# 算法实现

## 分治法并行反转

• 首先是2位2位为一组，交换前一半和后一半
• 再4位4位为一组，交换前一半和后一半
• 再8位为一组，交换前一半和后一半

• 2个2个为一组，交换前一半和后一半, 变成：2 1 4 3 6 5 8 7
• 4个4个为一组，交换前一半和后一半， 变成：4 3 2 1 8 7 6 5
• 再8个为一组，交换前一半和后一半, 变成：8 7 6 5 4 3 2 1

static byte ReverseBits(byte c)
{
c = (byte)(((byte)((byte)(c & 0x55) << 1)) | ((byte)((byte)(c & 0xAA) >> 1)));
c = (byte)(((byte)((byte)(c & 0x33) << 2)) | ((byte)((byte)(c & 0xCC) >> 2)));
c = (byte)(((byte)((byte)(c & 0x0F) << 4)) | ((byte)((byte)(c & 0xF0) >> 4)));
return c;
}

## 小表查表法

//不多不少的静态数据
static byte[] sta_4 = new byte[16]
{
0x00, 0x08, 0x04, 0x0C, 0x02, 0x0A, 0x06, 0x0E,
0x01, 0x09, 0x05, 0x0D, 0x03, 0x0B, 0x07, 0x0F
};
static byte ReverseBits(byte c)
{
byte d = 0; //没有判断
d |= (byte)((sta_4[c&0xF]) << 4);
d |= sta_4[c>>4];
return d;
}

## 全表查表法

static byte[] sta_8 = new byte[256]
{
0x00,0x80,0x40,0xc0,0x20,0xa0,0x60,0xe0,0x10,0x90,0x50,0xd0,0x30,0xb0,0x70,0xf0,
0x08,0x88,0x48,0xc8,0x28,0xa8,0x68,0xe8,0x18,0x98,0x58,0xd8,0x38,0xb8,0x78,0xf8,
0x04,0x84,0x44,0xc4,0x24,0xa4,0x64,0xe4,0x14,0x94,0x54,0xd4,0x34,0xb4,0x74,0xf4,
0x0c,0x8c,0x4c,0xcc,0x2c,0xac,0x6c,0xec,0x1c,0x9c,0x5c,0xdc,0x3c,0xbc,0x7c,0xfc,
0x02,0x82,0x42,0xc2,0x22,0xa2,0x62,0xe2,0x12,0x92,0x52,0xd2,0x32,0xb2,0x72,0xf2,
0x0a,0x8a,0x4a,0xca,0x2a,0xaa,0x6a,0xea,0x1a,0x9a,0x5a,0xda,0x3a,0xba,0x7a,0xfa,
0x06,0x86,0x46,0xc6,0x26,0xa6,0x66,0xe6,0x16,0x96,0x56,0xd6,0x36,0xb6,0x76,0xf6,
0x0e,0x8e,0x4e,0xce,0x2e,0xae,0x6e,0xee,0x1e,0x9e,0x5e,0xde,0x3e,0xbe,0x7e,0xfe,
0x01,0x81,0x41,0xc1,0x21,0xa1,0x61,0xe1,0x11,0x91,0x51,0xd1,0x31,0xb1,0x71,0xf1,
0x09,0x89,0x49,0xc9,0x29,0xa9,0x69,0xe9,0x19,0x99,0x59,0xd9,0x39,0xb9,0x79,0xf9,
0x05,0x85,0x45,0xc5,0x25,0xa5,0x65,0xe5,0x15,0x95,0x55,0xd5,0x35,0xb5,0x75,0xf5,
0x03,0x83,0x43,0xc3,0x23,0xa3,0x63,0xe3,0x13,0x93,0x53,0xd3,0x33,0xb3,0x73,0xf3,
0x0b,0x8b,0x4b,0xcb,0x2b,0xab,0x6b,0xeb,0x1b,0x9b,0x5b,0xdb,0x3b,0xbb,0x7b,0xfb,
0x07,0x87,0x47,0xc7,0x27,0xa7,0x67,0xe7,0x17,0x97,0x57,0xd7,0x37,0xb7,0x77,0xf7,
0x0f,0x8f,0x4f,0xcf,0x2f,0xaf,0x6f,0xef,0x1f,0x9f,0x5f,0xdf,0x3f,0xbf,0x7f,0xff
};
static byte ReverseBits(byte c)
{
return sta_8[c];
}

## 64位内数据位序反转

//valueLength是待处理值的位数，如uint是32位数据
static UInt64 ReverseBits(UInt64 value, Int32 valueLength)
{
UInt64 output = 0;
for (var i = valueLength - 1; i >= 0; i--)
{
output |= (value & 1) << i;
value >>= 1;
}
return output;
}

## 任意位数据位序反转

• 以字节为单位将数据进行字节序反转
• 依次对单个字节进行位序反转

# 参考文章

posted @ 2020-07-31 15:03  time-flies  阅读(201)  评论(0编辑  收藏
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