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+.Dd January 18 2024
+.Dt U8TOR 3
+.Os
+.Sh NAME
+.Nm u8tor ,
+.Nm u8tor_uc
+.Nd decode UTF-8 into a rune
+.Sh LIBRARY
+.Lb librune
+.Sh SYNOPSIS
+.In utf8.h
+.Ft int
+.Fn u8tor "rune *ch" "const char8_t *s"
+.Ft int
+.Fn u8tor_uc "rune *ch" "const char8_t *s"
+.Sh DESCRIPTION
+The
+.Fn u8tor
+and
+.Fn u8tor_uc
+functions decode the first rune in the UTF-8 buffer
+.Fa s ,
+storing the result in the rune pointed to by
+.Fa ch .
+Both functions return the number of bytes which compose the decoded
+UTF-8.
+.Pp
+The two functions are nearly identical,
+however
+.Fn u8tor_uc
+performs fewer range checks than
+.Fn u8tor
+allowing it to process data more efficiently.
+When provided with invalid UTF-8 however,
+.Fn u8tor_uc
+engages in undefined-behavior.
+The
+.Fn u8tor
+function on the other hand handles invalid UTF-8 by storing
+.Dv RUNE_ERROR
+in
+.Fa ch
+and returning 1.
+.Sh RETURN VALUES
+The
+.Fn u8tor
+and
+.Fn u8tor_uc
+functions return the number of bytes from
+.Fa s
+decoded into
+.Fa ch .
+.Pp
+The
+.Fn u8tor
+function returns 1 on invalid UTF-8.
+.Sh EXAMPLES
+The following call to
+.Fn u8tor
+attempts to decode the first UTF-8 codepoint in
+.Va buf .
+.Bd -literal -offset indent
+/* Implementation of read_codepoint() omitted */
+
+int w;
+rune ch;
+char8_t *buf = read_codepoint(stdin);
+
+w = u8tor(&ch, buf);
+if (ch == RUNE_ERROR) {
+	fputs("Got invalid UTF-8 codepoint", stderr);
+	exit(EXIT_FAILURE);
+}
+printf("Got rune ‘%.*s’\en", w, buf);
+.Ed
+.Sh SEE ALSO
+.Xr rtou8 3 ,
+.Xr u8chk 3 ,
+.Xr u8next 3 ,
+.Xr unicode 7 ,
+.Xr utf\-8 7
+.Sh STANDARDS
+.Rs
+.%A F. Yergeau
+.%D November 2003
+.%R RFC 3629
+.%T UTF-8, a transformation format of ISO 10646
+.Re
+.Sh AUTHORS
+.An Thomas Voss Aq Mt mail@thomasvoss.com