_hkscs (void)
+{
+  xsetlocale (LC_ALL, "zh_HK.BIG5-HKSCS");
+
+  /* A double byte character that maps to a pair of two byte UTF-8 code unit
+     sequences.  */
+  {
+    const char *mbs = "\x88\x62"; /* 0x88 0x62 => U+00CA U+0304 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 2);
+    mbs += 2;
+    TEST_COMPARE (buf[0], 0xC3);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x8A);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xCC);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x84);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\x88\x62"; /* 0x88 0x62 => U+00CA U+0304 */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xC3);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x8A);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xCC);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x84);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Another double byte character that maps to a pair of two byte UTF-8 code
+     unit sequences.  */
+  {
+    const char *mbs = "\x88\xA5"; /* 0x88 0xA5 => U+00EA U+030C */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) 2);
+    mbs += 2;
+    TEST_COMPARE (buf[0], 0xC3);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xAA);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xCC);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, strlen (mbs) + 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x8C);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  /* Same as last test, but one code unit at a time.  */
+  {
+    const char *mbs = "\x88\xA5"; /* 0x88 0xA5 => U+00EA U+030C */
+    char8_t buf[1] = { 0 };
+    mbstate_t s = { 0 };
+
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -2);
+    mbs += 1;
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) 1);
+    mbs += 1;
+    TEST_COMPARE (buf[0], 0xC3);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xAA);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0xCC);
+    TEST_COMPARE (mbrtoc8 (buf, mbs, 1, &s), (size_t) -3);
+    TEST_COMPARE (buf[0], 0x8C);
+    TEST_VERIFY (mbsinit (&s));
+  }
+
+  return 0;
+}
+
+static int
+do_test (void)
+{
+  test_utf8 ();
+  test_big5_hkscs ();
+  return 0;
+}
+
+#include <support/test-driver.c>