div without mul, div and mod

main.cpp

#include <cstdio>

int divImpl(int a, int b, int c, int * acc) {
	if (a < b) {
		return a;
	}
	int ret = divImpl(a, b + b, c + c, acc);
	if (ret >= b) {
		*acc += c;
		ret -= b;
	}
	return ret;
}

int div(int a, int b) {
	if (b == 0) {
		return -1;
	}
	int acc = 0;
	divImpl(a, b, 1, &acc);
	return acc;
}

int main() {
	printf("%d\n", div(20000000, 9));
	return 0;
}

fork 了一個 loop 版的。