# init(sign:exponent:significand:) Creates a new value from the given sign, exponent, and significand. ``` init(sign: FloatingPointSign, exponent: Int, significand: Float) ``` ## Parameters `sign` The sign to use for the new value. `exponent` The new value’s exponent. `significand` The new value’s significand. ## Discussion The following example uses this initializer to create a new `Double` instance. `Double` is a binary floating-point type that has a radix of `2`. ``` let x = Double(sign: .plus, exponent: -2, significand: 1.5) // x == 0.375 ``` This initializer is equivalent to the following calculation, where `**` is exponentiation, computed as if by a single, correctly rounded, floating-point operation: ``` let sign: FloatingPointSign = .plus let exponent = -2 let significand = 1.5 let y = (sign == .minus ? -1 : 1) * significand * Double.radix ** exponent // y == 0.375 ``` As with any basic operation, if this value is outside the representable range of the type, overflow or underflow occurs, and zero, a subnormal value, or infinity may result. In addition, there are two other edge cases: - If the value you pass to `significand` is zero or infinite, the result is zero or infinite, regardless of the value of `exponent`. - If the value you pass to `significand` is NaN, the result is NaN. For any floating-point value `x` of type `F`, the result of the following is equal to `x`, with the distinction that the result is canonicalized if `x` is in a noncanonical encoding: ``` let x0 = F(sign: x.sign, exponent: x.exponent, significand: x.significand) ``` This initializer implements the `scaleB` operation defined by the [IEEE 754 specification](http://ieeexplore.ieee.org/servlet/opac?punumber=4610933). --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)