Merge #747

747: Base v0 mangling grammar r=philberty a=CohenArthur

This PR adds base functions to deal with the v0 mangling grammar, [found here](https://rust-lang.github.io/rfcs/2603-rust-symbol-name-mangling-v0.html#syntax-of-mangled-names).

I have a few questions regarding this implementation:
1/ Is there any existing implementation for the base62 algorithm used here? This is directly adapted from [rustc's base_n module](https://github.com/rust-lang/rust/blob/6f53ddfa74ac3c10ceb63ad4a7a9c95e55853c87/compiler/rustc_data_structures/src/base_n.rs#L16) which I'm assuming is relatively standard and might already exist in the compiler. I haven't been able to find it however.
2/ gccrs cannot yet deal with unicode identifiers, as pointed out by `@bjorn3` in #418. This means that a big chunk of the `v0_add_identifier` implementation is missing. Should it be added in this PR too?
3/ As mentionned in zulip, it would be great to be able to create unit tests for this piece of code. It would be quite easy to generate a bunch of base62 strings and ensure that the algorithm here matches with them.

Co-authored-by: CohenArthur <arthur.cohen@epita.fr>

1 files changed, 48 insertions, 0 deletions

diff --git a/gcc/rust/util/rust-base62.cc b/gcc/rust/util/rust-base62.cc
new file mode 100644
index 0000000..f1e3202
--- /dev/null
+++ b/gcc/rust/util/rust-base62.cc
@@ -0,0 +1,48 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+
+// This file is part of GCC.
+
+// GCC is free software; you can redistribute it and/or modify it under
+// the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3, or (at your option) any later
+// version.
+
+// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+// WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+// for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with GCC; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include "rust-base62.h"
+
+#include <algorithm>
+
+namespace Rust {
+
+std::string
+base62_integer (uint64_t value)
+{
+  const static std::string base_64
+    = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ@$";
+  std::string buffer (128, '\0');
+  size_t idx = 0;
+  size_t base = 62;
+
+  do
+    {
+      buffer[idx] = base_64[(value % base)];
+      idx++;
+      value = value / base;
+    }
+  while (value != 0);
+
+  std::reverse (buffer.begin (), buffer.begin () + idx);
+  return buffer.substr (0, idx);
+}
+
+} // namespace Rust
+
+// FIXME: Add unit testing using the selftest framework