如何旋转居中的六边形位板?

这种排列有点混乱,每个相关位都有一个明显的移动距离。排列图如下所示(输出顶行):

不过,这确实说明了一些方法。如果我们靠近顶部看,每个“组”都是通过按升序从输入中收集一些位形成的,因此可以用7来完成 compress_right 操作aka PEXT

所以如果 佩克斯

uint64_t g0 = _pext_u64(in, 0x8080808);
uint64_t g1 = _pext_u64(in, 0x404040404);
uint64_t g2 = _pext_u64(in, 0x20202020202);
uint64_t g3 = _pext_u64(in, 0x1010101010101);
uint64_t g4 = _pext_u64(in, 0x808080808080);
uint64_t g5 = _pext_u64(in, 0x404040404000);
uint64_t g6 = _pext_u64(in, 0x202020200000);
uint64_t out = g0 |  (g1 << 7) |  (g2 << 14) | (g3 << 21) |
               (g4 << 28) | (g5 << 35) | (g6 << 42);

这种排列不能通过蝶形网络进行路由,但是Bene网络是通用的,因此可以工作。

所以可以用11个 these 置换步骤,也称为增量交换:

word bit_permute_step(word source, word mask, int shift) {
  word t;
  t = ((source >> shift) ^ source) & mask;
  return (source ^ t) ^ (t << shift);
  }

x = bit_permute_step(x, 0x1001400550054005, 1);
x = bit_permute_step(x, 0x2213223111023221, 2);
x = bit_permute_step(x, 0x01010B020104090E, 4);
x = bit_permute_step(x, 0x002900C400A7007B, 8);
x = bit_permute_step(x, 0x00000A0400002691, 16);
x = bit_permute_step(x, 0x0000000040203CAD, 32);
x = bit_permute_step(x, 0x0000530800001CE0, 16);
x = bit_permute_step(x, 0x000C001400250009, 8);
x = bit_permute_step(x, 0x0C00010403080104, 4);
x = bit_permute_step(x, 0x2012000011100100, 2);
x = bit_permute_step(x, 0x0141040000000010, 1);