hamnet70/impl/src/correlator.c

#include <stdio.h>
#include <string.h>
#include <malloc.h>

#include "correlator.h"

bool correlator_init(correlator_ctx_t *ctx, const float complex *search_seq, size_t nsymbols)
{
	// copy arguments and initialize variables
	ctx->search_sequence_len = nsymbols;

	ctx->input_history = NULL;
	ctx->search_sequence = NULL;

	ctx->history_ptr = 0;

	// Determine the smallest power of two greater than nsymbols
	ctx->buffer_size = 1;
	while(nsymbols > 0) {
		ctx->buffer_size <<= 1;
		nsymbols >>= 1;
	}

	// If buffer_size = 0b1000, then buffer_size_mask=0b0111
	ctx->buffer_size_mask = ctx->buffer_size - 1;

	// Allocate the buffers
	ctx->input_history = malloc(ctx->buffer_size * sizeof(ctx->input_history[0]));
	if(!ctx->input_history) {
		fprintf(stderr, "correlator: malloc() failed!\n");
		goto fail;
	}

	ctx->search_sequence = malloc(ctx->buffer_size * sizeof(ctx->search_sequence[0]));
	if(!ctx->search_sequence) {
		fprintf(stderr, "correlator: malloc() failed!\n");
		goto fail;
	}

	// Clear the history buffer
	memset(ctx->input_history, 0, ctx->buffer_size * sizeof(ctx->input_history[0]));

	// Prepare the search sequence.
	// The complex values are conjugated in the process.
	for(size_t i = 0; i < ctx->search_sequence_len; i++) {
		ctx->search_sequence[i] = conjf(search_seq[i]);
	}

	// Success!
	return true;

fail:
	correlator_free(ctx);
	return false;
}


void correlator_free(correlator_ctx_t *ctx)
{
	if(ctx->input_history) {
		free(ctx->input_history);
		ctx->input_history = NULL;
	}

	if(ctx->search_sequence) {
		free(ctx->search_sequence);
		ctx->input_history = NULL;
	}

	ctx->buffer_size = 0;
	ctx->search_sequence_len = 0;
}


float complex correlator_step(correlator_ctx_t *ctx, float complex sample)
{
	float complex result = 0;

	// increment and wrap the history pointer
	ctx->history_ptr++;
	ctx->history_ptr &= ctx->buffer_size_mask;

	// copy the input sample to the history
	ctx->input_history[ctx->history_ptr] = sample;

	size_t n = (ctx->history_ptr - ctx->search_sequence_len + 1) & ctx->buffer_size_mask;

	// calculate the correlation
	for(size_t m = 0; m < ctx->search_sequence_len; m++) {
		size_t nm = (n + m) & ctx->buffer_size_mask;

		result += ctx->search_sequence[m] * ctx->input_history[nm];
	}

	return result;
}


void correlator_get_input_history(correlator_ctx_t *ctx, float complex *history)
{
	size_t n = (ctx->history_ptr - ctx->search_sequence_len + 1) & ctx->buffer_size_mask;

	for(size_t m = 0; m < ctx->search_sequence_len; m++) {
		size_t nm = (n + m) & ctx->buffer_size_mask;
		history[m] = ctx->input_history[nm];
	}
}


const float complex* correlator_get_conj_search_sequence(correlator_ctx_t *ctx)
{
	return ctx->search_sequence;
}