Fix folder names in primitives (#4358)

* sr-arithmetic -> arithmetic

* sr-sandbox -> sandbox

* primitives/sr-staking-primitives -> primitives/staking

* primitives/sr-version -> primitives/version

* primitives/block-builder/runtime-api -> primitives/block-builder

substrate/primitives/arithmetic/fuzzer/src/rational128.rs

@@ -0,0 +1,77 @@
+// 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/>.
+
+//! # Running
+//! Running this fuzzer can be done with `cargo hfuzz run rational128`. `honggfuzz` CLI options can
+//! be used by setting `HFUZZ_RUN_ARGS`, such as `-n 4` to use 4 threads.
+//!
+//! # Debugging a panic
+//! Once a panic is found, it can be debugged with
+//! `cargo hfuzz run-debug rational128 hfuzz_workspace/rational128/*.fuzz`.
+//!
+//! # More infomation
+//! More information about `honggfuzz` can be found
+//! [here](https://docs.rs/honggfuzz/).
+
+use honggfuzz::fuzz;
+use sp_arithmetic::{helpers_128bit::multiply_by_rational, traits::Zero};
+
+fn main() {
+	loop {
+		fuzz!(|data: ([u8; 16], [u8; 16], [u8; 16])| {
+			let (a_bytes, b_bytes, c_bytes) = data;
+			let (a, b, c) = (
+				u128::from_be_bytes(a_bytes),
+				u128::from_be_bytes(b_bytes),
+				u128::from_be_bytes(c_bytes),
+			);
+
+			println!("++ Equation: {} * {} / {}", a, b, c);
+
+			// The point of this fuzzing is to make sure that `multiply_by_rational` is 100%
+			// accurate as long as the value fits in a u128.
+			if let Ok(result) = multiply_by_rational(a, b, c) {
+				let truth = mul_div(a, b, c);
+
+				if result != truth && result != truth + 1 {
+					println!("++ Expected {}", truth);
+					println!("+++++++ Got {}", result);
+					panic!();
+				}
+			}
+		})
+	}
+}
+
+fn mul_div(a: u128, b: u128, c: u128) -> u128 {
+	use primitive_types::U256;
+	if a.is_zero() {
+		return Zero::zero();
+	}
+	let c = c.max(1);
+
+	// e for extended
+	let ae: U256 = a.into();
+	let be: U256 = b.into();
+	let ce: U256 = c.into();
+
+	let r = ae * be / ce;
+	if r > u128::max_value().into() {
+		a
+	} else {
+		r.as_u128()
+	}
+}