Manipulating sc_biguint with raw pointer

[tmp_sc]

Hi, 

I want to set the value of `sc_biguint<128>` with `get_raw` method. 
If the value is just initialized to 0, I cannot do it.
E.g. 
 

  sc_biguint<128> val{0x00};
  
  cout << hex << val << endl;
  auto* ptr = val.get_raw();
  *ptr = 0x2AAABBBB;
  cout << hex << val << endl;

output is 
 

000000000000000000000000000000000
000000000000000000000000000000000

 

but in case it had some arithmetic operations, I can. 
E.g. 
 

  sc_biguint<128> val{0x00};

  val += 0xABCDEF0912345678; <--- difference
  
  cout << hex << val << endl;
  auto* ptr = val.get_raw();
  *ptr = 0x2AAABBBB;
  cout << hex << val << endl;

and the output is 

 

00000000000000000abcdef0912345678
00000000000000000abcdef092aaabbbb <--- value is changed

 

Any idea what is the reason for this feature?

[tmp_sc]

In the meantime I figured out:

Setting sc_biguint via get_raw pointer is not visible immediately because sc_uint (base class for sc_biguint) has several members. In this case most important ones are
 

private:

  small_type  sgn;         // Shortened as s.
...
  sc_digit *digit;                       // Shortened as d.

 

if we access through get_raw method

sc_digit* get_raw() const { return digit; }

we will update only digit, but not sgn . In case we want to print out the value of sc_biguint, at some moment we will call 
 

bool
sc_unsigned::iszero() const
{
  if (sgn == SC_ZERO)
    return true;

So without updating the sgn, we will get the value 0 even though digit is changed