Increase value precision in histograms from 5e-3 to 1e-12

Previously values could go into lower bucket because of too coarse precision.

Updates https://github.com/VictoriaMetrics/metrics/issues/8

histogram.go

@@ -14,7 +14,7 @@ const (
 	decimalMultiplier = 2
 	bucketSize        = 9 * decimalMultiplier
 	bucketsCount      = e10Max - e10Min
-	decimalPrecision  = 0.01 / decimalMultiplier
+	decimalPrecision  = 1e-12
 )
 
 // Histogram is a histogram for non-negative values with automatically created buckets.

histogram_test.go

@@ -55,6 +55,12 @@ func TestGetBucketIdxAndOffset(t *testing.T) {
 	f((1+prec)*math.Pow10(e10Max), -1, 2)
 	f((1+3*step+prec)*math.Pow10(e10Max), -1, 2)
 	f(math.Inf(1), -1, 2)
+
+	f(999, 11, 17)
+	f(1000, 11, 17)
+	f(1001, 12, 0)
+	f(1002, 12, 0)
+	f(1003, 12, 0)
 }
 
 func TestGetVMRange(t *testing.T) {