FFT Computation using CMSIS DSP library

I have a code that computes FFT using fftpack functions npy_rffti and npy_rfftf . I want to replace them using arm library functions. I have a real signal. I wrote the below code.

arm_rfft_fast_instance_f32 rfft_instance;

arm_rfft_fast_init_f32(&rfft_instance, 1024);

static float32_t *rfft_result;

rfft_result = malloc(n * sizeof(float32_t));

arm_rfft_fast_f32(&rfft_instance, accel_copy, rfft_result, 0);

Below is my existing code with fftpack functions:

int len_rffti = 2*n + 15; /* 15 extra 32-bit ints used as storage in fftpack's state */

Treal* rffti = malloc(len_rffti * sizeof(Treal));

npy_rffti(n, rffti); /* calculates rffti */

int len_buf = (n/2 + 1) * 2; /* n+1 if n is odd. otherwise n+2. buf[0] is DC component and is ignored */

Treal* buf = malloc(len_buf * sizeof(Treal));



/* fill raw accel signal into buffer */

buf[0] = 0.0f;

for (i = 0; i < n; i++) {

buf[i+1] = (Treal) accel[i];

}

/* calculate FFT.  puts FFT into buffer */

npy_rfftf(n, buf+1, rffti);

Both produce very different values of FFT. What am i doing wrong? Any help is appreciated. Thanks