[英]How to Calculate the Square Root of a Float in C#
如何在C#
计算Float
平方根,类似于XNA中的Core.Sqrt
?
Calculate it for double
and then cast back to float. 将其计算为
double
,然后将其转换为float。 May be a bit slow, but should work. 可能有点慢,但应该工作。
(float)Math.Sqrt(inputFloat)
Hate to say this, but 0x5f3759df seems to take 3x as long as Math.Sqrt. 讨厌这样说,但0x5f3759df似乎需要3倍于Math.Sqrt。 I just did some testing with timers.
我只是对计时器进行了一些测试。 Math.Sqrt in a for-loop accessing pre-calculated arrays resulted in approx 80ms.
for循环访问预先计算的数组中的Math.Sqrt导致大约80ms。 0x5f3759df under the same circumstances resulted in 180+ms
在相同情况下0x5f3759df导致180 + ms
The test was conducted several times using the Release mode optimizations. 使用Release模式优化进行了多次测试。
Source below: 来源如下:
/*
================
SquareRootFloat
================
*/
unsafe static void SquareRootFloat(ref float number, out float result)
{
long i;
float x, y;
const float f = 1.5F;
x = number * 0.5F;
y = number;
i = *(long*)&y;
i = 0x5f3759df - (i >> 1);
y = *(float*)&i;
y = y * (f - (x * y * y));
y = y * (f - (x * y * y));
result = number * y;
}
/*
================
SquareRootFloat
================
*/
unsafe static float SquareRootFloat(float number)
{
long i;
float x, y;
const float f = 1.5F;
x = number * 0.5F;
y = number;
i = *(long*)&y;
i = 0x5f3759df - (i >> 1);
y = *(float*)&i;
y = y * (f - (x * y * y));
y = y * (f - (x * y * y));
return number * y;
}
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
int Cycles = 10000000;
Random rnd = new Random();
float[] Values = new float[Cycles];
for (int i = 0; i < Cycles; i++)
Values[i] = (float)(rnd.NextDouble() * 10000.0);
TimeSpan SqrtTime;
float[] Results = new float[Cycles];
DateTime Start = DateTime.Now;
for (int i = 0; i < Cycles; i++)
{
SquareRootFloat(ref Values[i], out Results[i]);
//Results[i] = (float)Math.Sqrt((float)Values[i]);
//Results[i] = SquareRootFloat(Values[i]);
}
DateTime End = DateTime.Now;
SqrtTime = End - Start;
Console.WriteLine("Sqrt was " + SqrtTime.TotalMilliseconds.ToString() + " long");
Console.ReadKey();
}
}
var result = Math.Sqrt((double)value);
private double operand1;
private void squareRoot_Click(object sender, EventArgs e)
{
operand1 = Math.Sqrt(operand1);
this.textBox1.Text = operand1.ToString();
}
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