template<typename T> inline T read() {
  T X = 0; bool flag = 1; char ch = getchar();
  while (ch < '0' || ch > '9') {if (ch == '-') flag = 0; ch = getchar();}
  while (ch >= '0' && ch <= '9') {X = (X << 1) + (X << 3) + ch - '0'; ch = getchar();}
  if (flag) return X;
  return ~ (X - 1);
}

template<typename T> inline void write(T X) {
  if (X < 0) {putchar('-'); X = ~ (X - 1);}
  int s[50], top = 0;
  while (X) {s[++top] = X % 10; X /= 10;}
  if (!top) s[++top] = 0;
  while (top) putchar(s[top--] + '0');
  putchar('\n');
  return;
}

这个代码是什么意思？什么原理？