Re: lun - Lucky Number

Richard Heathfield in sci.crypt:

[...]

Tell you what, I'll let my source code do the talking and give
you a demo run at the end:

Thank you. Interesting.

tuwetest.c: gcc -o tuwetest tuwetest.c tuwe.c
>
#include "tuwe.h"
>
#include <stdio.h>
>
static void dump(const void *vb, int n)
{
  int i = 0;
  int j = 0;
  const unsigned char * b = vb;
  for(i = 0; i < n; i++)
  {
    for(j = 7; j >= 0; j--)
    {
      fprintf(stdout, "%d", !!(b[i] & (1 << j)));

                              ^^
What does this do? Is it necessary?
(As you see, I'm not a C programmer. ;-)

    }
    putchar('\n');
  }
  printf("--------\n");
}
>
int main(void)
{
  unsigned char t[8] = {31, 41, 59, 26, 53, 58, 97, 32};
  unsigned char r[8] = {0, 0, 0, 0, 0, 0, 0, 0};
  unsigned char l[8] = {0, 0, 0, 0, 0, 0, 0, 0};
>
  puts("t first");
  dump(t, 8);
  puts("now turn it right 90 deg");
  tuwer(r, t);
  dump(r, 8);
  puts("and back again");
  tuwel(l, r);
  dump(t, 8);

"dump(l, 8);" (?)

  return 0;
}

[...]

#define BIT_QRY(x,i) ((x[(i)>>3] & (1<<((i)&7)))!=0)
#define BIT_SET(x,i) (x)[(i)>>3]|=(1<<((i)&7))
#define BIT_CLR(x,i) (x)[(i)>>3]&=(1<<((i)&7))^0xFF

Can you explain this a little bit?

Marcel
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