Do all time calculations in uint64_t

This prevents loss of precision that occurs with double-precision floats if
timestamps become very large. Timestamps are already large if they contain a
UNIX time value (requires 60 bits; double has 53 bit resolution).

impl/src/main.c

@@ -50,7 +50,7 @@
 static int  m_tunfd = -1;
 static bool m_running = true;
 
-static double next_tx_switch_time = 0.0;
+static uint64_t next_tx_switch_time = 0;
 
 static rx_stats_t m_rx_stats;
 
@@ -71,7 +71,7 @@ static void signal_handler(int signal, siginfo_t *info, void *ctx)
 
 static void block_tx_for(unsigned offset_ms)
 {
-	next_tx_switch_time = get_hires_time() + (double)offset_ms * 0.001;
+	next_tx_switch_time = get_hires_time() + HRTIME_MS(offset_ms);
 }
 
 void print_complex_array(const char *varname, float complex const *array, size_t len)
@@ -186,7 +186,7 @@ int main(int argc, char **argv)
 
 	bool on_air = true;
 
-	srand((int)(get_hires_time() * 1e6));
+	srand(get_hires_time());
 
 	// ** Initialize **
 
@@ -233,18 +233,18 @@ int main(int argc, char **argv)
 
 	unsigned rx_retries = 0;
 
-	double old = get_hires_time();
+	uint64_t old = get_hires_time();
 	size_t total_samples = 0;
-	double next_stats_print_time = old + 0.5;
+	uint64_t next_stats_print_time = old + HRTIME_MS(500);
 
-	double retransmit_time = 0.0;
+	uint64_t retransmit_time = 0;
 
 	while(m_running) {
-		double now = get_hires_time();
+		uint64_t now = get_hires_time();
 
-		if(retransmit_time != 0.0 && now >= retransmit_time) {
+		if(retransmit_time != 0 && now >= retransmit_time) {
 			LOG(LVL_INFO, "Retransmit triggered.");
-			retransmit_time = 0.0;
+			retransmit_time = 0;
 			layer2_tx_restart(&l2tx);
 		}
 
@@ -325,7 +325,7 @@ int main(int argc, char **argv)
 				RESULT_CHECK(sdr_start_rx(&sdr));
 				on_air = false;
 
-				retransmit_time = get_hires_time() + 1.0 + 1.0 * rand() / RAND_MAX;
+				retransmit_time = get_hires_time() + HRTIME_SEC(1) + HRTIME_SEC(1.0 * rand() / RAND_MAX);
 
 				block_tx_for(TX_SWITCH_BACKOFF_AFTER_RX_ON);
 			}
@@ -360,9 +360,9 @@ int main(int argc, char **argv)
 
 			total_samples += n_rf_samples;
 
-			double new = get_hires_time();
+			uint64_t new = get_hires_time();
 			if(new >= next_stats_print_time) {
-				double rate = total_samples / (new - old);
+				double rate = total_samples * 1e9 / (new - old);
 				LOG(LVL_INFO, "\nEstimated rate: %.3f MS/s", rate / 1e6);
 				LOG(LVL_INFO, "Receiver statistics:");
 				LOG(LVL_INFO, "  Preambles found:    %8zd", m_rx_stats.preambles_found);

impl/src/sdr/sdr.c

@@ -99,9 +99,9 @@ static int tx_callback(hackrf_transfer *transfer)
 		return HACKRF_ERROR_OTHER;
 	}
 
-	if(sdr_ctx->tx_start_time == 0.0) {
+	if(sdr_ctx->tx_start_time == 0) {
 		sdr_ctx->tx_start_time = get_hires_time();
-		sdr_ctx->tx_duration = 10e-3; // give a little headroom
+		sdr_ctx->tx_duration = HRTIME_MS(10); // give a little headroom
 		LOG(LVL_INFO, "TX time tracking reset: start = %.3f.", sdr_ctx->tx_start_time);
 	}
 
@@ -112,7 +112,7 @@ static int tx_callback(hackrf_transfer *transfer)
 
 	if(samples_read != 0) {
 		// only add time if any actual samples were transmitted
-		sdr_ctx->tx_duration += (double)samples_requested / SDR_TX_SAMPLING_RATE;
+		sdr_ctx->tx_duration += HRTIME_SEC((double)samples_requested / SDR_TX_SAMPLING_RATE);
 	}
 
 	LOG(LVL_DEBUG, "copied %u samples to HackRF.", samples_read);
@@ -377,8 +377,8 @@ result_t sdr_flush_tx_buffer(sdr_ctx_t *ctx)
 			return 0;
 		}
 
