Rearrange sources (#4997)

include/xrpl/basics/mulDiv.h

@@ -0,0 +1,46 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of rippled: https://github.com/ripple/rippled
+    Copyright (c) 2012-2015 Ripple Labs Inc.
+
+    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.
+*/
+//==============================================================================
+
+#ifndef RIPPLE_BASICS_MULDIV_H_INCLUDED
+#define RIPPLE_BASICS_MULDIV_H_INCLUDED
+
+#include <cstdint>
+#include <limits>
+#include <optional>
+#include <utility>
+
+namespace ripple {
+auto constexpr muldiv_max = std::numeric_limits<std::uint64_t>::max();
+
+/** Return value*mul/div accurately.
+    Computes the result of the multiplication and division in
+    a single step, avoiding overflow and retaining precision.
+    Throws:
+        None
+    Returns:
+        `std::optional`:
+            `std::nullopt` if the calculation overflows. Otherwise, `value * mul
+   / div`.
+*/
+std::optional<std::uint64_t>
+mulDiv(std::uint64_t value, std::uint64_t mul, std::uint64_t div);
+
+}  // namespace ripple
+
+#endif