I have some binary data that encodes a two byte value as a signed integer.
bytes[1] = 255 // 0xFF
bytes[2] = 251 // 0xF1
This is fairly easy - I can extract an Int16
value from these bytes with:
Int16(bytes[1]) << 8 | Int16(bytes[2])
This is where I'm running into issues. Most of my data spec called for UInt
and that is easy but I'm having trouble extracting the two bytes that make up an Int16
let nv : Int16 = -15
UInt8(nv >> 8) // fail
UInt8(nv) // fail
How would I extract the two bytes that make up an Int16
value
You should work with unsigned integers:
let bytes: [UInt8] = [255, 251]
let uInt16Value = UInt16(bytes[0]) << 8 | UInt16(bytes[1])
let uInt8Value0 = uInt16Value >> 8
let uInt8Value1 = UInt8(uInt16Value & 0x00ff)
If you want to convert UInt16 to bit equivalent Int16 then you can do it with specific initializer:
let int16Value: Int16 = -15
let uInt16Value = UInt16(bitPattern: int16Value)
And vice versa:
let uInt16Value: UInt16 = 65000
let int16Value = Int16(bitPattern: uInt16Value)
In your case:
let nv: Int16 = -15
let uNv = UInt16(bitPattern: nv)
UInt8(uNv >> 8)
UInt8(uNv & 0x00ff)
You could use init(truncatingBitPattern: Int16)
initializer:
let nv: Int16 = -15
UInt8(truncatingBitPattern: nv >> 8) // -> 255
UInt8(truncatingBitPattern: nv) // -> 241
I would just do this:
let a = UInt8(nv >> 8 & 0x00ff) // 255
let b = UInt8(nv & 0x00ff) // 241
extension Int16 {
var twoBytes : [UInt8] {
let unsignedSelf = UInt16(bitPattern: self)
return [UInt8(truncatingIfNeeded: unsignedSelf >> 8),
UInt8(truncatingIfNeeded: unsignedSelf)]
}
}
var test : Int16 = -15
test.twoBytes // [255, 241]
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