坐标计算目标C

我有以下功能,我是如此接近破解,但找不到一个在obj-c的mod函数。我希望有人能帮助suss这一点。

-(void)estimatePosition{
    float lat1 = 50.000;
    float lon1 = -1.666;
    float d = 500;
    float tc = 90;

    float lat;
    float dlon;
    float lon;

    lat =asin(sin(lat1)*cos(d)+cos(lat1)*sin(d)*cos(tc));
    dlon=atan2(sin(tc)*sin(d)*cos(lat1),cos(d)-sin(lat1)*sin(lat));
    lon=mod(lon1-dlon +M_PI,2*M_PI )-M_PI;
}