The _lut is being indexed by I + Q (16 bits = 65536 entries), however both samples can be processed independently, resulting in 8-bit LUT. Saves a bit of RAM and CPU cache.
diff --git a/lib/rtl/rtl_source_c.cc b/lib/rtl/rtl_source_c.cc index 93328b8..999ff9e 100644 --- a/lib/rtl/rtl_source_c.cc +++ b/lib/rtl/rtl_source_c.cc @@ -172,15 +172,8 @@ rtl_source_c::rtl_source_c (const std::string &args) _samp_avail = _buf_len / BYTES_PER_SAMPLE;
// create a lookup table for gr_complex values - for (unsigned int i = 0; i <= 0xffff; i++) { -#ifdef BOOST_LITTLE_ENDIAN - _lut.push_back( gr_complex( (float(i & 0xff) - 127.4f) * (1.0f/128.0f), - (float(i >> 8) - 127.4f) * (1.0f/128.0f) ) ); -#else // BOOST_BIG_ENDIAN - _lut.push_back( gr_complex( (float(i >> 8) - 127.4f) * (1.0f/128.0f), - (float(i & 0xff) - 127.4f) * (1.0f/128.0f) ) ); -#endif - } + for (unsigned int i = 0; i < 0x100; i++) + _lut.push_back((i - 127.4f) / 128.0f);
_dev = NULL; ret = rtlsdr_open( &_dev, dev_index ); @@ -230,11 +223,11 @@ rtl_source_c::rtl_source_c (const std::string &args)
set_if_gain( 24 ); /* preset to a reasonable default (non-GRC use case) */
- _buf = (unsigned short **) malloc(_buf_num * sizeof(unsigned short *)); + _buf = (unsigned char **)malloc(_buf_num * sizeof(unsigned char *));
if (_buf) { for(unsigned int i = 0; i < _buf_num; ++i) - _buf[i] = (unsigned short *) malloc(_buf_len); + _buf[i] = (unsigned char *)malloc(_buf_len); } }
@@ -348,10 +341,10 @@ int rtl_source_c::work( int noutput_items,
while (noutput_items && _buf_used) { const int nout = std::min(noutput_items, _samp_avail); - const unsigned short *buf = _buf[_buf_head] + _buf_offset; + const unsigned char *buf = _buf[_buf_head] + _buf_offset * 2;
for (int i = 0; i < nout; ++i) - *out++ = _lut[ *(buf + i) ]; + *out++ = gr_complex(_lut[buf[i * 2]], _lut[buf[i * 2 + 1]]);
noutput_items -= nout; _samp_avail -= nout; diff --git a/lib/rtl/rtl_source_c.h b/lib/rtl/rtl_source_c.h index 76de400..902b386 100644 --- a/lib/rtl/rtl_source_c.h +++ b/lib/rtl/rtl_source_c.h @@ -122,11 +122,11 @@ private: static void _rtlsdr_wait(rtl_source_c *obj); void rtlsdr_wait();
- std::vector<gr_complex> _lut; + std::vector<float> _lut;
rtlsdr_dev_t *_dev; gr::thread::thread _thread; - unsigned short **_buf; + unsigned char **_buf; unsigned int _buf_num; unsigned int _buf_len; unsigned int _buf_head;