Implement ECMP for unsafe_routes (#1332)

routing/gateway.go

@@ -0,0 +1,70 @@
+package routing
+
+import (
+	"fmt"
+	"net/netip"
+)
+
+const (
+	// Sentinal value
+	BucketNotCalculated = -1
+)
+
+type Gateways []Gateway
+
+func (g Gateways) String() string {
+	str := ""
+	for i, gw := range g {
+		str += gw.String()
+		if i < len(g)-1 {
+			str += ", "
+		}
+	}
+	return str
+}
+
+type Gateway struct {
+	addr             netip.Addr
+	weight           int
+	bucketUpperBound int
+}
+
+func NewGateway(addr netip.Addr, weight int) Gateway {
+	return Gateway{addr: addr, weight: weight, bucketUpperBound: BucketNotCalculated}
+}
+
+func (g *Gateway) BucketUpperBound() int {
+	return g.bucketUpperBound
+}
+
+func (g *Gateway) Addr() netip.Addr {
+	return g.addr
+}
+
+func (g *Gateway) String() string {
+	return fmt.Sprintf("{addr: %s, weight: %d}", g.addr, g.weight)
+}
+
+// Divide and round to nearest integer
+func divideAndRound(v uint64, d uint64) uint64 {
+	var tmp uint64 = v + d/2
+	return tmp / d
+}
+
+// Implements Hash-Threshold mapping, equivalent to the implementation in the linux kernel.
+// After this function returns each gateway will have a
+// positive bucketUpperBound with a maximum value of 2147483647 (INT_MAX)
+func CalculateBucketsForGateways(gateways []Gateway) {
+
+	var totalWeight int = 0
+	for i := range gateways {
+		totalWeight += gateways[i].weight
+	}
+
+	var loopWeight int = 0
+	for i := range gateways {
+		loopWeight += gateways[i].weight
+		gateways[i].bucketUpperBound = int(divideAndRound(uint64(loopWeight)<<31, uint64(totalWeight))) - 1
+	}
+
+}