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Subject: Interesting answer to my rotation question from news:comp.algorithms

Author: Dann Corbit

Date: 20:45:01 06/06/02


uint64 flip(uint64 a)
{
  a =  (a&0xf0f0f0f00f0f0f0f)
      |(a&0x0f0f0f0f00000000)>>28
      |(a&0x00000000f0f0f0f0)<<28;
  a =  (a&0xcccc3333cccc3333)
      |(a&0x3333000033330000)>>14
      |(a&0x0000cccc0000cccc)<<14;
  return (a&0xaa55aa55aa55aa55)
        |(a&0x5500550055005500)>>7
        |(a&0x00aa00aa00aa00aa)<<7;
}

uint64 rotate90(uint64 a)
  a =  (a&0xf0f0f0f000000000)>>32
      |(a&0x0f0f0f0f00000000)<<4
      |(a&0x00000000f0f0f0f0)>>4
      |(a&0x000000000f0f0f0f)<<32;
  a =  (a&0xcccc0000cccc0000)>>16
      |(a&0x3333000033330000)<<2
      |(a&0x0000cccc0000cccc)>>2
      |(a&0x0000333300003333)<<16;
  a =  (a&0xaa00aa00aa00aa00)>>8
      |(a&0x5500550055005500)<<1
      |(a&0x00aa00aa00aa00aa)<<8
      |(a&0x0055005500550055)>>1;
  return a;
}

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Last modified: Thu, 15 Apr 21 08:11:13 -0700

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