[英]How do I generate a fixed-waveform table in C?
生成包含C中正弦波幅度(由1到-1表示)的任意长度的有符号浮点数组的最有效方法是什么?
As Carl Smotricz pointed out in his answer , you can easily write a simple C program to build a hard-coded array for you. 正如Carl Smotricz在他的回答中指出的那样,你可以轻松编写一个简单的C程序来为你构建一个硬编码数组。
The following code would do the trick: 以下代码可以解决这个问题:
int main(int argc, char * argv[])
{
const int tableSize = 10;
const char * fileName = "sin_table.txt";
int x;
FILE * file;
file = fopen(fileName, "w");
if (file == NULL) { printf("unable to open file\n"); return -1; }
fprintf(file, "float sin_table[%d] =\n{\n ", tableSize);
for (x = 0; x < tableSize; x++)
{
fprintf(file, "\t%f,\n", sinf(x*2*pi/tableSize));
}
fprintf(file, "};\n");
fclose(file);
return 0;
}
And the output would look like this: 输出看起来像这样:
float sin_table[10] =
{
0.000000,
0.587785,
0.951057,
0.951056,
0.587785,
-0.000000,
-0.587785,
-0.951057,
-0.951056,
-0.587785,
};
If you want something very fast use a table (as already suggested). 如果你想要一些非常快速的东西使用表(如已经建议的那样)。
Another approach is to simulate a little sine-oscillator and use it to generate your data-array. 另一种方法是模拟一个小正弦振荡器并使用它来生成数据阵列。
Here is an example how to do this: 以下是如何执行此操作的示例:
int main (int argc, char **args)
{
int i;
float data[1024];
float angle = 2.0f * 3.14 / 1024;
// start of the sine-wave:
float sinval = 0;
float cosval = 1;
// rotation per iteration
float delta_sin = sinf(angle);
float delta_cos = cosf(angle);
for (i=0; i<1024; i++)
{
// store current value:
data[i] = sinval;
// update the oscillator:
float s = sinval * delta_cos - cosval * delta_sin;
float c = sinval * delta_sin + cosval * delta_cos;
sinval = s;
cosval = c;
}
}
The trick behind this is, that we start with a fixed point in 2D-space, stored in 9sinval, cosval). 这背后的诀窍是,我们从2D空间中的一个固定点开始,存储在9sinval,cosval)。 Furthermore I precompute the parameters for a single rotation in (delta_cos, delta_sin). 此外,我预先计算了(delta_cos,delta_sin)中单个旋转的参数。
All I do in the loop is to rotate the point 1024 times with the fixed rotation. 我在循环中所做的就是用固定的旋转将点旋转1024次。 This creates a sin/cos pair per iteration. 这会在每次迭代时创建一个sin / cos对。 (note: it's the same as a complex multiplication). (注意:它与复数乘法相同)。
This method becomes unstable sooner or later and is not as exact as calling sin/cos in the loop. 这种方法迟早会变得不稳定,并不像在循环中调用sin / cos那样精确。
So it's not a good idea to create huge tables with it, but if you can live with a slight error and smallish tables up to ten thousand elements it's quite usable. 所以用它创建大型表并不是一个好主意,但是如果你可以忍受一些轻微的错误,并且小表可以容纳一万个元素,那么它就非常实用。 To get around that issue you could change the type to double, do proper rounding or re-normalize the result every n iterations. 要解决该问题,您可以将类型更改为double,进行适当的舍入或每n次迭代重新规范化结果。
Edit: Just tested the code with double and 1e9 iterations. 编辑:刚用双重和1e9迭代测试代码。 Works for me. 适合我。 I have a slight drift in the phase, but the results are still more exact than using single precision sinf/cosf. 我在相位上略有漂移,但结果仍然比使用单精度sinf / cosf更精确。
如果你不想要运行时开销,请自己编写一个程序,将所有值打印出来作为C数组声明/初始化,然后#include
该文件到你的程序中。
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