a new proposal for the dlsch_channel_level function

openair1/PHY/LTE_TRANSPORT/dlsch_demodulation.c

@@ -3377,7 +3377,7 @@ void dlsch_channel_level(int **dl_ch_estimates_ext,
 
   short rb;
   unsigned char aatx,aarx,nre=12,symbol_mod;
-  __m128i *dl_ch128, avg128D, coeff128;
+  __m128i *dl_ch128, avg128D;
 
   symbol_mod = (symbol>=(7-frame_parms->Ncp)) ? symbol-(7-frame_parms->Ncp) : symbol;
 
@@ -3388,11 +3388,12 @@ void dlsch_channel_level(int **dl_ch_estimates_ext,
   else
     nre=12;
 
-  double one_over_nb_re = 0.0;
-  one_over_nb_re = 1/((double)(nb_rb*nre));
-  int16_t one_over_nb_re_q1_15 = (int16_t)(one_over_nb_re * (double)(1<<15) );
-  coeff128 = _mm_set_epi16(one_over_nb_re_q1_15,one_over_nb_re_q1_15,one_over_nb_re_q1_15,one_over_nb_re_q1_15,
-                            one_over_nb_re_q1_15,one_over_nb_re_q1_15,one_over_nb_re_q1_15,one_over_nb_re_q1_15);
+  //nb_rb*nre = y * 2^x
+  int16_t x = log2_approx(nb_rb*nre)-1;
+  //int16_t one_over_y_q15 = (int16_t)((1<<((int32_t)x+15))/((int32_t)nb_rb*(int32_t)nre));
+  float y = (float)(nb_rb*nre)/(float)(1<<x);
+  //printf("1/(nb_rb*nre) = 1/%d = %d*2^(-15) * 2^(-%d)\n",nb_rb*nre,one_over_y_q15,x);
+  printf("nb_rb*nre = %d = %f * 2^(%d)\n",nb_rb*nre,y,x);
 
   for (aatx=0; aatx<frame_parms->nb_antenna_ports_eNB; aatx++)
     for (aarx=0; aarx<frame_parms->nb_antennas_rx; aarx++) {
@@ -3405,14 +3406,18 @@ void dlsch_channel_level(int **dl_ch_estimates_ext,
       for (rb=0;rb<nb_rb;rb++) {
         //      printf("rb %d : ",rb);
         //      print_shorts("ch",&dl_ch128[0]);
-        avg128D = _mm_add_epi32(avg128D,_mm_madd_epi16(dl_ch128[0],_mm_srai_epi16(_mm_mulhi_epi16(dl_ch128[0], coeff128),15)));
-        avg128D = _mm_add_epi32(avg128D,_mm_madd_epi16(dl_ch128[1],_mm_srai_epi16(_mm_mulhi_epi16(dl_ch128[1], coeff128),15)));
+	avg128D = _mm_add_epi32(avg128D,_mm_srai_epi16(_mm_madd_epi16(dl_ch128[0],dl_ch128[0]),x));
+	avg128D = _mm_add_epi32(avg128D,_mm_srai_epi16(_mm_madd_epi16(dl_ch128[1],dl_ch128[1]),x));
+
+        //avg128D = _mm_add_epi32(avg128D,_mm_madd_epi16(dl_ch128[0],_mm_srai_epi16(_mm_mulhi_epi16(dl_ch128[0], coeff128),15)));
+        //avg128D = _mm_add_epi32(avg128D,_mm_madd_epi16(dl_ch128[1],_mm_srai_epi16(_mm_mulhi_epi16(dl_ch128[1], coeff128),15)));
 
         if (((symbol_mod == 0) || (symbol_mod == (frame_parms->Ncp-1)))&&(frame_parms->mode1_flag==0)) {
           dl_ch128+=2;
         }
         else {
-          avg128D = _mm_add_epi32(avg128D,_mm_madd_epi16(dl_ch128[2],_mm_srai_epi16(_mm_mulhi_epi16(dl_ch128[2], coeff128),15)));
+	  avg128D = _mm_add_epi32(avg128D,_mm_srai_epi16(_mm_madd_epi16(dl_ch128[2],dl_ch128[2]),x));
+          //avg128D = _mm_add_epi32(avg128D,_mm_madd_epi16(dl_ch128[2],_mm_srai_epi16(_mm_mulhi_epi16(dl_ch128[2], coeff128),15)));
           dl_ch128+=3;
         }
         /*
@@ -3424,11 +3429,12 @@ void dlsch_channel_level(int **dl_ch_estimates_ext,
         */
       }
 
-      avg[(aatx<<1)+aarx] =(((int32_t*)&avg128D)[0] +
+      avg[(aatx<<1)+aarx] =  (((int32_t*)&avg128D)[0] +
 			      ((int32_t*)&avg128D)[1] +
 			      ((int32_t*)&avg128D)[2] +
 			      ((int32_t*)&avg128D)[3]);
-                //  printf("Channel level : %d\n",avg[(aatx<<1)+aarx]);
+      avg[(aatx<<1)+aarx] = (int32_t) ((float) avg[(aatx<<1)+aarx]/y);
+      printf("Channel level : %d\n",avg[(aatx<<1)+aarx]);
     }
 
   _mm_empty();