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char: replace comparison with bit checks in utf8len()

--- a/char.c

+++ b/char.c

@@ -7,19 +7,19 @@

 /* return the length of a utf-8 character based on its first byte */

 int utf8len(int c)

 {

-	if (c > 0 && c <= 0x7f)

-		return 1;

-	if (c >= 0xfc)

-		return 6;

-	if (c >= 0xf8)

-		return 5;

-	if (c >= 0xf0)

-		return 4;

-	if (c >= 0xe0)

-		return 3;

-	if (c >= 0xc0)

+	if (~c & 0x80)

+		return c > 0;

+	if (~c & 0x20)

 		return 2;

-	return c != 0;

+	if (~c & 0x10)

+		return 3;

+	if (~c & 0x80)

+		return 4;

+	if (~c & 0x40)

+		return 5;

+	if (~c & 0x20)

+		return 6;

+	return 1;

 }

 /* return nonzero if s is a single utf-8 character */