とりあえず十進固定小数点の平方根でSQRT(20)前後を作ってみた

• れんしゅうで作った
• 精度は、ほぼない

プログラム

オンラインコンパイラ

#include <iostream>
using namespace std;

int q_rsqrt(int number) {
    
    long long i;
    long long x2, y;
    long long threehalfs;

    x2 = number * 1000000 / 2;
    y  = number * 1000000;
    threehalfs =  15 * 1000000 / 10;
    
    
    printf("x2 = %lld\n",x2);
    printf("y = %lld\n",y);
    printf("threehalfs = %lld\n",threehalfs);

    y = 304049 - (( 7812 * x2 )/1000000);
    printf("y = %lld\n",y);
    
    i = y * y / 1000000;
    i = x2 * i / 1000000;
    i = threehalfs - i;
    y = y * i / 1000000;
    printf("y = %lld\n",y);
    //y  = y * ( threehalfs - ( x2 * y * y ) );
    return y;
}


int main(void){
    // Your code here!
    
    int in = 20;
    int f;
    
    f = q_rsqrt(in);
    f = in * f;
    printf("%d.%d",f / 1000000,f % 1000000 );

}

x2 = 10000000
y = 20000000
threehalfs = 1500000
y = 225929
y = 223572
4.471440