从短裤中得到 8 条短裤

Question

我有一个像这样的 a 短数组：

a = [ 16748, 
      26979, 
      25888, 
      30561, 
      115
    ] //in decimal

a = [ 0100000101101100, 
      0110100101100011, 
      0110010100100000, 
      0111011101100001, 
      0000000001110011
    ] //in binary

我想获得另一个 b 短裤数组，由表示每个短裤的每对位组成。（解释起来比较困难，举个例子就很容易理解）。

因此，对于数组 a 我将获得数组 b:

b = [ 01, 00, 00, 01, 01, 10, 11, 00, 
      01, 10, 10, 01, 01, 10, 00, 11, 
      01, 10, 01, 01, 00, 10, 00, 00, 
      01, 11, 01, 11, 01, 10, 00, 01, 
      00, 00, 00, 00, 01, 11, 00, 11
    ]

在伪代码中我想到了这样做：

int lenght = (16/2) * a.length; //16*2 because I had short (16 bit) and I want sequences of 2 bit
short[] b = new short[length]; //I create the new array of short
int j = 0; //counter of b array
foreach n in a { //foreach short in array a
    for(int i = 16 - 2; i > 0; i-2) { //shift of 2 positions to right
        b[j] = ( (n >> i) & ((2^2)-1) ); //shift and &
        j++;
    }
}

我试图将这个伪代码（假设它是正确的）翻译成 Java:

public static short[] createSequencesOf2Bit(short[] a) {
    int length = (16/2) * a.length; 
    short[] b = new short[length];

    for(int i = 0; i < a.length; i++) {
        int j = 0; 
        for(short c = 16 - 2; c > 0; c -= 2) {
            short shift = (short)(a[i] >> c);
            b[j] = (short)(shift & 0x11);
            j++;
        }
    }
    return b;
}

但是如果我打印 b[] 我得不到我想要的。例如，仅考虑 a (16748 = 0100000101101100) 中的第一个短路。我获得：

[1, 0, 16, 1, 1, 16, 17]

这是完全错误的。事实上我应该得到：

b = [ 01, 00, 00, 01, 01, 10, 11, 00,
      ...
    ] //in binary

b = [ 1, 0, 0, 1, 1, 2, 3, 0,
      ...
    ] //in decimal

有人可以帮助我吗？非常感谢。

这很奇怪。如果我只考虑 a 中的第一个短路并打印 b 我得到：

public static short[] createSequencesOf2Bit(short[] a) {
    int length = (16/2) * a.length; 
    short[] b = new short[length];

    //for(int i = 0; i < a.length; i++) {
        int j = 0; 
        for(short c = (16 - 2); c >= 0; c -= 2) {
            short shift = (short)(a[0] >> c);
            b[j] = (short)(shift & 0x3);
            j++;
        }
    //}
    for(int i = 0; i < b.length; i++) {
        System.out.println("b[" + i + "]: " + b[i]);
    }
    return b;
} 

b = [1 0 0 1 1 2 3 0 0 0 0 0 ... 0]

但是如果我打印这个：

public static short[] createSequencesOf2Bit(short[] a) {
    int length = (16/2) * a.length; 
    short[] b = new short[length];

    for(int i = 0; i < a.length; i++) {
        int j = 0; 
        for(short c = (16 - 2); c >= 0; c -= 2) {
            short shift = (short)(a[i] >> c);
            b[j] = (short)(shift & 0x3);
            j++;
        }
    }
    for(int i = 0; i < b.length; i++) {
        System.out.println("b[" + i + "]: " + b[i]);
    }
    return b;
} 

b = [0 0 0 0 1 3 0 3 0 0 0 0 ... 0]

Answer 1

我怀疑主要问题是您想要 & 0x3 而不是 & 0x11。记住 0x 表示十六进制，所以 0x11 给你数字 17，而不是 3。或者你可以写 0b11 得到二进制的 11。

此外，正如评论中指出的那样，循环条件应该是c >= 0，而不是c > 0。

从短裤中得到 8 条短裤

Get 8 shorts from a short

java

bit-manipulation

bitwise-operators

short