Support arbitrary::Arbitrary

num-bigint already supports quickcheck::Arbitrary which works roughly
like arbitrary::Arbitrary. arbitrary::Arbitrary used by cargo-fuzz and
makes it easier to use num-bigint BigInt and BigUint in projects that
want to fuzz that way.

Author: e00E

Cargo.toml

@@ -15,7 +15,7 @@ exclude = ["/bors.toml", "/ci/*", "/.github/*"]
 edition = "2018"
 
 [package.metadata.docs.rs]
-features = ["std", "serde", "rand", "quickcheck"]
+features = ["std", "serde", "rand", "quickcheck", "arbitrary"]
 
 [[bench]]
 name = "bigint"
@@ -60,6 +60,11 @@ optional = true
 version = "0.9"
 default-features = false
 
+[dependencies.arbitrary]
+optional = true
+version = "0.4"
+default-features = false
+
 [features]
 default = ["std"]
 std = ["num-integer/std", "num-traits/std"]

fuzz/.gitignore

@@ -0,0 +1,3 @@
+target
+corpus
+artifacts

fuzz/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "num-bigint-fuzz"
+version = "0.0.0"
+authors = ["Automatically generated"]
+publish = false
+edition = "2018"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.3"
+
+[dependencies.num-bigint]
+path = ".."
+features = ["arbitrary"]
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[[bin]]
+name = "fuzz_target_1"
+path = "fuzz_targets/fuzz_target_1.rs"
+test = false
+doc = false

fuzz/fuzz_targets/fuzz_target_1.rs

@@ -0,0 +1,7 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+use num_bigint::BigUint;
+
+fuzz_target!(|a: BigUint| {
+    assert_eq!((&a * &a).sqrt(), a);
+});

src/bigint.rs

@@ -1,7 +1,7 @@
 // `Add`/`Sub` ops may flip from `BigInt` to its `BigUint` magnitude
 #![allow(clippy::suspicious_arithmetic_impl)]
 
-#[cfg(feature = "quickcheck")]
+#[cfg(any(feature = "quickcheck", feature = "arbitrary"))]
 use crate::std_alloc::Box;
 use crate::std_alloc::{String, Vec};
 use core::cmp::Ordering::{self, Equal, Greater, Less};
@@ -39,9 +39,6 @@ use crate::TryFromBigIntError;
 use crate::IsizePromotion;
 use crate::UsizePromotion;
 
-#[cfg(feature = "quickcheck")]
-use quickcheck::{Arbitrary, Gen};
-
 /// A Sign is a `BigInt`'s composing element.
 #[derive(PartialEq, PartialOrd, Eq, Ord, Copy, Clone, Debug, Hash)]
 pub enum Sign {
@@ -141,8 +138,8 @@ impl Clone for BigInt {
 }
 
 #[cfg(feature = "quickcheck")]
-impl Arbitrary for BigInt {
-    fn arbitrary<G: Gen>(g: &mut G) -> Self {
+impl quickcheck::Arbitrary for BigInt {
+    fn arbitrary<G: quickcheck::Gen>(g: &mut G) -> Self {
         let positive = bool::arbitrary(g);
         let sign = if positive { Sign::Plus } else { Sign::Minus };
         Self::from_biguint(sign, BigUint::arbitrary(g))
@@ -155,6 +152,26 @@ impl Arbitrary for BigInt {
     }
 }
 
+#[cfg(feature = "arbitrary")]
+mod abitrary_impl {
+    use super::*;
+    use arbitrary::{Arbitrary, Result, Unstructured};
+
+    impl Arbitrary for BigInt {
+        fn arbitrary(u: &mut Unstructured<'_>) -> Result<Self> {
+            let positive = bool::arbitrary(u)?;
+            let sign = if positive { Sign::Plus } else { Sign::Minus };
+            Ok(Self::from_biguint(sign, BigUint::arbitrary(u)?))
+        }
+
+        fn shrink(&self) -> Box<dyn Iterator<Item = Self>> {
+            let sign = self.sign();
+            let unsigned_shrink = self.data.shrink();
+            Box::new(unsigned_shrink.map(move |x| BigInt::from_biguint(sign, x)))
+        }
+    }
+}
+
 impl hash::Hash for BigInt {
     #[inline]
     fn hash<H: hash::Hasher>(&self, state: &mut H) {

src/biguint.rs

@@ -1,4 +1,4 @@
-#[cfg(feature = "quickcheck")]
+#[cfg(any(feature = "quickcheck", feature = "arbitrary"))]
 use crate::std_alloc::Box;
 use crate::std_alloc::{Cow, String, Vec};
 use core::cmp;
@@ -45,9 +45,6 @@ use crate::ParseBigIntError;
 #[cfg(has_try_from)]
 use crate::TryFromBigIntError;
 
-#[cfg(feature = "quickcheck")]
-use quickcheck::{Arbitrary, Gen};
-
 /// A big unsigned integer type.
 #[derive(Debug)]
 pub struct BigUint {
@@ -71,8 +68,8 @@ impl Clone for BigUint {
 }
 
 #[cfg(feature = "quickcheck")]
-impl Arbitrary for BigUint {
-    fn arbitrary<G: Gen>(g: &mut G) -> Self {
+impl quickcheck::Arbitrary for BigUint {
+    fn arbitrary<G: quickcheck::Gen>(g: &mut G) -> Self {
         // Use arbitrary from Vec
         biguint_from_vec(Vec::<BigDigit>::arbitrary(g))
     }
@@ -83,6 +80,22 @@ impl Arbitrary for BigUint {
     }
 }
 
+#[cfg(feature = "arbitrary")]
+mod abitrary_impl {
+    use super::*;
+    use arbitrary::{Arbitrary, Result, Unstructured};
+
+    impl Arbitrary for BigUint {
+        fn arbitrary(u: &mut Unstructured<'_>) -> Result<Self> {
+            Ok(biguint_from_vec(Vec::<BigDigit>::arbitrary(u)?))
+        }
+
+        fn shrink(&self) -> Box<dyn Iterator<Item = Self>> {
+            Box::new(self.data.shrink().map(biguint_from_vec))
+        }
+    }
+}
+
 impl hash::Hash for BigUint {
     #[inline]
     fn hash<H: hash::Hasher>(&self, state: &mut H) {

src/lib.rs

@@ -94,7 +94,7 @@ extern crate std;
 #[cfg(feature = "std")]
 mod std_alloc {
     pub(crate) use std::borrow::Cow;
-    #[cfg(feature = "quickcheck")]
+    #[cfg(any(feature = "quickcheck", feature = "arbitrary"))]
     pub(crate) use std::boxed::Box;
     pub(crate) use std::string::String;
     pub(crate) use std::vec::Vec;
@@ -107,7 +107,7 @@ extern crate alloc;
 #[cfg(not(feature = "std"))]
 mod std_alloc {
     pub(crate) use alloc::borrow::Cow;
-    #[cfg(feature = "quickcheck")]
+    #[cfg(any(feature = "quickcheck", feature = "arbitrary"))]
     pub(crate) use alloc::boxed::Box;
     pub(crate) use alloc::string::String;
     pub(crate) use alloc::vec::Vec;