- /********************************************************************
- 将单字节数据反序处理: 0B01001101 -> 0B10110010
- perl
- foreach $i (0..255)
- {
- $r = 0;
- foreach $j (0 .. 7 )
- {
- if (($i & ( 1<< $j)) != 0)
- {
- $r |= (1 << (7 - $j));
- }
- }
- print $r, ", ";
- if (($i & 7) == 7)
- {
- print "\n";
- }
- }
- http://graphics.stanford.edu/~seander/bithacks.html
- static const unsigned char reversed_byte[256] =
- {
- # define R2(n) n, n + 2*64, n + 1*64, n + 3*64
- # define R4(n) R2(n), R2(n + 2*16), R2(n + 1*16), R2(n + 3*16)
- # define R6(n) R4(n), R4(n + 2*4 ), R4(n + 1*4 ), R4(n + 3*4 )
- R6(0), R6(2), R6(1), R6(3)
- };
- *******************************************************************/
- static const unsigned char reversed_byte[256] =
- {
- 0, 128, 64, 192, 32, 160, 96, 224,
- 16, 144, 80, 208, 48, 176, 112, 240,
- 8, 136, 72, 200, 40, 168, 104, 232,
- 24, 152, 88, 216, 56, 184, 120, 248,
- 4, 132, 68, 196, 36, 164, 100, 228,
- 20, 148, 84, 212, 52, 180, 116, 244,
- 12, 140, 76, 204, 44, 172, 108, 236,
- 28, 156, 92, 220, 60, 188, 124, 252,
- 2, 130, 66, 194, 34, 162, 98, 226,
- 18, 146, 82, 210, 50, 178, 114, 242,
- 10, 138, 74, 202, 42, 170, 106, 234,
- 26, 154, 90, 218, 58, 186, 122, 250,
- 6, 134, 70, 198, 38, 166, 102, 230,
- 22, 150, 86, 214, 54, 182, 118, 246,
- 14, 142, 78, 206, 46, 174, 110, 238,
- 30, 158, 94, 222, 62, 190, 126, 254,
- 1, 129, 65, 193, 33, 161, 97, 225,
- 17, 145, 81, 209, 49, 177, 113, 241,
- 9, 137, 73, 201, 41, 169, 105, 233,
- 25, 153, 89, 217, 57, 185, 121, 249,
- 5, 133, 69, 197, 37, 165, 101, 229,
- 21, 149, 85, 213, 53, 181, 117, 245,
- 13, 141, 77, 205, 45, 173, 109, 237,
- 29, 157, 93, 221, 61, 189, 125, 253,
- 3, 131, 67, 195, 35, 163, 99, 227,
- 19, 147, 83, 211, 51, 179, 115, 243,
- 11, 139, 75, 203, 43, 171, 107, 235,
- 27, 155, 91, 219, 59, 187, 123, 251,
- 7, 135, 71, 199, 39, 167, 103, 231,
- 23, 151, 87, 215, 55, 183, 119, 247,
- 15, 143, 79, 207, 47, 175, 111, 239,
- 31, 159, 95, 223, 63, 191, 127, 255
- };
- //计算某HASH值的反向值
- static unsigned int reverse(unsigned int key)
- {
- return ((reversed_byte[key & 0xff] << 24) |
- (reversed_byte[(key >> 8) & 0xff] << 16) |
- (reversed_byte[(key >> 16) & 0xff] << 8) |
- (reversed_byte[(key >> 24) & 0xff]));
- }
复制代码 上面是一个hash表实现里代码,
位操作技巧:
http://graphics.stanford.edu/~seander/bithacks.html |