问题描述
我有以下的code使用pre计算的内存表做正弦/余弦函数。在下面的示例表中有1024 * 128的项目涵盖了所有的正弦/余弦值从0到2PI。我知道我可以使用正弦/余弦对称性,只能容纳值的1/4,但他们计算的价值时,我将有更多的IFS。
I have the following code doing Sin/Cos function using a pre-calculated memory table. in the following example the table has 1024*128 items covering all the Sin/Cos values from 0 to 2pi. I know I can use Sin/Cos symmetry and hold only 1/4 of the values but them I will have more 'ifs' when computing the value.
private const double PI2 = Math.PI * 2.0;
private const int TABLE_SIZE = 1024 * 128;
private const double TABLE_SIZE_D = (double)TABLE_SIZE;
private const double FACTOR = TABLE_SIZE_D / PI2;
private static double[] _CosineDoubleTable;
private static double[] _SineDoubleTable;
设置转换表
private static void InitializeTrigonometricTables(){
_CosineDoubleTable = new double[TABLE_SIZE];
_SineDoubleTable = new double[TABLE_SIZE];
for (int i = 0; i < TABLE_SIZE; i++){
double Angle = ((double)i / TABLE_SIZE_D) * PI2;
_SineDoubleTable[i] = Math.Sin(Angle);
_CosineDoubleTable[i] = Math.Cos(Angle);
}
}
该值是弧度双。
Value %= PI2; // In case that the angle is larger than 2pi
if (Value < 0) Value += PI2; // in case that the angle is negative
int index = (int)(Value * FACTOR); //from radians to index and casted in to an int
double sineValue = _SineDoubleTable[index]; // get the value from the table
我在找一个更快的方式做到这一点。以上4行〜全过程(执行数十亿次)的25%。
I'm looking for a faster way to do this. The above 4 lines are ~25% of the whole process (executed billions of times).
推荐答案
您可以尝试使用不安全code,以消除数组边界检查。结果
但即使是不安全的,优化的版本似乎并没有走近 Math.Sin 一的任何地方>。
You could try to use unsafe code to eliminate array bounds checking.
But even a unsafe, optimized version does not seem to come anywhere near Math.Sin.
结果:
(1) 00:00:57.3382769 // original version
(2) 00:00:31.9445928 // optimized version
(3) 00:00:21.3566399 // Math.Sin
code:
static double SinOriginal(double Value)
{
Value %= PI2;
if (Value < 0) Value += PI2;
int index = (int)(Value * FACTOR);
return _SineDoubleTable[index];
}
static unsafe double SinOptimized(double* SineDoubleTable, double Value)
{
int index = (int)(Value * FACTOR) % TABLE_SIZE;
return (index < 0) ? SineDoubleTable[index + TABLE_SIZE]
: SineDoubleTable[index];
}
测试程序:
InitializeTrigonometricTables();
Random random = new Random();
SinOriginal(random.NextDouble());
var sw = System.Diagnostics.Stopwatch.StartNew();
for (long i = 0; i < 1000000000L; i++)
{
SinOriginal(random.NextDouble());
}
sw.Stop();
Console.WriteLine("(1) {0} // original version", sw.Elapsed);
fixed (double* SineDoubleTable = _SineDoubleTable)
{
SinOptimized(SineDoubleTable, random.NextDouble());
sw = System.Diagnostics.Stopwatch.StartNew();
for (long i = 0; i < 1000000000L; i++)
{
SinOptimized(SineDoubleTable, random.NextDouble());
}
sw.Stop();
Console.WriteLine("(2) {0} // optimized version", sw.Elapsed);
}
Math.Sin(random.NextDouble());
sw = System.Diagnostics.Stopwatch.StartNew();
for (long i = 0; i < 1000000000L; i++)
{
Math.Sin(random.NextDouble());
}
sw.Stop();
Console.WriteLine("(3) {0} // Math.Sin", sw.Elapsed);
这篇关于快速正弦/余弦使用pre计算的翻译阵列的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!