RTL-SDR: convert _lut to float[] to reduce size by a factor of 256

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.
laforge/debian
Krzysztof Halasa 6 years ago committed by Dimitri Stolnikov
parent 5ecfa255d2
commit 33a8d1c2ae
  1. 19
      lib/rtl/rtl_source_c.cc
  2. 4
      lib/rtl/rtl_source_c.h

@ -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;

@ -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;

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