Declaring types of argument variables outside the function headers in C

Question

I was going through the list of functions written by Jon Shewchuk for basic geometric predicates when I came across functions like doubleprint which purports to print the bit representation of a double. It is defined as

void doubleprint(number)
double number;
{
  unsigned long long no;
  unsigned long long sign, expo;
  .
  .
  printf("_%d  (%d)", exponent, exponent - 1 - bottomi);
  }
}

I would have imagined the function header would be void doubleprint(double number). Strangely the above function seems to compile with gcc 4.8.2.

Is this some special construct in C or is it equal to the "traditional" way of defining functions?