将4位半字节设置为int类型

你非常亲密；

    public static int setNibble(int num, int nibble, int which)    {        int output;        if(which ==0)        { output = (num &  0xFFFFFFF0 ) | nibble;        }        else        { int shiftNibble = nibble << (4*which) ; int shiftMask = 0x0000000F << (4*which) ; output = (num & ~shiftMask) | shiftNibble ;        }        return output;    }

实际上，您可以简化代码，但要以区分大小写为代价

which == 0

if

not

    public static int setNibble(int num, int nibble, int which) {        int shiftNibble= nibble << (4*which) ;        int shiftMask= 0x0000000F << (4*which) ;        return ( num & ~shiftMask ) | shiftNibble ;    }

遮罩的想法是完全清除小节将占据结果的相同4个位置。否则，该位置将在半字节为零的那些位中包含垃圾。例如

    // Nibble77776666555544443333222211110000    num=   0b01001010111101010100110101101010 ;    nibble=0b0010 ;  // 2    which= 3 ;    shiftNibble=      0b00000000000000000010000000000000 ;    shiftMask=        0b00000000000000001111000000000000 ;    num=   0b01001010111101010100110101101010 ;    ~shiftMask=       0b11111111111111110000111111111111 ;      num & ~shiftMask= 0b01001010111101010000110101101010 ;    // ~~~~  Cleared!    ( num & ~shiftMask )       | nibble        0b01001010111101010010110101101010 ;    // ~~~~  Fully set; no garbage!