Faster resampler

src/algorithms/libs/gps_sdr_signal_processing.cc

@@ -34,11 +34,15 @@
 #include <stdlib.h>
 #include <cmath>
 
+auto auxCeil = [](float x){ return static_cast<int>(static_cast<long>((x)+1)); };
 
 void gps_l1_ca_code_gen_complex(std::complex<float>* _dest, signed int _prn, unsigned int _chip_shift)
 {
-    bool G1[1023];
+
-    bool G2[1023];
+
+    const unsigned int _code_length = 1023;
+    bool G1[_code_length];
+    bool G2[_code_length];
     bool G1_register[10], G2_register[10];
     bool feedback1, feedback2;
     bool aux;
@@ -47,7 +51,7 @@ void gps_l1_ca_code_gen_complex(std::complex<float>* _dest, signed int _prn, uns
     signed int prn_idx;
 
     /* G2 Delays as defined in GPS-ISD-200D */
-    signed int delays[51] = {5 /*PRN1*/, 6, 7, 8, 17, 18, 139, 140, 141, 251, 252, 254 ,255, 256, 257, 258, 469, 470, 471, 472,
+    const signed int delays[51] = {5 /*PRN1*/, 6, 7, 8, 17, 18, 139, 140, 141, 251, 252, 254 ,255, 256, 257, 258, 469, 470, 471, 472,
             473, 474, 509, 512, 513, 514, 515, 516, 859, 860, 861, 862 /*PRN32*/,
             145 /*PRN120*/, 175, 52, 21, 237, 235, 886, 657, 634, 762,
             355, 1012, 176, 603, 130, 359, 595, 68, 386 /*PRN138*/};
@@ -73,7 +77,7 @@ void gps_l1_ca_code_gen_complex(std::complex<float>* _dest, signed int _prn, uns
         }
 
     /* Generate G1 & G2 Register */
-    for(lcv = 0; lcv < 1023; lcv++)
+    for(lcv = 0; lcv < _code_length; lcv++)
         {
             G1[lcv] = G1_register[0];
             G2[lcv] = G2_register[0];
@@ -92,14 +96,14 @@ void gps_l1_ca_code_gen_complex(std::complex<float>* _dest, signed int _prn, uns
         }
 
     /* Set the delay */
-    delay = 1023 - delays[prn_idx];
+    delay = _code_length - delays[prn_idx];
     delay += _chip_shift;
-    delay %= 1023;
+    delay %= _code_length;
 
     /* Generate PRN from G1 and G2 Registers */
-    for(lcv = 0; lcv < 1023; lcv++)
+    for(lcv = 0; lcv < _code_length; lcv++)
         {
-            aux = G1[(lcv +  _chip_shift) % 1023]^G2[delay];
+            aux = G1[(lcv + _chip_shift) % _code_length]^G2[delay];
             if(aux == true)
                 {
                     _dest[lcv] = std::complex<float>(1, 0);
@@ -109,7 +113,7 @@ void gps_l1_ca_code_gen_complex(std::complex<float>* _dest, signed int _prn, uns
                     _dest[lcv] = std::complex<float>(-1, 0);
                 }
             delay++;
-            delay %= 1023;
+            delay %= _code_length;
         }
 }
 
@@ -125,6 +129,7 @@ void gps_l1_ca_code_gen_complex_sampled(std::complex<float>* _dest, unsigned int
     signed int _samplesPerCode, _codeValueIndex;
     float _ts;
     float _tc;
+    float aux;
     const signed int _codeFreqBasis = 1023000; //Hz
     const signed int _codeLength = 1023;
 
@@ -145,7 +150,9 @@ void gps_l1_ca_code_gen_complex_sampled(std::complex<float>* _dest, unsigned int
             // number of samples per millisecond (because one C/A code period is one
             // millisecond).
 
-            _codeValueIndex = ceil((_ts * ((float)i + 1)) / _tc) - 1;
+            // _codeValueIndex = ceil((_ts * ((float)i + 1)) / _tc) - 1;
+            aux = (_ts * (i + 1)) / _tc;   
+            _codeValueIndex = auxCeil( aux ) - 1;
 
             //--- Make the digitized version of the C/A code -----------------------
             // The "upsampled" code is made by selecting values form the CA code
@@ -163,6 +170,3 @@ void gps_l1_ca_code_gen_complex_sampled(std::complex<float>* _dest, unsigned int
         }
 }
 
-
-
-

src/tests/arithmetic/code_generation_test.cc

@@ -78,3 +78,53 @@ TEST(CodeGenGPSL1_Test, CodeGeneration)
         }
     delete _dest2; */
 }
+
+
+
+
+TEST(CodeGenGPSL1Sampled_Test, CodeGeneration)
+{
+    signed int _prn = 1;
+    unsigned int _chip_shift = 4;
+    int _fs = 8000000;
+    const signed int _codeFreqBasis = 1023000; //Hz
+    const signed int _codeLength = 1023;
+    int _samplesPerCode = round(_fs / (_codeFreqBasis / _codeLength));
+    std::complex<float>* _dest = new std::complex<float>[_samplesPerCode];
+
+    int iterations = 10000;
+
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    long long int begin = tv.tv_sec * 1000000 + tv.tv_usec;
+
+    for(int i = 0; i < iterations; i++)
+        {
+            gps_l1_ca_code_gen_complex_sampled( _dest,  _prn, _fs, _chip_shift);
+        }
+
+    gettimeofday(&tv, NULL);
+    long long int end = tv.tv_sec * 1000000 + tv.tv_usec;
+    ASSERT_LE(0, end - begin);
+    std::cout << "Generation completed in " << (end - begin) << " microseconds" << std::endl;
+    delete[] _dest;
+
+    /* std::complex<float>* _dest2 = new std::complex<float>[_samplesPerCode];
+    gettimeofday(&tv, NULL);
+    long long int begin2 = tv.tv_sec * 1000000 + tv.tv_usec;
+
+    for(int i = 0; i < iterations; i++)
+        {
+            gps_l1_ca_code_gen_complex_sampled2( _dest2,  _prn, _fs, _chip_shift);
+        }
+
+    gettimeofday(&tv, NULL);
+    long long int end2 = tv.tv_sec * 1000000 + tv.tv_usec;
+    std::cout << "Generation completed in " << (end2 - begin2) << " microseconds  (New)" << std::endl;
+
+    for (int j=0; j<_samplesPerCode;j++)
+        {
+            if(_dest[j] != _dest2[j]) std::cout << "Error!" << std::endl;
+        }
+    delete[] _dest2; */
+}