Extract execution engines definitions into their own crates (#4489)

* Clean imports in wasmi_execution

* Replace `interpret_runtime_api_result` with `pointer_and_len_from_u64`.

* Extract sc-executor-common crate

* Extract `sc-executor-wasmi` into its own crate

* Extract `sc-executor-wasmtime` into its own crate.

* Add missing headers.

* Clean and docs

* Docs for sc-executor-wasmi

* Expand a comment about sandboxing

* Fix assert_matches

* Rename (un)pack_ptr_and_len and move them into util module

* Remove wasmtime errors in sc-executor-common

substrate/primitives/runtime-interface/src/util.rs

@@ -0,0 +1,59 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate 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 of the License, or
+// (at your option) any later version.
+
+// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Various utilities that help interfacing with wasm runtime code.
+
+/// Pack a pointer and length into an `u64`.
+pub fn pack_ptr_and_len(ptr: u32, len: u32) -> u64 {
+	// The static assertions from above are changed into a runtime check.
+	#[cfg(all(not(feature = "std"), feature = "disable_target_static_assertions"))]
+	assert_eq!(4, sp_std::mem::size_of::<usize>());
+
+	(u64::from(len) << 32) | u64::from(ptr)
+}
+
+/// Unpacks an `u64` into the pointer and length.
+///
+/// Runtime API functions return a 64-bit value which encodes a pointer in the least-significant
+/// 32-bits and a length in the most-significant 32 bits. This interprets the returned value as a pointer,
+/// length tuple.
+pub fn unpack_ptr_and_len(val: u64) -> (u32, u32) {
+	// The static assertions from above are changed into a runtime check.
+	#[cfg(all(not(feature = "std"), feature = "disable_target_static_assertions"))]
+	assert_eq!(4, sp_std::mem::size_of::<usize>());
+
+	let ptr = (val & (!0u32 as u64)) as u32;
+	let len = (val >> 32) as u32;
+
+	(ptr, len)
+}
+
+#[cfg(test)]
+mod tests {
+	use super::{pack_ptr_and_len, unpack_ptr_and_len};
+
+	#[test]
+	fn ptr_len_packing_unpacking() {
+		const PTR: u32 = 0x1337;
+		const LEN: u32 = 0x7f000000;
+
+		let packed = pack_ptr_and_len(PTR, LEN);
+		let (ptr, len) = unpack_ptr_and_len(packed);
+
+		assert_eq!(PTR, ptr);
+		assert_eq!(LEN, len);
+	}
+}