Array shuffle

perm.c

#define xglue(x, y) x##y
#define glue(x, y) xglue(x, y)
#define uniqid(name) glue(name, __LINE__)

#ifdef _MSC_VER
#define swap(a,b) do { decltype((a) + 0) _t = (a); (a) = (b); (b) = _t; } while(0)
#else
#define swap(a,b) do {__typeof__((a) + 0) _t = (a); (a) = (b); (b) = _t; } while(0)
#endif

static void
seq_fix(int *p, int n) {
  for (int i = 0; i < n; ++i) {
    p[i] = -1 - p[i];
  }
}
#define arr_shfl(a,n,p) do {                            \
  for (int uniqid(i) = 0; uniqid(i) < n; ++uniqid(i)) { \
    if (p[uniqid(i)] >= 0) {                            \
      int uniqid(j) = uniqid(i);                        \
      while (p[uniqid(j)] != uniqid(i)) {               \
        const int uniqid(d) = p[uniqid(j)];             \
        swap(a[uniqid(j)], a[uniqid(d)]);               \
        p[uniqid(j)] = -1 - uniqid(d);                  \
        uniqid(j) = uniqid(d);                          \
      } p[uniqid(j)] = -1 - p[uniqid(j)];               \
    }                                                   \
}} while (0)

extern int
main(void) {
  int seq[] = {5,4,3,2,1,0};
  const char *data[] = {
    "0.0f",
    "1.0f",
    "2.0f",
    "3.0f",
    "4.0f",
    "5.0f",
  };
  arr_shfl(data, 6, seq);
  for (int i = 0; i < 6; ++i) {
    printf("%s\n", data[i]);
  }
  seq_fix(seq,6);
  for (int i = 0; i < 6; ++i) {
    printf("%d\n", seq[i]);
  }
  return 0;
}