[gcc r13-4653] gccrs: Add Base62 implementation

[Arthur Cohen <cohenarthur@gcc.gnu.org>]

https://gcc.gnu.org/g:eb10bc5225e03c32175b32c4778e937e64f7ddaa

commit r13-4653-geb10bc5225e03c32175b32c4778e937e64f7ddaa
Author: Arthur Cohen <arthur.cohen@embecosm.com>
Date:   Tue Aug 23 16:26:01 2022 +0100

    gccrs: Add Base62 implementation
    
    Used for V0 symbol mangling scheme which is still in development.
    
            gcc/rust/
            * util/rust-base62.cc: New.
            * util/rust-base62.h: New.

Diff:
---
 gcc/rust/util/rust-base62.cc | 46 ++++++++++++++++++++++++++++++++++++++++++++
 gcc/rust/util/rust-base62.h  | 34 ++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)

diff --git a/gcc/rust/util/rust-base62.cc b/gcc/rust/util/rust-base62.cc
new file mode 100644
index 00000000000..bdab23338c3
--- /dev/null
+++ b/gcc/rust/util/rust-base62.cc
@@ -0,0 +1,46 @@
+// Copyright (C) 2020-2022 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"
+
+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
diff --git a/gcc/rust/util/rust-base62.h b/gcc/rust/util/rust-base62.h
new file mode 100644
index 00000000000..fa610d3e5a4
--- /dev/null
+++ b/gcc/rust/util/rust-base62.h
@@ -0,0 +1,34 @@
+// Copyright (C) 2020-2022 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/>.
+
+#ifndef RUST_BASE62_H
+#define RUST_BASE62_H
+
+#include "rust-system.h"
+
+namespace Rust {
+
+/**
+ * Get the Base62 representation of an integer
+ */
+std::string
+base62_integer (uint64_t value);
+
+} // namespace Rust
+
+#endif /* !RUST_BASE62_H */