void secure_set_bits_port()

in src/random/sampling_portable.c [15:49]

• 25 lines of code
• 4 McCabe index (conditional complexity)

void secure_set_bits_port(OUT pad_r_t *   r,
                          IN const size_t first_pos,
                          IN const idx_t *wlist,
                          IN const size_t w_size)
{
  assert(w_size <= MAX_WLIST_SIZE);

  // Ideally we would like to cast r.val but it is not guaranteed to be aligned
  // as the entire pad_r_t structure. Thus, we assert that the position of val
  // is at the beginning of r.
  bike_static_assert(offsetof(pad_r_t, val) == 0, val_wrong_pos_in_pad_r_t);
  uint64_t *a64 = (uint64_t *)r;
  uint64_t  val, mask;

  // The size of wlist can be either D or T. So, we set it to max(D, T)
  size_t pos_qw[MAX_WLIST_SIZE];
  size_t pos_bit[MAX_WLIST_SIZE];

  // Identify the QW position of every value, and the bit position inside this QW.
  for(size_t i = 0; i < w_size; i++) {
    int32_t w  = wlist[i] - first_pos;
    pos_qw[i]  = w >> 6;
    pos_bit[i] = BIT(w & MASK(6));
  }

  // Fill each QW in constant time
  for(size_t i = 0; i < (sizeof(*r) / sizeof(uint64_t)); i++) {
    val = 0;
    for(size_t j = 0; j < w_size; j++) {
      mask = (-1ULL) + (!secure_cmp32(pos_qw[j], i));
      val |= (pos_bit[j] & mask);
    }
    a64[i] = val;
  }
}