Add Round4BitMEX method

math2/math.go

@@ -29,6 +29,29 @@ func RoundToEven(x float64) float64 {
 	return t
 }
 
+// Round4BitMEX 类似四舍五入法
+// XBT: precision=0 0,0.5,1.0,1.5...
+// ETH: precision=1 0.05,0.10,0.15...
+func Round4BitMEX(x float64, precision int) float64 {
+	if precision == 0 {
+		return round4BitMEX(x)
+	}
+	p := math.Pow(10, float64(precision))
+	y := float64(round4BitMEX(x*p)) / p
+	return y
+}
+
+func round4BitMEX(x float64) float64 {
+	t := math.Trunc(x)
+	if x > t+0.5 {
+		t += 0.5
+	}
+	if d := math.Abs(x - t); d > 0.25 {
+		return t + math.Copysign(0.5, x)
+	}
+	return t
+}
+
 // RoundToEven5 类似四舍五入法，规整到 0,0.5,1.0,1.5...
 func RoundToEven5(x float64) float64 {
 	t := math.Trunc(x)