BigInteger maximum length
.NET 9 enforces a maximum length of BigInteger, which is that it can contain no more than (2^31) - 1 (approximately 2.14 billion) bits. Such a number represents an almost 256 MB allocation and contains approximately 646.5 million digits. This new limit ensures that all APIs exposed are well behaved and consistent while still allowing numbers that are far beyond most usage scenarios.
Previous behavior
Previously, you could assign a value with a length up to Array.MaxLength * 32 bits to a BigInteger variable.
Note
Typical machines would hit an OutOfMemoryException far before this limit could ever be reached.
New behavior
Starting in .NET 9, BigInteger has a maximum length of (2^31) - 1 (approximately 2.14 billion) bits. If you attempt to assign a larger value, an OverflowException is thrown at run time. For example, the following code throws an exception:
BigInteger bigInt = new BigInteger(-1) << int.MaxValue;
Version introduced
.NET 9 Preview 6
Type of breaking change
This change is a behavioral change.
Reason for change
BigInteger supports representing integer values of essentially arbitrary length. However, in practice, the length is constrained by limits of the underlying computer, such as available memory or how long it would take to compute a given expression. Additionally, there exist some APIs that fail given inputs that result in a value that's too large. For these reasons, a maximum length is now enforced.
Recommended action
If your code is affected, decrease the length of value you're assigning to BigInteger or add a length check.