-		double now = get_hires_time();
+		uint64_t now = get_hires_time();
-		double end = ctx->tx_start_time + ctx->tx_duration;
+		uint64_t end = ctx->tx_start_time + ctx->tx_duration;
 
 		if(sem_post(&ctx->buf_sem) < 0) {
 			LOG(LVL_ERR, "sem_post: %s", strerror(errno));

impl/src/utils.c

@@ -76,11 +76,23 @@ err_close:
 	return false;
 }
 
-double get_hires_time(void)
+uint64_t get_hires_time(void)
 {
 	struct timespec clk;
 	clock_gettime(CLOCK_MONOTONIC, &clk);
-	return clk.tv_sec + 1e-9 * clk.tv_nsec;
+	return clk.tv_sec * 1000000000ULL + (uint64_t)clk.tv_nsec;
+}
+
+void sleep_until(uint64_t hires_time)
+{
+	struct timespec tv;
+	int ret;
+
+	tv.tv_sec = hires_time / 1000000000ULL;
+	tv.tv_nsec = hires_time % 1000000000ULL;
+	do {
+		ret = clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &tv, NULL);
+	} while(ret == EINTR);
 }
 
 void fsleep(double d)
@@ -93,18 +105,6 @@ void fsleep(double d)
 	nanosleep(&ts, NULL);
 }
 
-void sleep_until(double hires_time)
-{
-	struct timespec tv;
-	int ret;
-
-	tv.tv_sec = hires_time;
-	tv.tv_nsec = (uint64_t)(1e9 * hires_time) % 1000000000;
-	do {
-		ret = clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &tv, NULL);
-	} while(ret == EINTR);
-}
-
 void hexdump(const uint8_t *data, size_t len)
 {
 	static const char lut[16] = "0123456789ABCDEF";

impl/src/utils.h

@@ -11,6 +11,10 @@
 #include <stdbool.h>
 #include <liquid/liquid.h>
 
+#define HRTIME_US(x) ((uint64_t)(1000ULL * (x)))
+#define HRTIME_MS(x) ((uint64_t)(1000000ULL * (x)))
+#define HRTIME_SEC(x) ((uint64_t)(1000000000ULL * (x)))
+
 /*! Dump a array of complex numbers.
  *
  * \param data      Pointer to the data to dump.
@@ -30,9 +34,26 @@ bool dump_array_cf(const float complex *data, size_t n, float T, const char *fil
  */
 bool dump_array_f(const float *data, size_t n, float T, const char *filename);
 
-void sleep_until(double hires_time);
+
+/*! Sleep until the given absolute timestamp in ns.
+ *
+ * The current timestamp can be retrieved using \ref get_hires_time().
+ *
+ * \param hires_time     The resume timestamp in ns.
+ */
+void sleep_until(uint64_t hires_time);
+
+
+/*! Returns the current high-resulution timestamp.
+ *
+ * This timestamp comes from the CLOCK_MONOTONIC source and has no defined relation to the wall-clock time. It can be used to calculate intervals, though.
+ *
+ * \returns A timestamp in nanosecond resolution.
+ */
+uint64_t get_hires_time(void);
+
+
 void fsleep(double d);
-double get_hires_time(void);
 
 void hexdump(const uint8_t *data, size_t len);
 

impl/test/layer2_over_udp/l2udptest_client.c

@@ -50,7 +50,7 @@ static bool m_running = true;
 
 static int m_bcast_sock = -1;
 
-static double next_tx_switch_time = 0.0;
+static uint64_t next_tx_switch_time = 0;
 
 static rx_stats_t m_rx_stats;
 
@@ -69,7 +69,7 @@ static void signal_handler(int signal, siginfo_t *info, void *ctx)
 
 static void block_tx_for(unsigned offset_ms)
 {
-	next_tx_switch_time = get_hires_time() + (double)offset_ms * 0.001;
+	next_tx_switch_time = get_hires_time() + HRTIME_MS(offset_ms);
 }
 
 
@@ -143,7 +143,7 @@ int main(int argc, char **argv)
 
 	bool on_air = true;
 
-	srand((int)(get_hires_time() * 1e6));
+	srand(get_hires_time());
 
 	// ** Initialize **
 
@@ -218,18 +218,18 @@ int main(int argc, char **argv)
 	pfd_bcast.fd = m_bcast_sock;
 	pfd_bcast.events = POLLIN;
 
-	double old = get_hires_time();
+	uint64_t old = get_hires_time();
 	size_t total_bytes = 0;
-	double next_stats_print_time = old + 0.5;
+	uint64_t next_stats_print_time = old + HRTIME_MS(500);
 
-	double retransmit_time = 0.0;
+	uint64_t retransmit_time = 0;
 
 	while(m_running) {
-		double now = get_hires_time();
+		uint64_t now = get_hires_time();
 
-		if(retransmit_time != 0.0 && now >= retransmit_time) {
+		if(retransmit_time != 0 && now >= retransmit_time) {
 			LOG(LVL_INFO, "Retransmit triggered.");
-			retransmit_time = 0.0;
+			retransmit_time = 0;
 			connection_restart_tx(&l2conn);
 		}
 
@@ -301,7 +301,7 @@ int main(int argc, char **argv)
 				LOG(LVL_INFO, "TX -> RX");
 				on_air = false;
 
