Add `scm_{to,from}_utf32_string'.

* libguile/strings.c (scm_from_utf32_string, scm_from_utf32_stringn,
  scm_to_utf32_string, scm_to_utf32_stringn): New functions.

* libguile/strings.h (scm_from_utf32_string, scm_from_utf32_stringn,
  scm_to_utf32_string, scm_to_utf32_stringn): New declarations.

* doc/ref/api-data.texi (Conversion to/from C): Document
  `scm_{to,from}_{utf8,utf32}_stringn'.

doc/ref/api-data.texi

@@ -4040,14 +4040,21 @@ conversion functions are provided to convert between Latin-1 C strings
 and Guile strings.
 
 @deftypefn {C Function} SCM scm_from_latin1_stringn (const char *str, size_t len)
-This function returns a scheme string from an ISO-8859-1-encoded C
+@deftypefnx {C Function} SCM scm_from_utf8_stringn (const char *str, size_t len)
-string @var{str} of length @var{len}.
+@deftypefnx {C Function} SCM scm_from_utf32_stringn (const scm_t_wchar *str, size_t len)
+Return a scheme string from C string @var{str}, which is ISO-8859-1-,
+UTF-8-, or UTF-32-encoded, of length @var{len}.  @var{len} is the number
+of bytes pointed to by @var{str} for @code{scm_from_latin1_stringn} and
+@code{scm_from_utf8_stringn}; it is the number of elements (code points)
+in @var{str} in the case of @code{scm_from_utf32_stringn}.
 @end deftypefn
 
-@deftypefn {C function} char * scm_to_latin1_stringn (SCM str, size_t *lenp)
+@deftypefn {C function} char *scm_to_latin1_stringn (SCM str, size_t *lenp)
-This function returns a newly allocated, ISO-8859-1-encoded C string
+@deftypefnx {C function} char *scm_to_utf8_stringn (SCM str, size_t *lenp)
-from the scheme string @var{str}.  An error will be thrown if the scheme
+@deftypefnx {C function} scm_t_wchar *scm_to_utf32_stringn (SCM str, size_t *lenp)
-string cannot be converted to the ISO-8859-1 encoding.  If @var{lenp} is
+Return a newly allocated, ISO-8859-1-, UTF-8-, or UTF-32-encoded C string
+from Scheme string @var{str}.  An error is thrown when @var{str}
+string cannot be converted to the specified encoding.  If @var{lenp} is
 @code{NULL}, the returned C string will be null terminated, and an error
 will be thrown if the C string would otherwise contain null
 characters. If @var{lenp} is not NULL, the length of the string is

libguile/strings.c

@@ -1570,6 +1570,28 @@ scm_from_utf8_stringn (const char *str, size_t len)
   return scm_from_stringn (str, len, "UTF-8", SCM_FAILED_CONVERSION_ERROR);
 }
 
+SCM
+scm_from_utf32_string (const scm_t_wchar *str)
+{
+  return scm_from_utf32_stringn (str, -1);
+}
+
+SCM
+scm_from_utf32_stringn (const scm_t_wchar *str, size_t len)
+{
+  SCM result;
+  scm_t_wchar *buf;
+
+  if (len == (size_t) -1)
+    len = u32_strlen ((uint32_t *) str);
+
+  result = scm_i_make_wide_string (len, &buf);
+  memcpy (buf, str, len * sizeof (scm_t_wchar));
+  scm_i_try_narrow_string (result);
+
+  return result;
+}
+
 /* Create a new scheme string from the C string STR.  The memory of
    STR may be used directly as storage for the new string.  */
 /* FIXME: GC-wise, the only way to use the memory area pointed to by STR
@@ -1795,6 +1817,42 @@ scm_to_utf8_stringn (SCM str, size_t *lenp)
   return scm_to_stringn (str, lenp, "UTF-8", SCM_FAILED_CONVERSION_ERROR);
 }
 
+scm_t_wchar *
+scm_to_utf32_string (SCM str)
+{
+  return scm_to_utf32_stringn (str, NULL);
+}
+
+scm_t_wchar *
+scm_to_utf32_stringn (SCM str, size_t *lenp)
+#define FUNC_NAME "scm_to_utf32_stringn"
+{
+  scm_t_wchar *result;
+
+  SCM_VALIDATE_STRING (1, str);
+
+  if (scm_i_is_narrow_string (str))
+    result = (scm_t_wchar *)
+      scm_to_stringn (str, lenp, "UTF-32",
+		      SCM_FAILED_CONVERSION_ERROR);
+  else
+    {
+      size_t len;
+
+      len = scm_i_string_length (str);
+      if (lenp)
+	*lenp = len;
+
+      result = scm_malloc ((len + 1) * sizeof (scm_t_wchar));
+      memcpy (result, scm_i_string_wide_chars (str),
+	      len * sizeof (scm_t_wchar));
+      result[len] = 0;
+    }
+
+  return result;
+}
+#undef FUNC_NAME
+
 /* Return a malloc(3)-allocated buffer containing the contents of STR encoded
    according to ENCODING.  If LENP is non-NULL, set it to the size in bytes of
    the returned buffer.  If the conversion to ENCODING fails, apply the strategy

libguile/strings.h

@@ -148,6 +148,11 @@ SCM_API char *scm_to_utf8_stringn (SCM str, size_t *lenp);
 SCM_API SCM scm_from_utf8_string (const char *str);
 SCM_API SCM scm_from_utf8_stringn (const char *str, size_t len);
 
+SCM_API scm_t_wchar *scm_to_utf32_string (SCM str);
+SCM_API scm_t_wchar *scm_to_utf32_stringn (SCM str, size_t *lenp);
+SCM_API SCM scm_from_utf32_string (const scm_t_wchar *str);
+SCM_API SCM scm_from_utf32_stringn (const scm_t_wchar *str, size_t len);
+
 SCM_API char *scm_to_stringn (SCM str, size_t *lenp, const char *encoding,
                               scm_t_string_failed_conversion_handler handler);
 SCM_API size_t scm_to_locale_stringbuf (SCM str, char *buf, size_t max_len);