askrene: copy mcf.[ch] from renepay with minimal modifications.

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

plugins/askrene/mcf.h

@@ -0,0 +1,68 @@
+#ifndef LIGHTNING_PLUGINS_ASKRENE_MCF_H
+#define LIGHTNING_PLUGINS_ASKRENE_MCF_H
+/* Eduardo Quintela's (lagrang3@protonmail.com) Min Cost Flow implementation
+ * from renepay, as modified to fit askrene */
+#include "config.h"
+#include <ccan/bitmap/bitmap.h>
+#include <common/amount.h>
+#include <common/gossmap.h>
+
+struct chan_extra_map;
+
+enum {
+	RENEPAY_ERR_OK,
+	// No feasible flow found, either there is not enough known liquidity (or capacity)
+	// in the channels to complete the payment
+	RENEPAY_ERR_NOFEASIBLEFLOW,
+	// There is at least one feasible flow, but the the cheapest solution that we
+	// found is too expensive, we return the result anyways.
+	RENEPAY_ERR_NOCHEAPFLOW
+};
+
+
+
+/**
+ * optimal_payment_flow - API for min cost flow function(s).
+ * @ctx: context to allocate returned flows from
+ * @gossmap: the gossip map
+ * @source: the source to start from
+ * @target: the target to pay
+ * @chan_extra_map: hashtable of extra per-channel information
+ * @disabled: NULL, or a bitmap by channel index of channels not to use.
+ * @amount: the amount we want to reach @target
+ *
+ * @max_fee: the maximum allowed in fees
+ *
+ * @min_probability: minimum probability accepted
+ *
+ * @delay_feefactor converts 1 block delay into msat, as if it were an additional
+ * fee.  So if a CLTV delay on a node is 5 blocks, that's treated as if it
+ * were a fee of 5 * @delay_feefactor.
+ *
+ * @base_fee_penalty: factor to compute additional proportional cost from each
+ * unit of base fee. So #base_fee_penalty will be added to the effective
+ * proportional fee for each msat of base fee.
+ *
+ * 	effective_ppm = proportional_fee + base_fee_msat * base_fee_penalty
+ *
+ * @prob_cost_factor: factor used to monetize the probability cost. It is
+ * defined as the number of ppm (parts per million of the total payment) we
+ * are willing to pay to improve the probability of success by 0.1%.
+ *
+ * 	k_microsat = floor(1000*prob_cost_factor * payment_sat)
+ *
+ * this k is used to compute a prob. cost in units of microsats
+ *
+ * 	cost(payment) = - k_microsat * log Prob(payment)
+ *
+ * Return a series of subflows which deliver amount to target, or NULL.
+ */
+struct flow **minflow(const tal_t *ctx, struct gossmap *gossmap,
+		      const struct gossmap_node *source,
+		      const struct gossmap_node *target,
+		      struct chan_extra_map *chan_extra_map,
+		      const bitmap *disabled, struct amount_msat amount,
+		      struct amount_msat max_fee, double min_probability,
+		      double delay_feefactor, double base_fee_penalty,
+		      u32 prob_cost_factor, char **fail);
+#endif /* LIGHTNING_PLUGINS_ASKRENE_MCF_H */