static void lsp2poly(float *lsp, float *f) {
    int i, j;

    f[-1] = 0.0;
    f[ 0] = 1.0;
#if 0
    for(i=0; i<5; i++) {
        int idx_lsp = 2*i;
        f[i+1] = -lsp[idx_lsp]*f[i] + 2.0*f[i-1];
        for(j=i; j>0; j--) {
            f[j] += -lsp[idx_lsp]*f[j-1] + f[j-2];
        }
    }
#else
    f[1] = -2*lsp[0];
    for(i=1; i<5; i++) {
        float b = -2*lsp[2*i];
        f[i+1] = b*f[i] + 2.0*f[i-1];
        for(j=i; j>1; j--) {
            f[j] += b*f[j-1] + f[j-2];
        }
	f[1]+=b;
    }
#endif
}