62 lines
2.1 KiB
C
62 lines
2.1 KiB
C
#ifndef LIGHTNING_BITCOIN_FEERATE_H
|
|
#define LIGHTNING_BITCOIN_FEERATE_H
|
|
#include "config.h"
|
|
#include <ccan/build_assert/build_assert.h>
|
|
#include <ccan/short_types/short_types.h>
|
|
#include <common/amount.h>
|
|
|
|
/* bitcoind considers 250 satoshi per kw to be the minimum acceptable fee:
|
|
* less than this won't even relay.
|
|
*/
|
|
#define BITCOIND_MINRELAYTXFEE_PER_KW 250
|
|
/*
|
|
* But bitcoind uses vbytes (ie. (weight + 3) / 4) for this
|
|
* calculation, rather than weight, meaning we can disagree since we do
|
|
* it sanely (as specified in BOLT #3).
|
|
*/
|
|
#define FEERATE_BITCOIND_SEES(feerate, weight) \
|
|
(((feerate) * (weight)) / 1000 * 1000 / ((weight) + 3))
|
|
/* ie. fee = (feerate * weight) // 1000
|
|
* bitcoind needs (worst-case): fee * 1000 / (weight + 3) >= 250
|
|
*
|
|
* (feerate * weight) // 1000 * 1000 // (weight + 3) >= 250
|
|
*
|
|
* The feerate needs to be higher for lower weight, and our minimum tx weight
|
|
* is 464 (version (4) + count_tx_in (1) + tx_in (32 + 4 + 1 + 4) +
|
|
* count_tx_out (1) + amount (8) + P2WSH (1 + 1 + 32) + witness 1 + 1 + <sig>
|
|
* + 1 + <key>). Assume it's 400 to give a significant safety margin (it
|
|
* only makes 1 difference in the result anyway).
|
|
*/
|
|
#define MINIMUM_TX_WEIGHT 400
|
|
|
|
/*
|
|
* This formula is satisfied by a feerate of 253 (hand-search).
|
|
*/
|
|
#define FEERATE_FLOOR 253
|
|
|
|
enum feerate_style {
|
|
FEERATE_PER_KSIPA,
|
|
FEERATE_PER_KBYTE
|
|
};
|
|
|
|
static inline u32 feerate_floor_check(void)
|
|
{
|
|
/* Assert that bitcoind will see this as above minRelayTxFee */
|
|
BUILD_ASSERT(FEERATE_BITCOIND_SEES(FEERATE_FLOOR, MINIMUM_TX_WEIGHT)
|
|
>= BITCOIND_MINRELAYTXFEE_PER_KW);
|
|
/* And a lesser value won't do */
|
|
BUILD_ASSERT(FEERATE_BITCOIND_SEES(FEERATE_FLOOR-1, MINIMUM_TX_WEIGHT)
|
|
< BITCOIND_MINRELAYTXFEE_PER_KW);
|
|
/* And I'm right about it being OK for larger txs, too */
|
|
BUILD_ASSERT(FEERATE_BITCOIND_SEES(FEERATE_FLOOR, (MINIMUM_TX_WEIGHT*2))
|
|
>= BITCOIND_MINRELAYTXFEE_PER_KW);
|
|
|
|
return FEERATE_FLOOR;
|
|
}
|
|
|
|
u32 feerate_from_style(u32 feerate, enum feerate_style style);
|
|
u32 feerate_to_style(u32 feerate_perkw, enum feerate_style style);
|
|
const char *feerate_style_name(enum feerate_style style);
|
|
|
|
#endif /* LIGHTNING_BITCOIN_FEERATE_H */
|