FFT library in android Sdk [closed]

Question

I am working with android project.I need FFT algorithm to process the android accelerometer data.Is there FFT library available in android sdk?

Answer 1

You can use this class, which is fast enough for real time audio analysis

public class FFT {    int n, m;    // Lookup tables. Only need to recompute when size of FFT changes.   double[] cos;   double[] sin;    public FFT(int n) {       this.n = n;       this.m = (int) (Math.log(n) / Math.log(2));        // Make sure n is a power of 2       if (n != (1 << m))           throw new RuntimeException("FFT length must be power of 2");        // precompute tables       cos = new double[n / 2];       sin = new double[n / 2];        for (int i = 0; i < n / 2; i++) {           cos[i] = Math.cos(-2 * Math.PI * i / n);           sin[i] = Math.sin(-2 * Math.PI * i / n);       }    }    public void fft(double[] x, double[] y) {       int i, j, k, n1, n2, a;       double c, s, t1, t2;        // Bit-reverse       j = 0;       n2 = n / 2;       for (i = 1; i < n - 1; i++) {           n1 = n2;           while (j >= n1) {               j = j - n1;               n1 = n1 / 2;           }           j = j + n1;            if (i < j) {               t1 = x[i];               x[i] = x[j];               x[j] = t1;               t1 = y[i];               y[i] = y[j];               y[j] = t1;           }       }        // FFT       n1 = 0;       n2 = 1;        for (i = 0; i < m; i++) {           n1 = n2;           n2 = n2 + n2;           a = 0;            for (j = 0; j < n1; j++) {               c = cos[a];               s = sin[a];               a += 1 << (m - i - 1);                for (k = j; k < n; k = k + n2) {                   t1 = c * x[k + n1] - s * y[k + n1];                   t2 = s * x[k + n1] + c * y[k + n1];                   x[k + n1] = x[k] - t1;                   y[k + n1] = y[k] - t2;                   x[k] = x[k] + t1;                   y[k] = y[k] + t2;               }           }       }   } } 

Warning: this code appears to be derived from here, and has a GPLv2 license.