[libc-commits] [libc] [libc] Add getc, ungetc, fflush to enable libc++ iostream on baremetal (PR #175530)

[Volodymyr Turanskyy via libc-commits]

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@@ -0,0 +1,54 @@
+//===--- Helpers for file I/O on baremetal ----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdio/baremetal/file_internal.h"
+
+#include "hdr/stdio_macros.h" // for EOF
+
+namespace LIBC_NAMESPACE_DECL {
+
+// Baremetal only exposes three fixed streams now and only stdin supports ungetc
+// because stdin is readable - ungetc on stdout/stderr is undefined.
+// Only one value is required by the C standard to be stored by ungetc.
+extern "C" ::FILE *stdin;
+
+struct UngetcState {
+  bool has_value;
+  unsigned char value;
+};
+
+static UngetcState ungetc_state_stdin{false, 0};
+
+bool pop_ungetc_value(::FILE *stream, unsigned char &out) {
+  if (stream != stdin)
+    return false;
+
+  if (ungetc_state_stdin.has_value) {
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voltur01 wrote:

Agreed, tried to rearrange.

https://github.com/llvm/llvm-project/pull/175530