FFT based Resampler admits NULL inputs/outputs

lib/include/srslte/phy/resampling/resampler.h

@@ -73,6 +73,12 @@ typedef struct {
  */
 SRSLTE_API int srslte_resampler_fft_init(srslte_resampler_fft_t* q, srslte_resampler_mode_t mode, uint32_t ratio);
 
+/**
+ * @brief resets internal re-sampler state
+ * @param q Object pointer
+ */
+SRSLTE_API void srslte_resampler_fft_reset_state(srslte_resampler_fft_t* q);
+
 /**
  * Get delay from the FFT based resampler.
  * @param q Object pointer
@@ -81,7 +87,11 @@ SRSLTE_API int srslte_resampler_fft_init(srslte_resampler_fft_t* q, srslte_resam
 SRSLTE_API uint32_t srslte_resampler_fft_get_delay(srslte_resampler_fft_t* q);
 
 /**
- * Run FFT based resampler in the initiated mode.
+ * @brief Run FFT based resampler in the initiated mode.
+ *
+ * @note Setting the input to NULL is equivalent of feeding zeroes
+ * @note Setting the output to NULL is equivalent of dropping output samples
+ *
  * @param q Object pointer, make sure it has been initialised
  * @param input Points at the input complex buffer
  * @param output Points at the output complex buffer

lib/src/phy/resampling/resampler.c

@@ -56,6 +56,10 @@ int srslte_resampler_fft_init(srslte_resampler_fft_t* q, srslte_resampler_mode_t
     return SRSLTE_ERROR_OUT_OF_BOUNDS;
   }
 
+  if (q->mode == mode && q->ratio == ratio) {
+    return SRSLTE_SUCCESS;
+  }
+
   // Make sure interpolator is freed
   srslte_resampler_fft_free(q);
 
@@ -142,26 +146,32 @@ int srslte_resampler_fft_init(srslte_resampler_fft_t* q, srslte_resampler_mode_t
   float norm = 1.0f / (cabsf(q->out_buffer[0]) * (float)input_fft_size);
   srslte_vec_sc_prod_cfc(q->out_buffer, norm, q->filter, high_size);
 
-  // Zero state
+  // reset state
-  q->state_len = 0;
+  srslte_resampler_fft_reset_state(q);
-  srslte_vec_cf_zero(q->state, output_fft_size);
 
   return SRSLTE_SUCCESS;
 }
 
+void srslte_resampler_fft_reset_state(srslte_resampler_fft_t* q)
+{
+  q->state_len = 0;
+  srslte_vec_cf_zero(q->state, q->ifft.size);
+}
+
 static void resampler_fft_interpolate(srslte_resampler_fft_t* q, const cf_t* input, cf_t* output, uint32_t nsamples)
 {
   uint32_t count = 0;
 
-  if (q == NULL || input == NULL || output == NULL) {
+  if (q == NULL) {
     return;
   }
 
   while (count < nsamples) {
     uint32_t n = SRSLTE_MIN(q->window_sz, nsamples - count);
 
+    if (input) {
       // Copy input samples
-    srslte_vec_cf_copy(q->in_buffer, &input[count], q->window_sz);
+      srslte_vec_cf_copy(q->in_buffer, &input[count], n);
 
       // Pad zeroes
       srslte_vec_cf_zero(&q->in_buffer[n], q->fft.size - n);
@@ -179,12 +189,18 @@ static void resampler_fft_interpolate(srslte_resampler_fft_t* q, const cf_t* inp
 
       // Execute iFFT
       srslte_dft_run_guru_c(&q->ifft);
+    } else {
+      // Equivalent IFFT output of feeding zeroes
+      srslte_vec_cf_zero(q->out_buffer, q->ifft.size);
+    }
 
     // Add previous state
     srslte_vec_sum_ccc(q->out_buffer, q->state, q->out_buffer, q->state_len);
 
     // Copy output
+    if (output) {
       srslte_vec_cf_copy(&output[count * q->ratio], q->out_buffer, n * q->ratio);
+    }
 
     // Save current state
     q->state_len = q->ifft.size - n * q->ratio;
@@ -206,6 +222,7 @@ static void resampler_fft_decimate(srslte_resampler_fft_t* q, const cf_t* input,
   while (count < nsamples) {
     uint32_t n = SRSLTE_MIN(q->window_sz, nsamples - count);
 
+    if (input) {
       // Copy input samples
       srslte_vec_cf_copy(q->in_buffer, &input[count], q->window_sz);
 
@@ -224,12 +241,17 @@ static void resampler_fft_decimate(srslte_resampler_fft_t* q, const cf_t* input,
 
       // Execute iFFT
       srslte_dft_run_guru_c(&q->ifft);
+    } else {
+      srslte_vec_cf_zero(q->out_buffer, q->ifft.size);
+    }
 
     // Add previous state
     srslte_vec_sum_ccc(q->out_buffer, q->state, q->out_buffer, q->state_len);
 
     // Copy output
+    if (output) {
       srslte_vec_cf_copy(&output[count / q->ratio], q->out_buffer, n / q->ratio);
+    }
 
     // Save current state
     q->state_len = q->ifft.size - n / q->ratio;