Java将长整数转换为字节-哪种方法更有效 [英] Java Converting long to bytes - which approach is more efficient

问题描述

我有两种方法可以将long转换为字节数组.

I have two approaches to convert long to byte array.

for (int i = 0; i < 7; i++) {
    data[pos + i] = (byte) (value >> (7- i - 1 << 3));
}

和

for (int i = 7; i >= 0; --i) {
    data[p + i] = (byte)(newl & 0xff);
    newl >>= 8;
}

这两个操作中哪个更有效?

which of the two operations is more efficient?

推荐答案

我建议您看看Java代码是如何做到的.

I suggest you look at how the Java code does it.

public final void writeLong(long v) throws IOException {
    writeBuffer[0] = (byte)(v >>> 56);
    writeBuffer[1] = (byte)(v >>> 48);
    writeBuffer[2] = (byte)(v >>> 40);
    writeBuffer[3] = (byte)(v >>> 32);
    writeBuffer[4] = (byte)(v >>> 24);
    writeBuffer[5] = (byte)(v >>> 16);
    writeBuffer[6] = (byte)(v >>>  8);
    writeBuffer[7] = (byte)(v >>>  0);
    out.write(writeBuffer, 0, 8);
    incCount(8);
}

如您所见，没有循环，您的操作就会减少.

as you can see, without a loop you have less operation.

最快的方法是完全不执行此操作，而是使用Unsafe.writeLong()，因为这会花费很长时间并将其直接放入内存中，而不是将其分解为字节.这样可以快十倍以上.

The fastest way is to not do this at all and instead using Unsafe.writeLong() as this take a long and places it directly into memory instead of breaking it into bytes. This can be more than 10x faster.

这篇关于Java将长整数转换为字节-哪种方法更有效的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！