[PATCH v4 2/3] libcpp: add a function to determine UTF-8 validity of a C string

[Ben Boeckel <ben.boeckel@kitware.com>]

This simplifies the interface for other UTF-8 validity detections when a
simple "yes" or "no" answer is sufficient.

libcpp/

	* charset.cc: Add `_cpp_valid_utf8_str` which determines whether
	a C string is valid UTF-8 or not.
	* internal.h: Add prototype for `_cpp_valid_utf8_str`.

Signed-off-by: Ben Boeckel <ben.boeckel@kitware.com>
---
 libcpp/charset.cc | 20 ++++++++++++++++++++
 libcpp/internal.h |  2 ++
 2 files changed, 22 insertions(+)

diff --git a/libcpp/charset.cc b/libcpp/charset.cc
index 324b5b19136..422cb52595c 100644
--- a/libcpp/charset.cc
+++ b/libcpp/charset.cc
@@ -1868,6 +1868,26 @@ _cpp_valid_utf8 (cpp_reader *pfile,
   return true;
 }
 
+/*  Detect whether a C-string is a valid UTF-8-encoded set of bytes. Returns
+    `false` if any contained byte sequence encodes an invalid Unicode codepoint
+    or is not a valid UTF-8 sequence. Returns `true` otherwise. */
+
+extern bool
+_cpp_valid_utf8_str (const char *name)
+{
+  const uchar* in = (const uchar*)name;
+  size_t len = strlen (name);
+  cppchar_t cp;
+
+  while (*in)
+    {
+      if (one_utf8_to_cppchar (&in, &len, &cp))
+	return false;
+    }
+
+  return true;
+}
+
 /* Subroutine of convert_hex and convert_oct.  N is the representation
    in the execution character set of a numeric escape; write it into the
    string buffer TBUF and update the end-of-string pointer therein.  WIDE
diff --git a/libcpp/internal.h b/libcpp/internal.h
index badfd1b40da..4f2dd4a2f5c 100644
--- a/libcpp/internal.h
+++ b/libcpp/internal.h
@@ -834,6 +834,8 @@ extern bool _cpp_valid_utf8 (cpp_reader *pfile,
 			     struct normalize_state *nst,
 			     cppchar_t *cp);
 
+extern bool _cpp_valid_utf8_str (const char *str);
+
 extern void _cpp_destroy_iconv (cpp_reader *);
 extern unsigned char *_cpp_convert_input (cpp_reader *, const char *,
 					  unsigned char *, size_t, size_t,
-- 
2.38.1