Square root source code found on the net

I'm looking for some algorithm for square root calculation and found this source file. I would like to try to replicate it because it seems quite simple but I can not relate it to some known algorithm (Newton, Babylon ...). Can you tell me the name?

int sqrt(int num) {
    int op = num;
    int res = 0;
    int one = 1 << 30; // The second-to-top bit is set: 1L<<30 for long

    // "one" starts at the highest power of four <= the argument.
    while (one > op)
        one >>= 2;

    while (one != 0) {
        if (op >= res + one) {
            op -= res + one;
            res += 2 * one;
        }
        res >>= 1;
        one >>= 2;
    }
    return res;
}

As @Eugene Sh. references, this is the classic "digit-by-digit" method done to calculate square root. Learned it in base 10 when such things were taught in primary school.

OP's code fails select numbers too. sqrt(1073741824) --> -1 rather than expected 32768. 1073741824 == 0x40000000. Further, it fails most (all?) values this and greater. Of course OP's sqrt(some_negative) is a problem too.

Candidate alternative: also here

unsigned isqrt(unsigned num) {
  unsigned res = 0;
  
  // The second-to-top bit is set: 1 << 30 for 32 bits
  // Needs work to run on unusual platforms where `unsigned` has padding or odd bit width.
  unsigned bit = 1u << (sizeof(num) * CHAR_BIT - 2); 

  // "bit" starts at the highest power of four <= the argument.
  while (bit > num) {
    bit >>= 2;
  }

  while (bit > 0) {
    if (num >= res + bit) {
      num -= res + bit;
      res = (res >> 1) + bit;  // Key difference between this and OP's code
    } else {
      res >>= 1;
    }
    bit >>= 2;
  }

  return res;
}

Portability update. The greatest power of 4 is needed.

#include <limits.h>
// greatest power of 4 <= a power-of-2 minus 1
#define POW4_LE_POW2M1(n) (  ((n)/2 + 1) >> ((n)%3==0)  )

unsigned bit = POW4_LE_POW2M1(UINT_MAX);