OI中的黑科技

雷神之锤3, 快速逆平方根算法

Sample Code

static float invSqrt(float number) 
{
    volatile long i;
    volatile float x, y;
    volatile const float f = 1.5F;

    x = number * 0.5F;
    y = number;
    i = * (( long * ) &y);
    i = 0x5f375a86 - ( i >> 1 );
    y = * (( float * ) &i);
    y = y * ( f - ( x * y * y ) );
    return y;
}