vt: rearrange vc_translate_unicode

The code was too overcomplicated. Extract vc_sanitize_unicode to a
separate function and flatten the code. I believe the code is
straightforward now.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20200615074910.19267-13-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index caaad82..5004242 100644 (file)
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -2572,6 +2572,19 @@ static inline int vc_translate_ascii(const struct vc_data *vc, int c)
        return c;
 }
 
+
+/**
+ * vc_sanitize_unicode -- Replace invalid Unicode code points with U+FFFD
+ * @c: the received character, or U+FFFD for invalid sequences.
+ */
+static inline int vc_sanitize_unicode(const int c)
+{
+       if ((c >= 0xd800 && c <= 0xdfff) || c == 0xfffe || c == 0xffff)
+               return 0xfffd;
+
+       return c;
+}
+
 /**
  * vc_translate_unicode -- Combine UTF-8 into Unicode in @vc_utf_char
  *
@@ -2586,69 +2599,63 @@ static int vc_translate_unicode(struct vc_data *vc, int c, bool *rescan)
                0x001fffff, 0x03ffffff, 0x7fffffff
        };
 
+       /* Continuation byte received */
        if ((c & 0xc0) == 0x80) {
-               /* Continuation byte received */
-               if (vc->vc_utf_count) {
-                       vc->vc_utf_char = (vc->vc_utf_char << 6) | (c & 0x3f);
-                       vc->vc_npar++;
-                       if (--vc->vc_utf_count) {
-                               /* Still need some bytes */
-                               return -1;
-                       }
-                       /* Got a whole character */
-                       c = vc->vc_utf_char;
-                       /* Reject overlong sequences */
-                       if (c <= utf8_length_changes[vc->vc_npar - 1] ||
-                                       c > utf8_length_changes[vc->vc_npar])
-                               return 0xfffd;
-               } else {
-                       /* Unexpected continuation byte */
-                       vc->vc_utf_count = 0;
+               /* Unexpected continuation byte? */
+               if (!vc->vc_utf_count)
                        return 0xfffd;
-               }
-       } else {
-               /* Single ASCII byte or first byte of a sequence received */
-               if (vc->vc_utf_count) {
-                       /* Continuation byte expected */
-                       *rescan = true;
-                       vc->vc_utf_count = 0;
+
+               vc->vc_utf_char = (vc->vc_utf_char << 6) | (c & 0x3f);
+               vc->vc_npar++;
+               if (--vc->vc_utf_count)
+                       goto need_more_bytes;
+
+               /* Got a whole character */
+               c = vc->vc_utf_char;
+               /* Reject overlong sequences */
+               if (c <= utf8_length_changes[vc->vc_npar - 1] ||
+                               c > utf8_length_changes[vc->vc_npar])
                        return 0xfffd;
-               } else if (c > 0x7f) {
-                       /* First byte of a multibyte sequence received */
-                       vc->vc_npar = 0;
-                       if ((c & 0xe0) == 0xc0) {
-                               vc->vc_utf_count = 1;
-                               vc->vc_utf_char = (c & 0x1f);
-                       } else if ((c & 0xf0) == 0xe0) {
-                               vc->vc_utf_count = 2;
-                               vc->vc_utf_char = (c & 0x0f);
-                       } else if ((c & 0xf8) == 0xf0) {
-                               vc->vc_utf_count = 3;
-                               vc->vc_utf_char = (c & 0x07);
-                       } else if ((c & 0xfc) == 0xf8) {
-                               vc->vc_utf_count = 4;
-                               vc->vc_utf_char = (c & 0x03);
-                       } else if ((c & 0xfe) == 0xfc) {
-                               vc->vc_utf_count = 5;
-                               vc->vc_utf_char = (c & 0x01);
-                       } else {
-                               /* 254 and 255 are invalid */
-                               return 0xfffd;
-                       }
-                       if (vc->vc_utf_count) {
-                               /* Still need some bytes */
-                               return -1;
-                       }
-               }
-               /* Nothing to do if an ASCII byte was received */
+
+               return vc_sanitize_unicode(c);
        }
-       /* End of UTF-8 decoding. */
-       /* c is the received character, or U+FFFD for invalid sequences. */
-       /* Replace invalid Unicode code points with U+FFFD too */
-       if ((c >= 0xd800 && c <= 0xdfff) || c == 0xfffe || c == 0xffff)
+
+       /* Single ASCII byte or first byte of a sequence received */
+       if (vc->vc_utf_count) {
+               /* Continuation byte expected */
+               *rescan = true;
+               vc->vc_utf_count = 0;
                return 0xfffd;
+       }
 
-       return c;
+       /* Nothing to do if an ASCII byte was received */
+       if (c <= 0x7f)
+               return c;
+
+       /* First byte of a multibyte sequence received */
+       vc->vc_npar = 0;
+       if ((c & 0xe0) == 0xc0) {
+               vc->vc_utf_count = 1;
+               vc->vc_utf_char = (c & 0x1f);
+       } else if ((c & 0xf0) == 0xe0) {
+               vc->vc_utf_count = 2;
+               vc->vc_utf_char = (c & 0x0f);
+       } else if ((c & 0xf8) == 0xf0) {
+               vc->vc_utf_count = 3;
+               vc->vc_utf_char = (c & 0x07);
+       } else if ((c & 0xfc) == 0xf8) {
+               vc->vc_utf_count = 4;
+               vc->vc_utf_char = (c & 0x03);
+       } else if ((c & 0xfe) == 0xfc) {
+               vc->vc_utf_count = 5;
+               vc->vc_utf_char = (c & 0x01);
+       } else {
+               /* 254 and 255 are invalid */
+               return 0xfffd;
+       }
+
+need_more_bytes:
+       return -1;
 }
 
 /* acquires console_lock */