What's the largest value an NSNumber can store?

Question

What's the largest value an NSNumber can store?

// ok
    NSNumber *value = @(1 << 31); 

// gives compiler error, so max NSNumber is 32-bit uint?
    NSNumber *value = @(1 << 32); 

Shapely

The answers already answer the actual question, so I'll explain the error. The 1 in 1 << 32 is an int, and the compiler uses that when it performs the shift. Since an int is 32 bits, you cannot shift it 32 positions. If you used @(1ULL << 32), it would work, because 1ULL has a type of unsigned long long. – Presbyter

Why would this question be voted down? Down vote trolling? – Shapely

Answer 1

NSNumber is actually a class cluster, meaning that when you create an instance you may be getting any of a variety of concrete subclasses, each capable of storing a different kind of numeric type. The actual types available, and their sizes, may be machine-dependent.

Looking at the NSNumber documentation shows you the different kinds of numbers you can store: the two largest integer options would be +numberWithLongLong: (or +numberWithUnsignedLongLong:), which stores a long long, and +numberWithInteger: (or +numberWithUnsignedInteger:), which stores an NSInteger. The maximum NSNumber values are therefore limited by these types.

The Foundation documentation states:

When building 32-bit applications, NSInteger is a 32-bit integer. A 64-bit application treats NSInteger as a 64-bit integer.

The compiler is smart and will create an NSNumber of the same type as your numeric literal. As mentioned in the comments above, you can use @(1ULL << 32) if your machine has an unsigned long long type with more than 32 bits.

Furthermore, NSNumber is toll-free bridged to CFNumber, meaning you can try out functions like CFNumberGetByteSize() for yourself — and have a look at the CFNumberType documentation. You'll see these are basically the same as the NSNumber options.

Additionally, the NSDecimalNumber class, a subclass of NSNumber, provides the +maximumDecimalNumber method which you can use to find the maximum value that can be stored in an NSDecimalNumber. NSDecimalNumber, and the floating-point types, may be able to store bigger numbers than the integer types, though with decreasing precision.

Lacour

What about NSNumber *value = @(pow(2, 128));? – Stanwin

@Stanwin Since pow returns a double, the compiler will use +numberWithDouble: (or something equivalent to this). – Lacour

The largest integer that you could store then, would be using an unsigned long long, which is 64 bit. (18,446,744,073,709,551,615). NSDecimalNumber is technically a different class, and therefore has a different max number. – Nelly

Thanks, all. I updated my answer to address the maximum values of different types. – Lacour

@Nelly Your comment should be the accepted answer. – Frazzled