1 files changed, 77 insertions, 0 deletions
diff --git a/libc/stdio/ungetc.c b/libc/stdio/ungetc.c
new file mode 100644
index 000000000..1b9197a18
--- /dev/null
+++ b/libc/stdio/ungetc.c
@@ -0,0 +1,77 @@
+/* Copyright (C) 2004       Manuel Novoa III    <mjn3@codepoet.org>
+ *
+ * GNU Library General Public License (LGPL) version 2 or later.
+ *
+ * Dedicated to Toni.  See uClibc/DEDICATION.mjn3 for details.
+ */
+
+#include "_stdio.h"
+
+/* Having ungotten characters implies the stream is reading.
+ * The scheme used here treats the least significant 2 bits of
+ * the stream's modeflags member as follows:
+ *   0 0   Not currently reading.
+ *   0 1   Reading, but no ungetc() or scanf() push back chars.
+ *   1 0   Reading with one ungetc() char (ungot[1] is 1)
+ *         or one scanf() pushed back char (ungot[1] is 0).
+ *   1 1   Reading with both an ungetc() char and a scanf()
+ *         pushed back char.  Note that this must be the result
+ *         of a scanf() push back (in ungot[0]) _followed_ by
+ *         an ungetc() call (in ungot[1]).
+ *
+ * Notes:
+ *   scanf() can NOT use ungetc() to push back characters.
+ *     (See section 7.19.6.2 of the C9X rationale -- WG14/N897.)
+ */
+
+int ungetc(int c, register FILE *stream)
+{
+	__STDIO_AUTO_THREADLOCK_VAR;
+
+	__STDIO_AUTO_THREADLOCK(stream);
+	__STDIO_STREAM_VALIDATE(stream);
+
+#ifdef __UCLIBC_MJN3_ONLY__
+#warning CONSIDER: Make fast ungetc an option?
+#endif
+#ifdef __UCLIBC_HAS_STDIO_GETC_MACRO__
+	/* If buffered narrow reading with no ungot slots filled, and if not
+	 * ungetting a different char than the one last read from the buffer,
+	 * we can simply decrement the position and not worry about disabling
+	 * the getc macros.  This will cut down on overhead in applications
+	 * that use getc/ungetc extensively (like gcc). */
+	/* NOTE: If we can use getc, then we are buffered narrow reading with
+	 * no ungot slots filled. */
+	if (__STDIO_STREAM_CAN_USE_BUFFER_GET(stream)
+		&& (c != EOF)
+		&& (stream->__bufpos > stream->__bufstart)
+		&& (stream->__bufpos[-1] == ((unsigned char)c))
+		) {
+		--stream->__bufpos;
+		__STDIO_STREAM_CLEAR_EOF(stream); /* Must clear end-of-file flag. */
+	} else
+#endif
+	/* Note: Even if c == EOF, we need to initialize/verify the
+	 * stream's orientation and ensure the stream is in reading
+	 * mode (if readable and properly oriented). */
+	if ((!__STDIO_STREAM_IS_NARROW_READING(stream)
+		 && __STDIO_STREAM_TRANS_TO_READ(stream, __FLAG_NARROW))
+		|| ((stream->__modeflags & __FLAG_UNGOT)
+			&& ((stream->__modeflags & 1) || stream->__ungot[1]))
+		) {
+		c = EOF;
+	} else if (c != EOF) {
+		__STDIO_STREAM_DISABLE_GETC(stream);
+
+		/* Flag this as a user ungot, as scanf does the necessary fixup. */
+		stream->__ungot[1] = 1;
+		stream->__ungot[(++stream->__modeflags) & 1] = c;
+
+		__STDIO_STREAM_CLEAR_EOF(stream); /* Must clear end-of-file flag. */
+	}
+
+	__STDIO_STREAM_VALIDATE(stream);
+	__STDIO_AUTO_THREADUNLOCK(stream);
+
+	return c;
+}