smooth: Use integers rather than floats to store tme

include/smooth.h

@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <stdint.h>
+
 /*
  * This is an exponential smoothing filter with a time constant.
  *
@@ -27,7 +29,7 @@
 struct smooth {
 	double time_constant;
 
-	double last_time;
+	uint64_t last_time;
 	double last_result;
 };
 

include/time-util.h

@@ -1,11 +1,11 @@
 #include <time.h>
 #include <stdint.h>
 
-static inline double gettime_s(void)
+static inline uint64_t gettime_us(void)
 {
 	struct timespec ts = { 0 };
 	clock_gettime(CLOCK_MONOTONIC, &ts);
-	return (double)ts.tv_sec + (double)ts.tv_nsec / 1.0e-9;
+	return ts.tv_sec * 1000000ULL + (double)ts.tv_nsec / 1000ULL;
 }
 
 static inline uint32_t gettime_ms(void)

src/smooth.c

@@ -21,8 +21,8 @@
 
 double smooth(struct smooth* self, double input)
 {
-	double now = gettime_s();
-	double dt = now - self->last_time;
+	uint64_t now = gettime_us();
+	double dt = (now - self->last_time) * 1.0e-6;
 	self->last_time = now;
 
 	double factor = 1.0 - exp(-dt / self->time_constant);