add simple cross-correlation method

- implements a cross-correlation that takes the complex conjugate
  of one of the input signals (filter)
- the fft of this input signal is only computed once

lib/include/srslte/phy/utils/convolution.h

@@ -61,10 +61,14 @@ SRSLTE_API int srslte_conv_fft_cc_replan(srslte_conv_fft_cc_t *q,
 
 SRSLTE_API void srslte_conv_fft_cc_free(srslte_conv_fft_cc_t *q);
 
-SRSLTE_API uint32_t srslte_conv_fft_cc_run(srslte_conv_fft_cc_t *q,
-                                           const cf_t *input,
-                                           const cf_t *filter,
-                                           cf_t *output);
+SRSLTE_API uint32_t srslte_corr_fft_cc_run(srslte_conv_fft_cc_t* q, cf_t* input, cf_t* filter, cf_t* output);
+
+SRSLTE_API uint32_t srslte_corr_fft_cc_run_opt(srslte_conv_fft_cc_t* q, cf_t* input, cf_t* filter, cf_t* output);
+
+SRSLTE_API uint32_t srslte_conv_fft_cc_run(srslte_conv_fft_cc_t* q,
+                                           const cf_t*           input,
+                                           const cf_t*           filter,
+                                           cf_t*                 output);
 
 SRSLTE_API uint32_t srslte_conv_fft_cc_run_opt(srslte_conv_fft_cc_t *q,
                                                const cf_t *input,

lib/src/phy/utils/convolution.c

@@ -127,6 +127,20 @@ uint32_t srslte_conv_fft_cc_run(srslte_conv_fft_cc_t *q, const cf_t *input, cons
 
 }
 
+uint32_t srslte_corr_fft_cc_run_opt(srslte_conv_fft_cc_t* q, cf_t* input, cf_t* filter, cf_t* output)
+{
+  srslte_dft_run_c(&q->input_plan, input, q->input_fft);
+  srslte_vec_prod_conj_ccc(q->input_fft, q->filter_fft, q->output_fft, q->output_len);
+  srslte_dft_run_c(&q->output_plan, q->output_fft, output);
+  return (q->output_len - 1);
+}
+
+uint32_t srslte_corr_fft_cc_run(srslte_conv_fft_cc_t* q, cf_t* input, cf_t* filter, cf_t* output)
+{
+  srslte_dft_run_c(&q->filter_plan, filter, q->filter_fft);
+  return srslte_corr_fft_cc_run_opt(q, input, q->filter_fft, output);
+}
+
 uint32_t srslte_conv_cc(const cf_t *input, const cf_t *filter, cf_t *output, uint32_t input_len, uint32_t filter_len) {
   uint32_t i;
   uint32_t M = filter_len;