introduce "type-safe" multiplication (*, uint64_t, double) -> uint64_t

stats.c

@@ -40,22 +40,24 @@ uint64_t calc_var(const uint64_t* data, size_t size, uint64_t mean) {
 	return sum / size;
 }
 
+static uint64_t mul_u64_dbl(uint64_t ul, double dbl) { return (uint64_t)((double)ul * dbl); }
+
 // Using nearest rank
 // https://en.wikipedia.org/wiki/Percentile#The_nearest-rank_method
-uint64_t get_percentile(const uint64_t* data, size_t size, float prctl) {
+uint64_t get_percentile(const uint64_t* data, size_t size, double prctl) {
 	check_saple_size(size);
 
 	if (prctl < 0 || prctl > 1) errx(EXIT_FAILURE, "prctl must be in [0,1]");
 
-	size_t n = prctl * size;
+	size_t n = mul_u64_dbl(size, prctl);
 	return data[n];
 }
 
 uint64_t get_upper_whisker(const uint64_t* data, size_t size, uintptr_t iqr) {
 	check_saple_size(size);
-	const float upper_prctl = 0.75;
-	size_t n = upper_prctl * size;
-	const uint64_t threshold = data[n] + (1.5 * iqr);
+	const double upper_prctl = 0.75;
+	size_t n = mul_u64_dbl(size, upper_prctl);
+	const uint64_t threshold = data[n] + mul_u64_dbl(iqr, 1.5);
 	while (data[n] < threshold && n < size) {
 		++n;
 	}
@@ -64,9 +66,9 @@ uint64_t get_upper_whisker(const uint64_t* data, size_t size, uintptr_t iqr) {
 
 uint64_t get_lower_whisker(const uint64_t* data, size_t size, uintptr_t iqr) {
 	check_saple_size(size);
-	const float lower_prctl = 0.25;
-	size_t n = lower_prctl * size;
-	const uint64_t threshold = data[n] - (1.5 * iqr);
+	const double lower_prctl = 0.25;
+	size_t n = mul_u64_dbl(size, lower_prctl);
+	const uint64_t threshold = data[n] - mul_u64_dbl(iqr, 1.5);
 	while (data[n] > threshold && n > 0) {
 		--n;
 	}