Initial Contribution
diff --git a/libc/stdio/ungetc.c b/libc/stdio/ungetc.c
new file mode 100644
index 0000000..fe05258
--- /dev/null
+++ b/libc/stdio/ungetc.c
@@ -0,0 +1,141 @@
+/* $OpenBSD: ungetc.c,v 1.9 2005/08/08 08:05:36 espie Exp $ */
+/*-
+ * Copyright (c) 1990, 1993
+ * The Regents of the University of California. All rights reserved.
+ *
+ * This code is derived from software contributed to Berkeley by
+ * Chris Torek.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ * may be used to endorse or promote products derived from this software
+ * without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "local.h"
+
+static int __submore(FILE *);
+/*
+ * Expand the ungetc buffer `in place'. That is, adjust fp->_p when
+ * the buffer moves, so that it points the same distance from the end,
+ * and move the bytes in the buffer around as necessary so that they
+ * are all at the end (stack-style).
+ */
+static int
+__submore(FILE *fp)
+{
+ int i;
+ unsigned char *p;
+
+ if (_UB(fp)._base == fp->_ubuf) {
+ /*
+ * Get a new buffer (rather than expanding the old one).
+ */
+ if ((p = malloc((size_t)BUFSIZ)) == NULL)
+ return (EOF);
+ _UB(fp)._base = p;
+ _UB(fp)._size = BUFSIZ;
+ p += BUFSIZ - sizeof(fp->_ubuf);
+ for (i = sizeof(fp->_ubuf); --i >= 0;)
+ p[i] = fp->_ubuf[i];
+ fp->_p = p;
+ return (0);
+ }
+ i = _UB(fp)._size;
+ p = realloc(_UB(fp)._base, i << 1);
+ if (p == NULL)
+ return (EOF);
+ /* no overlap (hence can use memcpy) because we doubled the size */
+ (void)memcpy((void *)(p + i), (void *)p, (size_t)i);
+ fp->_p = p + i;
+ _UB(fp)._base = p;
+ _UB(fp)._size = i << 1;
+ return (0);
+}
+
+int
+ungetc(int c, FILE *fp)
+{
+ if (c == EOF)
+ return (EOF);
+ if (!__sdidinit)
+ __sinit();
+ _SET_ORIENTATION(fp, -1);
+ if ((fp->_flags & __SRD) == 0) {
+ /*
+ * Not already reading: no good unless reading-and-writing.
+ * Otherwise, flush any current write stuff.
+ */
+ if ((fp->_flags & __SRW) == 0)
+ return (EOF);
+ if (fp->_flags & __SWR) {
+ if (__sflush(fp))
+ return (EOF);
+ fp->_flags &= ~__SWR;
+ fp->_w = 0;
+ fp->_lbfsize = 0;
+ }
+ fp->_flags |= __SRD;
+ }
+ c = (unsigned char)c;
+
+ /*
+ * If we are in the middle of ungetc'ing, just continue.
+ * This may require expanding the current ungetc buffer.
+ */
+ if (HASUB(fp)) {
+ if (fp->_r >= _UB(fp)._size && __submore(fp))
+ return (EOF);
+ *--fp->_p = c;
+ fp->_r++;
+ return (c);
+ }
+ fp->_flags &= ~__SEOF;
+
+ /*
+ * If we can handle this by simply backing up, do so,
+ * but never replace the original character.
+ * (This makes sscanf() work when scanning `const' data.)
+ */
+ if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
+ fp->_p[-1] == c) {
+ fp->_p--;
+ fp->_r++;
+ return (c);
+ }
+
+ /*
+ * Create an ungetc buffer.
+ * Initially, we will use the `reserve' buffer.
+ */
+ fp->_ur = fp->_r;
+ fp->_up = fp->_p;
+ _UB(fp)._base = fp->_ubuf;
+ _UB(fp)._size = sizeof(fp->_ubuf);
+ fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
+ fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
+ fp->_r = 1;
+ return (c);
+}