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dijkstra: fix heap ordering.

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We were always ordering heap by distance, not score (which are different
if we are routing by cheapest, not shortest!).

This simplifies our callbacks, too.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
2020-10-20 14:28:06 +10:30
parent 4a1843a151
commit 1bf3eebbf6
6 changed files with 49 additions and 85 deletions
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42
common/dijkstra.c
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@@ -22,6 +22,9 @@ struct dijkstra {
/* NULL means it's been visited already. */
const struct gossmap_node **heapptr;
/* How we decide "best" */
u64 score;
/* We could re-evaluate to determine this, but keeps it simple */
struct gossmap_chan *best_chan;
};
@@ -67,9 +70,9 @@ static int less_comparer(const void *const ctx,
const void *const b)
{
return get_dijkstra(global_dijkstra, global_map,
*(struct gossmap_node **)a)->distance
*(struct gossmap_node **)a)->score
> get_dijkstra(global_dijkstra, global_map,
*(struct gossmap_node **)b)->distance;
*(struct gossmap_node **)b)->score;
}
static void item_mover(void *const dst, const void *const src)
@@ -101,6 +104,7 @@ static const struct gossmap_node **mkheap(const tal_t *ctx,
d->distance = 0;
d->total_delay = 0;
d->cost = sent;
d->score = 0;
i--;
} else {
heap[i] = n;
@@ -108,6 +112,7 @@ static const struct gossmap_node **mkheap(const tal_t *ctx,
d->distance = UINT_MAX;
d->cost = AMOUNT_MSAT(-1ULL);
d->total_delay = 0;
d->score = -1ULL;
}
}
assert(i == tal_count(heap));
@@ -142,13 +147,9 @@ dijkstra_(const tal_t *ctx,
int dir,
struct amount_msat amount,
void *arg),
bool (*path_better)(u32 old_distance,
u32 new_distance,
struct amount_msat old_cost,
struct amount_msat new_cost,
struct amount_msat old_risk,
struct amount_msat new_risk,
void *arg),
u64 (*path_score)(u32 distance,
struct amount_msat cost,
struct amount_msat risk),
void *arg)
{
struct dijkstra *dij;
@@ -229,7 +230,8 @@ dijkstra_(const tal_t *ctx,
int which_half;
struct gossmap_chan *c;
struct dijkstra *d;
struct amount_msat cost, new_risk, old_risk;
struct amount_msat cost, risk;
u64 score;
c = gossmap_nth_chan(map, cur, i, &which_half);
neighbor = gossmap_nth_node(map, c, !which_half);
@@ -251,20 +253,11 @@ dijkstra_(const tal_t *ctx,
continue;
/* cltv_delay can't overflow: only 20 bits per hop. */
new_risk = risk_price(cost, riskfactor,
cur_d->total_delay
+ c->half[!which_half].delay);
old_risk = risk_price(d->cost, riskfactor,
d->total_delay);
if (!path_better(d->distance,
cur_d->distance + 1,
d->cost,
cost,
old_risk,
new_risk,
arg))
risk = risk_price(cost, riskfactor,
cur_d->total_delay
+ c->half[!which_half].delay);
score = path_score(cur_d->distance + 1, cost, risk);
if (score >= d->score)
continue;
d->distance = cur_d->distance + 1;
@@ -272,6 +265,7 @@ dijkstra_(const tal_t *ctx,
+ c->half[!which_half].delay;
d->cost = cost;
d->best_chan = c;
d->score = score;
gheap_restore_heap_after_item_increase(&gheap_ctx,
heap, heapsize,
d->heapptr - heap);