如何仅替换1字节的4位？

Question

我知道我可以在1字节内存储和检索2个4位数字，如下所示：

// Store both numbers in one byte
byte firstNumber = 10;
byte secondNumber = 15;
byte bothNumbers = (byte) ((firstNumber << 4) | secondNumber);

// Retreive the original numbers
firstNumber = (byte) ((bothNumbers >> 4) & (byte) 0x0F);
secondNumber = (byte) (bothNumbers & 0x0F);

但是，我如何在不触及最后4位（15）的情况下覆盖这两个数字中的一个（比如第一个（10））？

// Store both numbers in one byte
byte firstNumber = 10;
byte secondNumber = 15;
byte bothNumbers = (byte) ((firstNumber << 4) | secondNumber);

// Replacing one of the 2 numbers without touching the other
firstNumber = 13;
bothNumbers = ...

Answer 1

在静态编程语言中，您可以创建一个值类以方便使用。它只编译为Byte，但您可以方便地将其视为类实例/可装箱原语。

@JvmInline
value class FourBitPair(val bothNumbers: Byte) {
    constructor(firstNumber: Byte, secondNumber: Byte):
            this((firstNumber.toInt() shl 4 or secondNumber.toInt()).toByte())

    val firstNumber: Byte get() = ((bothNumbers.toInt() shr 4) and 0xF).toByte()
    val secondNumber: Byte get() = (bothNumbers.toInt() and 0xF).toByte()

    operator fun component1() = firstNumber
    operator fun component2() = secondNumber

    fun withFirstNumber(newFirstNumber: Byte) = FourBitPair(newFirstNumber, secondNumber)
    fun withSecondNumber(newSecondNumber: Byte) = FourBitPair(firstNumber, newSecondNumber)

    override fun toString(): String = "[$firstNumber, $secondNumber]"
}

fun main() {
    val x: Byte = 3
    val y: Byte = 15
    var pair = FourBitPair(x, y)
    println(pair)
    pair = pair.withFirstNumber(13)
    println(pair)
    pair = pair.withSecondNumber(4)
    println(pair)
    val (first, second) = pair
    println(second)
    println(pair.bothNumbers)
}

打印：

[3, 15]
[13, 15]
[13, 4]
4
-44

Answer 2

你会使用这样的东西：

bothNumbers = (byte) ((bothNumbers & 0xf) | (firstNumber << 4))