MSB LSB转换处理

Hackerpro

处理点阵显示的时候涉及到了MSB<-->LSB的转换，于是在找了些大神的资料
http://blog.csdn.net/kimylrong/article/details/30047867
文中的方法是针对32位数据的，字符数据往往是8位的；
我稍微改动了下
方法一：

1. u8 reverse(u8 x)
   
2. {
   
3.     x = (((x & 0xaa) >> 1) | ((x & 0x55) << 1));  
   
4.     x = (((x & 0xcc) >> 2) | ((x & 0x33) << 2));  
   
5.     return((x >> 4) | (x << 4));  
   
6. }

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优点：空间占用少；
缺点：很明显，有一定的运算量，字符那么多数据，每一个都这么处理还是有点差距的。
方法二：
查表法

1. const code BitReverseTable256[] =
   
2. {
   
3.         0X00,0x80,0x40,0xC0,0x20,0xA0,0x60,0xE0,0x10,0x90,0x50,0xD0,0x30,0xB0,0x70,0xF0,
   
4.         0x08,0x88,0x48,0xC8,0x28,0xA8,0x68,0xE8,0x18,0x98,0x58,0xD8,0x38,0xB8,0x78,0xF8,
   
5.         0x04,0x84,0x44,0xC4,0x24,0xA4,0x64,0xE4,0x14,0x94,0x54,0xD4,0x34,0xB4,0x74,0xF4,
   
6.         0x0C,0x8C,0x4C,0xCC,0x2C,0xAC,0x6C,0xEC,0x1C,0x9C,0x5C,0xDC,0x3C,0xBC,0x7C,0xFC,
   
7.         0x02,0x82,0x42,0xC2,0x22,0xA2,0x62,0xE2,0x12,0x92,0x52,0xD2,0x32,0xB2,0x72,0xF2,
   
8.         0x0A,0x8A,0x4A,0xCA,0x2A,0xAA,0x6A,0xEA,0x1A,0x9A,0x5A,0xDA,0x3A,0xBA,0x7A,0xFA,
   
9.         0x06,0x86,0x46,0xC6,0x26,0xA6,0x66,0xE6,0x16,0x96,0x56,0xD6,0x36,0xB6,0x76,0xF6,
   
10.         0x0E,0x8E,0x4E,0xCE,0x2E,0xAE,0x6E,0xEE,0x1E,0x9E,0x5E,0xDE,0x3E,0xBE,0x7E,0xFE,
    
11.         0x01,0x81,0x41,0xC1,0x21,0xA1,0x61,0xE1,0x11,0x91,0x51,0xD1,0x31,0xB1,0x71,0xF1,
    
12.         0x09,0x89,0x49,0xC9,0x29,0xA9,0x69,0xE9,0x19,0x99,0x59,0xD9,0x39,0xB9,0x79,0xF9,
    
13.         0x05,0x85,0x45,0xC5,0x25,0xA5,0x65,0xE5,0x15,0x95,0x55,0xD5,0x35,0xB5,0x75,0xF5,
    
14.         0x0D,0x8D,0x4D,0xCD,0x2D,0xAD,0x6D,0xED,0x1D,0x9D,0x5D,0xDD,0x3D,0xBD,0x7D,0xFD,
    
15.         0x03,0x83,0x43,0xC3,0x23,0xA3,0x63,0xE3,0x13,0x93,0x53,0xD3,0x33,0xB3,0x73,0xF3,
    
16.         0x0B,0x8B,0x4B,0xCB,0x2B,0xAB,0x6B,0xEB,0x1B,0x9B,0x5B,0xDB,0x3B,0xBB,0x7B,0xFB,
    
17.         0x07,0x87,0x47,0xC7,0x27,0xA7,0x67,0xE7,0x17,0x97,0x57,0xD7,0x37,0xB7,0x77,0xF7,
    
18.         0x0F,0x8F,0x4F,0xCF,0x2F,0xAF,0x6F,0xEF,0x1F,0x9F,0x5F,0xDF,0x3F,0xBF,0x7F,0xFF
    
19. };
    
20. u8 reverse(u8 x)
    
21. {
    
22.         return BitReverseTable256[x];
    
23. }

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优点：贼快，也可以不用函数，直接调用数组；
缺点：略占点空间，但是一般不缺这点空间吧。

pathletboy

256可以砍半，加入适当运算，只需要128字节的表。

Hackerpro

pathletboy 发表于 2017-7-3 12:52
256可以砍半，加入适当运算，只需要128字节的表。

是的，这就要权衡时间还是空间了