Use sensible maths for from_rational (#13660)

* Use sensible maths for from_rational * Fixes * Fixes * More fixes * Remove debugging * Add fuzzer tests Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * Prevent panics Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * docs Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * Clean up old code Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * Test all rounding modes of from_rational Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * Clean up code Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * Revert "Prevent panics" This reverts commit 7e88ac76138a1b590e68b68318505b69efe1e1f6. * fix imports Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * cleanup Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * Fuzz test multiply_rational Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * Fix import Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * fmt Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * Return None in multiply_rational on zero div Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> --------- Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
2026-04-27 03:27:58 +00:00 · 2023-03-24 14:48:37 +00:00
parent 40e1704e1c
commit 2c77f8f4ca
12 changed files with 372 additions and 227 deletions
@@ -0,0 +1,69 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! # Running
+//! Running this fuzzer can be done with `cargo hfuzz run per_thing_mult_fraction`. `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 per_thing_mult_fraction hfuzz_workspace/per_thing_mult_fraction/*.fuzz`.
+
+use honggfuzz::fuzz;
+use sp_arithmetic::{PerThing, Perbill, Percent, Perquintill, *};
+
+/// Tries to disprove `(n / d) * d <= n` for any `PerThing`s.
+fn main() {
+	loop {
+		fuzz!(|data: (u128, u128)| {
+			let (n, d) = (data.0.min(data.1), data.0.max(data.1).max(1));
+
+			check_mul::<PerU16>(n, d);
+			check_mul::<Percent>(n, d);
+			check_mul::<Perbill>(n, d);
+			check_mul::<Perquintill>(n, d);
+
+			check_reciprocal_mul::<PerU16>(n, d);
+			check_reciprocal_mul::<Percent>(n, d);
+			check_reciprocal_mul::<Perbill>(n, d);
+			check_reciprocal_mul::<Perquintill>(n, d);
+		})
+	}
+}
+
+/// Checks that `(n / d) * d <= n`.
+fn check_mul<P: PerThing>(n: u128, d: u128)
+where
+	P: PerThing + core::ops::Mul<u128, Output = u128>,
+{
+	let q = P::from_rational_with_rounding(n, d, Rounding::Down).unwrap();
+	assert!(q * d <= n, "{:?} * {:?} <= {:?}", q, d, n);
+}
+
+/// Checks that `n / (n / d) >= d`.
+fn check_reciprocal_mul<P: PerThing>(n: u128, d: u128)
+where
+	P: PerThing + core::ops::Mul<u128, Output = u128>,
+{
+	let q = P::from_rational_with_rounding(n, d, Rounding::Down).unwrap();
+	if q.is_zero() {
+		return
+	}
+
+	let r = q.saturating_reciprocal_mul_floor(n);
+	assert!(r >= d, "{} / ({} / {}) != {} but {}", n, n, d, d, r);
+}