1 files changed, 47 insertions, 0 deletions
diff --git a/stdio/ungetwc.c b/stdio/ungetwc.c
new file mode 100644
index 0000000..be1fce4
--- /dev/null
+++ b/stdio/ungetwc.c
@@ -0,0 +1,47 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=8 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/stdio/stdio.h"
+#include "libc/str/str.h"
+#include "libc/str/tpenc.h"
+
+/**
+ * Pushes wide character back to stream.
+ */
+wint_t ungetwc(wint_t c, FILE *f) {
+  char b[6];
+  unsigned n;
+  uint64_t w;
+  if (c == -1) return -1;
+  n = 0;
+  w = tpenc(c);
+  do {
+    b[n++] = w;
+  } while ((w >>= 8));
+  if (f->beg >= n) {
+    f->beg -= n;
+    memcpy(f->buf + f->beg, b, n);
+  } else if (f->beg + f->end + n <= f->size) {
+    memmove(f->buf + f->beg + n, f->buf + f->beg, f->end - f->beg);
+    memcpy(f->buf + f->beg, b, n);
+    f->end += n;
+  } else {
+    return -1;
+  }
+  return c;
+}