Type Property

exponentBitCount

The number of bits used to represent the type’s exponent.

Declaration

static var exponentBitCount: Int { get }

Discussion

A binary floating-point type’s exponentBitCount imposes a limit on the range of the exponent for normal, finite values. The exponent bias of a type F can be calculated as the following, where ** is exponentiation:

let bias = 2 ** (F.exponentBitCount - 1) - 1

The least normal exponent for values of the type F is 1 - bias, and the largest finite exponent is bias. An all-zeros exponent is reserved for subnormals and zeros, and an all-ones exponent is reserved for infinity and NaN.

For example, the Float type has an exponentBitCount of 8, which gives an exponent bias of 127 by the calculation above.

let bias = 2 ** (Float.exponentBitCount - 1) - 1
// bias == 127
print(Float.greatestFiniteMagnitude.exponent)
// Prints "127"
print(Float.leastNormalMagnitude.exponent)
// Prints "-126"

Relationships

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