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symbol.c
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symbol.c
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/*
* This file contains implementations for some basic symbol streams,
*/
#include <stdint.h>
#include "symbol.h"
#include "sample.h"
struct iq bpsk_constellation[] = {
{
.i = -1.0f,
.q = 0.0f,
},
{
.i = 1.0f,
.q = 0.0f,
}
};
static int bpsk_stream_len(struct symbol_stream *ss)
{
struct bpsk_stream *bs;
bs = to_bpsk_stream(ss);
return bs->bits - bs->bit_idx;
}
static int bpsk_get_symbol(struct symbol_stream *ss, struct iq *sym)
{
u8 bit;
int idx;
u8 shift;
struct bpsk_stream *bs;
bs = to_bpsk_stream(ss);
if (bs->bit_idx >= bs->bits) {
return 0; /* stream drained */
}
/*
* TODO(mgyenik) doing these calculations each time is wasteful. We can
* speed up the implementation if needed by caching some of this
* intermediate state in the bpsk_stream struct and just updating it.
*/
idx = bs->bit_idx >> 3;
shift = bs->bit_idx & 0x7;
shift = 7 - shift;
bit = bs->data[idx] >> shift;
bit &= 0x1;
*sym = bpsk_constellation[bit];
bs->bit_idx++;
return 1;
}
int init_bpsk_stream(struct bpsk_stream *bs, u8 *data, int n)
{
bs->bit_idx = 0;
bs->len = n;
bs->bits = n*8;
bs->data = data;
bs->stream.get_symbol = bpsk_get_symbol;
bs->stream.len = bpsk_stream_len;
return 0;
}
/* Below is QPSK, very similar... */
struct iq qpsk_constellation[] = {
{
.i = -SQRT2_INV,
.q = -SQRT2_INV,
},
{
.i = -SQRT2_INV,
.q = SQRT2_INV,
},
{
.i = SQRT2_INV,
.q = -SQRT2_INV,
},
{
.i = SQRT2_INV,
.q = SQRT2_INV,
},
};
static int qpsk_stream_len(struct symbol_stream *ss)
{
struct qpsk_stream *qs;
qs = to_qpsk_stream(ss);
return (qs->bits - qs->bit_idx)/2;
}
static int qpsk_get_symbol(struct symbol_stream *ss, struct iq *sym)
{
u8 bits;
int idx;
u8 shift;
struct qpsk_stream *qs;
qs = to_qpsk_stream(ss);
if (qs->bit_idx >= qs->bits) {
return 0; /* stream drained */
}
/*
* TODO(mgyenik) doing these calculations each time is wasteful. We can
* speed up the implementation if needed by caching some of this
* intermediate state in the bpsk_stream struct and just updating it.
*/
idx = qs->bit_idx >> 3;
shift = qs->bit_idx & 0x7;
shift = 6 - shift;
bits = qs->data[idx] >> shift;
bits &= 0x3;
*sym = qpsk_constellation[bits];
qs->bit_idx += 2;
return 1;
}
int init_qpsk_stream(struct qpsk_stream *qs, u8 *data, int n)
{
qs->bit_idx = 0;
qs->len = n;
qs->bits = n*8;
qs->data = data;
qs->stream.get_symbol = qpsk_get_symbol;
qs->stream.len = qpsk_stream_len;
return 0;
}
static int sample_hold_len(struct symbol_stream *ss)
{
int orig_len;
struct sample_hold *sh;
sh = to_sample_hold(ss);
orig_len = sh->orig_stream->len(sh->orig_stream);
return sh->hold*orig_len - sh->count;
}
static int get_sample_hold(struct symbol_stream *ss, struct iq *sym)
{
struct sample_hold *sh;
sh = to_sample_hold(ss);
if (sh->count < sh->hold) {
*sym = sh->current;
sh->count++;
} else {
if(!sh->orig_stream->get_symbol(sh->orig_stream, &sh->current)) {
return 0; /* stream drained */
}
sh->count = 0;
*sym = sh->current;
}
return 1;
}
int init_sample_hold(struct sample_hold *sh, struct symbol_stream *ss, int hold_count)
{
sh->hold = hold_count;
sh->orig_stream = ss;
sh->count = 0;
sh->stream.get_symbol = get_sample_hold;
sh->stream.len = sample_hold_len;
return 0;
}