Function mult

strings/dtoa.c:929–977

/* Multiply two Bigint numbers */

static Bigint *mult(Bigint *a, Bigint *b, Stack_alloc *alloc)
{
  Bigint *c;
  int k, wa, wb, wc;
  ULong *x, *xa, *xae, *xb, *xbe, *xc, *xc0;
  ULong y;
  ULLong carry, z;

  if (a->wds < b->wds)
  {
    c= a;
    a= b;
    b= c;
  }
  k= a->k;
  wa= a->wds;
  wb= b->wds;
  wc= wa + wb;
  if (wc > a->maxwds)
    k++;
  c= Balloc(k, alloc);
  for (x= c->p.x, xa= x + wc; x < xa; x++)
    *x= 0;
  xa= a->p.x;
  xae= xa + wa;
  xb= b->p.x;
  xbe= xb + wb;
  xc0= c->p.x;
  for (; xb < xbe; xc0++)
  {
    if ((y= *xb++))
    {
      x= xa;
      xc= xc0;
      carry= 0;
      do
      {
        z= *x++ * (ULLong)y + *xc + carry;
        carry= z >> 32;
        *xc++= (ULong) (z & FFFFFFFF);
      }
      while (x < xae);
      *xc= (ULong) carry;
    }
  }
  for (xc0= c->p.x, xc= xc0 + wc; wc > 0 && !*--xc; --wc) ;
  c->wds= wc;
  return c;
}


/*