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askrene: use flows array directly in remove_excess.

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We don't need the indexes array, we can use this directly.

We still set up the indexes array (for now) after we call this.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
2025-11-13 15:43:31 +10:30
parent 31d28bad86
commit 565a92e8fa
1 changed files with 43 additions and 25 deletions
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68
plugins/askrene/refine.c
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@@ -177,6 +177,15 @@ static int revcmp_flows(const size_t *a, const size_t *b, struct flow **flows)
return 1;
}
static int revcmp_flows_noidx(struct flow *const *a, struct flow *const *b, void *unused)
{
if (amount_msat_eq((*a)->delivers, (*b)->delivers))
return 0;
if (amount_msat_greater((*a)->delivers, (*b)->delivers))
return -1;
return 1;
}
// TODO: unit test:
// -> make a path
// -> compute x = flow_max_deliverable
@@ -320,36 +329,46 @@ static struct amount_msat sum_all_deliver(struct flow **flows,
return all_deliver;
}
static struct amount_msat sum_all_deliver_noidx(struct flow **flows)
{
struct amount_msat all_deliver = AMOUNT_MSAT(0);
for (size_t i = 0; i < tal_count(flows); i++) {
if (!amount_msat_accumulate(&all_deliver,
flows[i]->delivers))
abort();
}
return all_deliver;
}
/* It reduces the amount of the flows and/or removes some flows in order to
* deliver no more than max_deliver. It will leave at least one flow.
* Returns the total delivery amount. */
static struct amount_msat remove_excess(struct flow **flows,
size_t **flows_index,
static struct amount_msat remove_excess(struct flow ***flows,
struct amount_msat max_deliver)
{
if (tal_count(flows) == 0)
if (tal_count(*flows) == 0)
return AMOUNT_MSAT(0);
struct amount_msat all_deliver, excess;
all_deliver = sum_all_deliver(flows, *flows_index);
all_deliver = sum_all_deliver_noidx(*flows);
/* early exit: there is no excess */
if (!amount_msat_sub(&excess, all_deliver, max_deliver) ||
amount_msat_is_zero(excess))
return all_deliver;
asort(*flows_index, tal_count(*flows_index), revcmp_flows, flows);
asort(*flows, tal_count(*flows), revcmp_flows_noidx, NULL);
/* Remove the smaller parts if they deliver less than the
* excess. */
for (int i = tal_count(*flows_index) - 1; i >= 0; i--) {
for (int i = tal_count(*flows) - 1; i >= 0; i--) {
if (!amount_msat_deduct(&excess,
flows[(*flows_index)[i]]->delivers))
(*flows)[i]->delivers))
break;
if (!amount_msat_deduct(&all_deliver,
flows[(*flows_index)[i]]->delivers))
(*flows)[i]->delivers))
abort();
tal_arr_remove(flows_index, i);
tal_arr_remove(flows, i);
}
/* If we still have some excess, remove it from the
@@ -357,9 +376,9 @@ static struct amount_msat remove_excess(struct flow **flows,
* total. */
struct amount_msat old_excess = excess;
struct amount_msat old_deliver = all_deliver;
for (size_t i = 0; i < tal_count(*flows_index); i++) {
for (size_t i = 0; i < tal_count(*flows); i++) {
double fraction = amount_msat_ratio(
flows[(*flows_index)[i]]->delivers, old_deliver);
(*flows)[i]->delivers, old_deliver);
struct amount_msat remove;
if (!amount_msat_scale(&remove, old_excess, fraction))
@@ -372,15 +391,14 @@ static struct amount_msat remove_excess(struct flow **flows,
abort();
if (!amount_msat_deduct(&all_deliver, remove) ||
!amount_msat_deduct(&flows[(*flows_index)[i]]->delivers,
remove))
!amount_msat_deduct(&(*flows)[i]->delivers, remove))
abort();
}
/* any rounding error left, take it from the first */
assert(tal_count(*flows_index) > 0);
assert(tal_count(*flows) > 0);
if (!amount_msat_deduct(&all_deliver, excess) ||
!amount_msat_deduct(&flows[(*flows_index)[0]]->delivers, excess))
!amount_msat_deduct(&(*flows)[0]->delivers, excess))
abort();
return all_deliver;
}
@@ -464,6 +482,16 @@ const char *refine_flows(const tal_t *ctx, struct route_query *rq,
struct amount_msat *min_deliverable;
size_t *flows_index;
/* do not deliver more than HTLC_MAX allow us */
for (size_t i = 0; i < tal_count(*flows); i++) {
(*flows)[i]->delivers =
amount_msat_min((*flows)[i]->delivers,
flow_max_deliverable(rq, (*flows)[i], bottleneck_idx));
}
/* remove excess from MCF granularity if any */
remove_excess(flows, deliver);
min_deliverable = tal_arrz(working_ctx, struct amount_msat,
tal_count(*flows));
flows_index = tal_arrz(working_ctx, size_t, tal_count(*flows));
@@ -477,16 +505,6 @@ const char *refine_flows(const tal_t *ctx, struct route_query *rq,
flows_index[i] = i;
}
/* do not deliver more than HTLC_MAX allow us */
for (size_t i = 0; i < tal_count(flows_index); i++) {
(*flows)[flows_index[i]]->delivers =
amount_msat_min((*flows)[flows_index[i]]->delivers,
flow_max_deliverable(rq, (*flows)[flows_index[i]], bottleneck_idx));
}
/* remove excess from MCF granularity if any */
remove_excess(*flows, &flows_index, deliver);
/* increase flows if necessary to meet the target */
increase_flows(rq, *flows, &flows_index, deliver, /* tolerance = */ 0.02);