-				retransmit_time = get_hires_time() + 1.0 + 1.0 * rand() / RAND_MAX;
+				retransmit_time = get_hires_time() + HRTIME_SEC(1) + HRTIME_SEC(1.0 * rand() / RAND_MAX);
 
 				block_tx_for(TX_SWITCH_BACKOFF_AFTER_RX_ON);
 			}
@@ -334,9 +334,9 @@ int main(int argc, char **argv)
 
 			total_bytes += ret;
 
-			double new = get_hires_time();
+			uint64_t new = get_hires_time();
 			if(new >= next_stats_print_time) {
-				double rate = total_bytes / (new - old);
+				double rate = total_bytes * 1e9 / (new - old);
 				LOG(LVL_INFO, "\nEstimated rate: %.3f kB/s", rate / 1e3);
 				LOG(LVL_INFO, "Receiver statistics:");
 				LOG(LVL_INFO, "  Preambles found:    %8zd", m_rx_stats.preambles_found);
@@ -346,7 +346,7 @@ int main(int argc, char **argv)
 						m_rx_stats.header_errors, m_rx_stats.header_errors * 100.0f / m_rx_stats.preambles_found);
 				LOG(LVL_INFO, "  Failed decodes:     %8zd (%6.2f %%)",
 						m_rx_stats.failed_decodes, m_rx_stats.failed_decodes * 100.0f / m_rx_stats.preambles_found);
-				next_stats_print_time += 0.5;
+				next_stats_print_time += HRTIME_MS(500);
 
 				total_bytes = 0;
 				old = new;

impl/test/layer2_over_udp/l2udptest_digipeater.c

@@ -50,7 +50,7 @@ static bool m_running = true;
 
 static int m_bcast_sock = -1;
 
-static double next_tx_switch_time = 0.0;
+static uint64_t next_tx_switch_time = 0;
 
 static rx_stats_t m_rx_stats;
 
@@ -69,7 +69,7 @@ static void signal_handler(int signal, siginfo_t *info, void *ctx)
 
 static void block_tx_for(unsigned offset_ms)
 {
-	next_tx_switch_time = get_hires_time() + (double)offset_ms * 0.001;
+	next_tx_switch_time = get_hires_time() + HRTIME_MS(offset_ms);
 }
 
 
@@ -143,7 +143,7 @@ int main(int argc, char **argv)
 
 	bool on_air = true;
 
-	srand((int)(get_hires_time() * 1e6));
+	srand(get_hires_time());
 
 	// ** Initialize **
 
@@ -218,18 +218,18 @@ int main(int argc, char **argv)
 	pfd_bcast.fd = m_bcast_sock;
 	pfd_bcast.events = POLLIN;
 
-	double old = get_hires_time();
+	uint64_t old = get_hires_time();
 	size_t total_bytes = 0;
-	double next_stats_print_time = old + 0.5;
+	uint64_t next_stats_print_time = old + HRTIME_MS(500);
 
-	double retransmit_time = 0.0;
+	uint64_t retransmit_time = 0;
 
 	while(m_running) {
-		double now = get_hires_time();
+		uint64_t now = get_hires_time();
 
-		if(retransmit_time != 0.0 && now >= retransmit_time) {
+		if(retransmit_time != 0 && now >= retransmit_time) {
 			LOG(LVL_INFO, "Retransmit triggered.");
-			retransmit_time = 0.0;
+			retransmit_time = 0;
 			connection_restart_tx(&l2conn);
 		}
 
@@ -301,7 +301,7 @@ int main(int argc, char **argv)
 				LOG(LVL_INFO, "TX -> RX");
 				on_air = false;
 
-				retransmit_time = get_hires_time() + 1.0 + 1.0 * rand() / RAND_MAX;
+				retransmit_time = get_hires_time() + HRTIME_SEC(1) + HRTIME_SEC(1.0 * rand() / RAND_MAX);
 
 				block_tx_for(TX_SWITCH_BACKOFF_AFTER_RX_ON);
 			}
@@ -334,9 +334,9 @@ int main(int argc, char **argv)
 
 			total_bytes += ret;
 
-			double new = get_hires_time();
+			uint64_t new = get_hires_time();
 			if(new >= next_stats_print_time) {
-				double rate = total_bytes / (new - old);
+				double rate = total_bytes * 1e9 / (new - old);
 				LOG(LVL_INFO, "\nEstimated rate: %.3f kB/s", rate / 1e3);
 				LOG(LVL_INFO, "Receiver statistics:");
 				LOG(LVL_INFO, "  Preambles found:    %8zd", m_rx_stats.preambles_found);
@@ -346,7 +346,7 @@ int main(int argc, char **argv)
 						m_rx_stats.header_errors, m_rx_stats.header_errors * 100.0f / m_rx_stats.preambles_found);
 				LOG(LVL_INFO, "  Failed decodes:     %8zd (%6.2f %%)",
 						m_rx_stats.failed_decodes, m_rx_stats.failed_decodes * 100.0f / m_rx_stats.preambles_found);
-				next_stats_print_time += 0.5;
+				next_stats_print_time += HRTIME_MS(500);
 
 				total_bytes = 0;
 				old = new;