Zero fill right shift in swift - ios

Question

(byte) ((val & 0xff00) >>> 8);
This is the Java code. I want to convert this code to Swift. But there is no >>> operator in swift. How can I use Zero fill right shift in Swift?

Answer 1

If you use the truncatingBitPattern initializer of integer types
to extract a byte then you don't have to mask the value and it does not matter if the shift operator fills with zeros or ones (which depends on whether the source
type is unsigned or signed).
Choose Int8 or UInt8 depending
on whether the byte should be interpreted as a signed or
unsigned number.
let value = 0xABCD
let signedByte = Int8(truncatingBitPattern: value >> 8)
print(signedByte) // -85
let unsignedByte = UInt8(truncatingBitPattern: value >> 8)
print(unsignedByte) // 171

Answer 2

Operator >> in Swift is zero-fill (for unsigned integers):
The bit-shifting behavior for unsigned integers is as follows:
Existing bits are moved to the left or right by the requested number of places.
Any bits that are moved beyond the bounds of the integer’s storage are discarded.
Zeros are inserted in the spaces left behind after the original bits are moved to the left or right.
https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/AdvancedOperators.html#//apple_ref/doc/uid/TP40014097-CH27-ID29

Answer 3

You don't need zero fill shift int this case because a byte is only 8-bits.
The code you have is the same as
(byte) (((val & 0xFF00) >> 8) & 0xFF)
or
(byte) ((val & 0xFF00) >> 8)
or
(byte) (val >> 8)

Answer 4

Zero-fill right shift operator doesn't exist in swift/objc, unfortunately. As an alternative / workaround:
// java
// let's say we want to zero-fill right shift 4 bits
int num = -333;
num >>>= 4; // num: 268435435
// objc
NSInteger num = -333;
num >>= 1;
if (num < 0) num ^= NSIntegerMin;
num >>= 3; // num: 268435435
// swift (assume we are dealing with 32 bit integer)
var num: Int32 = -333
num >>= 1
if num < 0 {
num ^= Int32.min
}
num >>= 3 // num: 268435435
Essentially get rid of the sign bit when negative.