feat: add arbitrary support

adds arbitrary support to BigInt and BigUint

Cargo.toml

@@ -21,7 +21,9 @@ autobenches = false
 [package.metadata.docs.rs]
 features = ["std", "serde", "rand", "prime"]
 
-[dependencies]
+[dependencies.arbitrary]
+version = "1.1.0"
+optional = true
 
 [dependencies.smallvec]
 version = "1.0.0"
@@ -82,6 +84,7 @@ version = "1.0"
 
 [features]
 default = ["std", "u64_digit"]
+fuzz = ["arbitrary", "smallvec/arbitrary"]
 i128 = []
 std = [
     "num-integer/std",

src/algorithms/div.rs

@@ -1,6 +1,6 @@
+use core::cmp::Ordering;
 use num_traits::{One, Zero};
 use smallvec::SmallVec;
-use core::cmp::Ordering;
 
 use crate::algorithms::{add2, cmp_slice, sub2};
 use crate::big_digit::{self, BigDigit, DoubleBigDigit};

src/algorithms/gcd.rs

@@ -3,9 +3,9 @@ use crate::bigint::Sign::*;
 use crate::bigint::{BigInt, ToBigInt};
 use crate::biguint::{BigUint, IntDigits};
 use crate::integer::Integer;
-use num_traits::{One, Signed, Zero};
 use alloc::borrow::Cow;
 use core::ops::Neg;
+use num_traits::{One, Signed, Zero};
 
 /// XGCD sets z to the greatest common divisor of a and b and returns z.
 /// If extended is true, XGCD returns their value such that z = a*x + b*y.

src/algorithms/jacobi.rs

@@ -97,5 +97,4 @@ mod tests {
             assert_eq!(case[2] as isize, jacobi(&x, &y), "jacobi({}, {})", x, y);
         }
     }
-
 }

src/bigint.rs

@@ -3311,6 +3311,24 @@ impl<'a, 'b> ExtendedGcd<&'b BigUint> for &'a BigInt {
     }
 }
 
+// arbitrary support
+#[cfg(feature = "fuzz")]
+impl arbitrary::Arbitrary<'_> for BigInt {
+    fn arbitrary(src: &mut arbitrary::Unstructured<'_>) -> arbitrary::Result<Self> {
+        let sign = if bool::arbitrary(src)? {
+            Sign::Plus
+        } else {
+            Sign::Minus
+        };
+        let data = BigUint::arbitrary(src)?;
+        Ok(Self::from_biguint(sign, data))
+    }
+
+    fn size_hint(depth: usize) -> (usize, Option<usize>) {
+        arbitrary::size_hint::and(BigUint::size_hint(depth), bool::size_hint(depth))
+    }
+}
+
 #[test]
 fn test_from_biguint() {
     fn check(inp_s: Sign, inp_n: usize, ans_s: Sign, ans_n: usize) {

src/biguint.rs

@@ -3382,3 +3382,16 @@ fn test_set_digit() {
     assert_eq!(a.data.len(), 1);
     assert_eq!(a.data[0], 4);
 }
+
+// arbitrary support
+#[cfg(feature = "fuzz")]
+impl arbitrary::Arbitrary<'_> for BigUint {
+    fn arbitrary(src: &mut arbitrary::Unstructured<'_>) -> arbitrary::Result<Self> {
+        let data = SmallVec::arbitrary(src)?;
+        Ok(Self { data })
+    }
+
+    fn size_hint(depth: usize) -> (usize, Option<usize>) {
+        SmallVec::<[BigDigit; VEC_SIZE]>::size_hint(depth)
+    }
+}

src/monty.rs

@@ -1,8 +1,8 @@
 #![allow(clippy::many_single_char_names)]
 
-use num_traits::{One, Zero};
-use core::ops::Shl;
 use alloc::vec::Vec;
+use core::ops::Shl;
+use num_traits::{One, Zero};
 
 use crate::big_digit::{self, BigDigit, DoubleBigDigit, SignedDoubleBigDigit};
 use crate::biguint::BigUint;

tests/biguint.rs

@@ -20,8 +20,7 @@ use std::{i128, u128};
 use std::{u16, u32, u64, u8, usize};
 
 use num_traits::{
-    CheckedAdd, CheckedDiv, CheckedMul, CheckedSub, FromPrimitive, Num, One, Pow,
-    ToPrimitive, Zero,
+    CheckedAdd, CheckedDiv, CheckedMul, CheckedSub, FromPrimitive, Num, One, Pow, ToPrimitive, Zero,
 };
 
 use num_traits::float::FloatCore;