[sigrokproject#71] Fix rounding issues that make the tests fail

pv/util.cpp

@@ -199,11 +199,21 @@ static QString pad_number(unsigned int number, int length)
 
 QString format_time_minutes(const Timestamp& t, signed precision, bool sign)
 {
-	const Timestamp whole_seconds = floor(abs(t));
-	const Timestamp days = floor(whole_seconds / (60 * 60 * 24));
-	const unsigned int hours = fmod(whole_seconds / (60 * 60), 24).convert_to<uint>();
-	const unsigned int minutes = fmod(whole_seconds / 60, 60).convert_to<uint>();
-	const unsigned int seconds = fmod(whole_seconds, 60).convert_to<uint>();
+	// Add the maximum representation error left by the last displayed digit
+	// so we can call floor for all computed values so that we never get 24 hours or 60 seconds
+	// but still avoiding adding half precision error :
+	// 0.9 for last digit will still be represented as 1 because 0.5 have been added before calling floor
+	const Timestamp abs_t_and_floor_margin = abs(t) + ldexp(Timestamp(0.1), std::max(0, precision)) * 0.5;
+	// Do integer computation it will be faster. Also limit number of divisions (and modulos). 
+	// Note: unsigned longs (with at least 32 bits) can store at least 136 years of seconds. Should be enough...
+	const unsigned long whole_seconds = floor(abs_t_and_floor_margin).convert_to<unsigned long>();
+	const unsigned long days = std::floor(whole_seconds / (60 * 60 * 24));
+	unsigned long remain_seconds = whole_seconds - days * (60 * 60 * 24);
+	// int (with at least 16 bits) are still sufficient for remaining parts
+	const unsigned int hours = (unsigned int)std::floor(remain_seconds / (60 * 60));
+	remain_seconds -= hours * (60 * 60);
+	const unsigned int minutes = (unsigned int)std::floor(remain_seconds / 60);
+	const unsigned int seconds = (unsigned int)(remain_seconds - minutes * 60);
 
 	QString s;
 	QTextStream ts(&s);
@@ -217,7 +227,8 @@ QString format_time_minutes(const Timestamp& t, signed precision, bool sign)
 
 	// DD
 	if (days) {
-		ts << days.str().c_str() << ":";
+		ts << days << ":";
+		ts << pad_number(hours, use_padding ? 2 : 0) << ":";
 		use_padding = true;
 	}
 
@@ -238,7 +249,7 @@ QString format_time_minutes(const Timestamp& t, signed precision, bool sign)
 	if (precision) {
 		ts << ".";
 
-		const Timestamp fraction = fabs(t) - whole_seconds;
+		const Timestamp fraction = abs(t) - floor(abs(t));
 
 		ostringstream ss;
 		ss << fixed << setprecision(precision) << setfill('0') << fraction;