util: Add ConsumeArithUInt256InRange fuzzing helper

Author: marcofleon

src/test/fuzz/util.h

@@ -180,6 +180,22 @@ template <typename WeakEnumType, size_t size>
     return UintToArith256(ConsumeUInt256(fuzzed_data_provider));
 }
 
+[[nodiscard]] inline arith_uint256 ConsumeArithUInt256InRange(FuzzedDataProvider& fuzzed_data_provider, const arith_uint256& min, const arith_uint256& max) noexcept
+{
+    assert(min <= max);
+    const arith_uint256 range = max - min;
+    const arith_uint256 value = ConsumeArithUInt256(fuzzed_data_provider);
+    arith_uint256 result = value;
+    // Avoid division by 0, in case range + 1 results in overflow.
+    if (range != ~arith_uint256(0)) {
+        const arith_uint256 quotient = value / (range + 1);
+        result = value - (quotient * (range + 1));
+    }
+    result += min;
+    assert(result >= min && result <= max);
+    return result;
+}
+
 [[nodiscard]] std::map<COutPoint, Coin> ConsumeCoins(FuzzedDataProvider& fuzzed_data_provider) noexcept;
 
 [[nodiscard]] CTxDestination ConsumeTxDestination(FuzzedDataProvider& fuzzed_data_provider) noexcept;