24 Aug
2016
24 Aug
'16
11:53 p.m.
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;