Wt

This function

char *round_str(double d, int digits, char *buf) {
  static constint exp[] = { 1, 10, 100, 1000, 10000, 100000, 1000000 };

  long long i = static_cast<longlong>(d * exp[digits] + (d > 0 ? 0.49 : -0.49));
  lltoa(i, buf);
  char *num = buf;

  if (num[0] == '-')
    ++num;
  int len = std::strlen(num);

  if (len <= digits) {
    int shift = digits + 1 - len;
    for (int i = digits + 1; i >= 0; --i) {
      if (i >= shift)
       num[i] = num[i - shift];
      else
       num[i] = '0';
    }
    len = digits + 1;
  }
  int dotPos = (std::max)(len - digits, 0);
  for (int i = digits + 1; i >= 0; --i)
    num[dotPos + i + 1] = num[dotPos + i];
  num[dotPos] = '.';

  return buf;
}

does not work if there are more than 6 digits requested. The broken lines are

  static constint exp[] = { 1, 10, 100, 1000, 10000, 100000, 1000000 };

  long long i = static_cast<longlong>(d * exp[digits] + (d > 0 ? 0.49 : -0.49));

For some reason, there is a hard coded array of powers of ten. If a programmer passes, say, 7 as digits, this won't work. It wasn't segfaulting or anything, it was just giving out totally garbage data. Ideally this would just be something like

long long i = static_cast<longlong>(d * pow(10, digits) + (d > 0 ? 0.49 : -0.49));

If the array was being used for speed purposes, at least do something like

static constint exp[] = { 1, 10, 100, 1000, 10000, 100000, 1000000 };

long long i = static_cast<longlong>(d * (digits <= 6 ? exp[digits] : pow(10, digits)) + (d > 0 ? 0.49 : -0.49));