routing: remove negative fee support.

We can't get them; channel_update doesn't support it.

# 1M nodes:
$ /gossipd/test/run-bench-find_route 1000000 1 > /tmp/out
=> 47677 msec

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

gossipd/routing.c

@@ -246,11 +246,11 @@ static void clear_bfg(struct node_map *nodes)
 	}
 }
 
-static s64 connection_fee(const struct node_connection *c, u64 msatoshi)
+static u64 connection_fee(const struct node_connection *c, u64 msatoshi)
 {
-	s64 fee;
+	u64 fee;
 
-	if (mul_overflows_s64(c->proportional_fee, msatoshi))
+	if (mul_overflows_u64(c->proportional_fee, msatoshi))
 		return INFINITE;
 	fee = (c->proportional_fee * msatoshi) / 1000000;
 	/* This can't overflow: c->base_fee is a u32 */
@@ -259,12 +259,8 @@ static s64 connection_fee(const struct node_connection *c, u64 msatoshi)
 
 /* Risk of passing through this channel.  We insert a tiny constant here
  * in order to prefer shorter routes, all things equal. */
-static u64 risk_fee(s64 amount, u32 delay, double riskfactor)
+static u64 risk_fee(u64 amount, u32 delay, double riskfactor)
 {
-	/* If fees are so negative we're making money, ignore risk. */
-	if (amount < 0)
-		return 1;
-
 	return 1 + amount * delay * riskfactor / BLOCKS_PER_YEAR / 10000;
 }
 
@@ -278,7 +274,7 @@ static void bfg_one_edge(struct node *node, size_t edgenum, double riskfactor)
 	assert(c->dst == node);
 	for (h = 0; h < ROUTING_MAX_HOPS; h++) {
 		/* FIXME: Bias against smaller channels. */
-		s64 fee;
+		u64 fee;
 		u64 risk;
 
 		if (node->bfg[h].total == INFINITE)
@@ -287,8 +283,8 @@ static void bfg_one_edge(struct node *node, size_t edgenum, double riskfactor)
 		fee = connection_fee(c, node->bfg[h].total);
 		risk = node->bfg[h].risk + risk_fee(node->bfg[h].total + fee,
 						    c->delay, riskfactor);
-		if (node->bfg[h].total + (s64)fee + (s64)risk
+		if (node->bfg[h].total + fee + risk
-		    < c->src->bfg[h+1].total + (s64)c->src->bfg[h+1].risk) {
+		    < c->src->bfg[h+1].total + c->src->bfg[h+1].risk) {
 			SUPERVERBOSE("...%s can reach here in hoplen %zu total %"PRIu64,
 				     type_to_string(trc, struct pubkey,
 						    &c->src->id),
@@ -303,7 +299,7 @@ static void bfg_one_edge(struct node *node, size_t edgenum, double riskfactor)
 static struct node_connection *
 find_route(const tal_t *ctx, struct routing_state *rstate,
 	   const struct pubkey *from, const struct pubkey *to, u64 msatoshi,
-	   double riskfactor, s64 *fee, struct node_connection ***route)
+	   double riskfactor, u64 *fee, struct node_connection ***route)
 {
 	struct node *n, *src, *dst;
 	struct node_map_iter it;
@@ -770,7 +766,7 @@ struct route_hop *get_route(tal_t *ctx, struct routing_state *rstate,
 	struct node_connection **route;
 	u64 total_amount;
 	unsigned int total_delay;
-	s64 fee;
+	u64 fee;
 	struct route_hop *hops;
 	int i;
 	struct node_connection *first_conn;

gossipd/routing.h

@@ -14,7 +14,7 @@ struct node_connection {
 	/* millisatoshi. */
 	u32 base_fee;
 	/* millionths */
-	s32 proportional_fee;
+	u32 proportional_fee;
 
 	/* Delay for HTLC in blocks.*/
 	u32 delay;
@@ -54,7 +54,7 @@ struct node {
 	/* Temporary data for routefinding. */
 	struct {
 		/* Total to get to here from target. */
-		s64 total;
+		u64 total;
 		/* Total risk premium of this route. */
 		u64 risk;
 		/* Where that came from. */

gossipd/test/run-bench-find_route.c

@@ -187,7 +187,7 @@ int main(int argc, char *argv[])
 	for (size_t i = 0; i < num_runs; i++) {
 		struct pubkey from = nodeid(pseudorand(num_nodes));
 		struct pubkey to = nodeid(pseudorand(num_nodes));
-		s64 fee;
+		u64 fee;
 		struct node_connection **route, *nc;
 
 		nc = find_route(ctx, rstate, &from, &to,

gossipd/test/run-find_route-specific.c

@@ -61,7 +61,7 @@ int main(void)
 	struct node_connection *nc;
 	struct routing_state *rstate;
 	struct pubkey a, b, c;
-	s64 fee;
+	u64 fee;
 	struct node_connection **route;
 
 	secp256k1_ctx = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY

gossipd/test/run-find_route.c

@@ -72,7 +72,7 @@ int main(void)
 	struct routing_state *rstate;
 	struct pubkey a, b, c, d;
 	struct privkey tmp;
-	s64 fee;
+	u64 fee;
 	struct node_connection **route;
 
 	secp256k1_ctx = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY