From 9542e8a8f9aa8c033e110b26fb719d6ebb123fab Mon Sep 17 00:00:00 2001
From: Florian Kaltenberger <florian.kaltenberger@eurecom.fr>
Date: Thu, 8 Jun 2017 09:22:30 +0200
Subject: [PATCH] alternative version of dlsch_channel_level not needing
 floating point

---
 .../PHY/LTE_TRANSPORT/dlsch_demodulation.c    | 11 ++++------
 openair1/PHY/TOOLS/defs.h                     |  3 +++
 openair1/PHY/TOOLS/log2_approx.c              | 20 +++++++++++++++++++
 3 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/openair1/PHY/LTE_TRANSPORT/dlsch_demodulation.c b/openair1/PHY/LTE_TRANSPORT/dlsch_demodulation.c
index e6d2ec301f..f5281beffc 100644
--- a/openair1/PHY/LTE_TRANSPORT/dlsch_demodulation.c
+++ b/openair1/PHY/LTE_TRANSPORT/dlsch_demodulation.c
@@ -3389,11 +3389,9 @@ void dlsch_channel_level(int **dl_ch_estimates_ext,
     nre=12;
 
   //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);
+  int16_t x = factor2(nb_rb*nre);
+  int16_t y = (nb_rb*nre)/(1<<x);
+  printf("nb_rb*nre = %d = %d * 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++) {
@@ -3432,8 +3430,7 @@ void dlsch_channel_level(int **dl_ch_estimates_ext,
       avg[(aatx<<1)+aarx] =  (((int32_t*)&avg128D)[0] +
 			      ((int32_t*)&avg128D)[1] +
 			      ((int32_t*)&avg128D)[2] +
-			      ((int32_t*)&avg128D)[3]);
-      avg[(aatx<<1)+aarx] = (int32_t) ((float) avg[(aatx<<1)+aarx]/y);
+			      ((int32_t*)&avg128D)[3])/y;
       printf("Channel level : %d\n",avg[(aatx<<1)+aarx]);
     }
 
diff --git a/openair1/PHY/TOOLS/defs.h b/openair1/PHY/TOOLS/defs.h
index 542b8edba5..a90a8b718c 100644
--- a/openair1/PHY/TOOLS/defs.h
+++ b/openair1/PHY/TOOLS/defs.h
@@ -338,6 +338,9 @@ uint8_t log2_approx64(unsigned long long int x);
 int16_t invSqrt(int16_t x);
 uint32_t angle(struct complex16 perrror);
 
+/// computes the number of factors 2 in x
+unsigned char factor2(unsigned int x);
+
 /*!\fn int32_t phy_phase_compensation_top (uint32_t pilot_type, uint32_t initial_pilot,
         uint32_t last_pilot, int32_t ignore_prefix);
 Compensate the phase rotation of the RF. WARNING: This function is currently unused. It has not been tested!
diff --git a/openair1/PHY/TOOLS/log2_approx.c b/openair1/PHY/TOOLS/log2_approx.c
index 0317a97d2f..bd4d5d04ab 100644
--- a/openair1/PHY/TOOLS/log2_approx.c
+++ b/openair1/PHY/TOOLS/log2_approx.c
@@ -37,6 +37,26 @@ unsigned char log2_approx(unsigned int x)
   return(l2);
 }
 
+unsigned char factor2(unsigned int x)
+{
+
+  int i;
+  unsigned char l2;
+
+  l2=0;
+
+  for (i=0; i<31; i++)
+    if ((x&(1<<i)) != 0)
+      break;
+
+  l2 = i;
+
+  //printf("factor2(%d) = %d\n",x,l2);
+  return(l2);
+}
+
+
+
 unsigned char log2_approx64(unsigned long long int x)
 {