/// [`base_penalty_msat`]: Self::base_penalty_msat
/// [`anti_probing_penalty_msat`]: Self::anti_probing_penalty_msat
pub considered_impossible_penalty_msat: u64,
+
+ /// In order to calculate most of the scores above, we must first convert a lower and upper
+ /// bound on the available liquidity in a channel into the probability that we think a payment
+ /// will succeed. That probability is derived from a Probability Density Function for where we
+ /// think the liquidity in a channel likely lies, given such bounds.
+ ///
+ /// If this flag is set, that PDF is simply a constant - we assume that the actual available
+ /// liquidity in a channel is just as likely to be at any point between our lower and upper
+ /// bounds.
+ ///
+ /// If this flag is *not* set, that PDF is `(x - 0.5*capacity) ^ 2`. That is, we use an
+ /// exponential curve which expects the liquidity of a channel to lie "at the edges". This
+ /// matches experimental results - most routing nodes do not aggressively rebalance their
+ /// channels and flows in the network are often unbalanced, leaving liquidity usually
+ /// unavailable.
+ ///
+ /// Thus, for the "best" routes, leave this flag `false`. However, the flag does imply a number
+ /// of floating-point multiplications in the hottest routing code, which may lead to routing
+ /// performance degradation on some machines.
+ ///
+ /// Default value: false
+ pub linear_success_probability: bool,
}
impl Default for ProbabilisticScoringFeeParameters {
considered_impossible_penalty_msat: 1_0000_0000_000,
historical_liquidity_penalty_multiplier_msat: 10_000,
historical_liquidity_penalty_amount_multiplier_msat: 64,
+ linear_success_probability: false,
}
}
}
manual_node_penalties: HashMap::new(),
anti_probing_penalty_msat: 0,
considered_impossible_penalty_msat: 0,
+ linear_success_probability: true,
}
}
}
const AMOUNT_PENALTY_DIVISOR: u64 = 1 << 20;
const BASE_AMOUNT_PENALTY_DIVISOR: u64 = 1 << 30;
+/// Raises three `f64`s to the 3rd power, without `powi` because it requires `std` (dunno why).
+#[inline(always)]
+fn three_f64_pow_3(a: f64, b: f64, c: f64) -> (f64, f64, f64) {
+ (a * a * a, b * b * b, c * c * c)
+}
+
/// Given liquidity bounds, calculates the success probability (in the form of a numerator and
/// denominator) of an HTLC. This is a key assumption in our scoring models.
///
#[inline(always)]
fn success_probability(
amount_msat: u64, min_liquidity_msat: u64, max_liquidity_msat: u64, capacity_msat: u64,
- _params: &ProbabilisticScoringFeeParameters, min_zero_implies_no_successes: bool,
+ params: &ProbabilisticScoringFeeParameters, min_zero_implies_no_successes: bool,
) -> (u64, u64) {
debug_assert!(min_liquidity_msat <= amount_msat);
debug_assert!(amount_msat < max_liquidity_msat);
debug_assert!(max_liquidity_msat <= capacity_msat);
- let numerator = max_liquidity_msat - amount_msat;
- let mut denominator = (max_liquidity_msat - min_liquidity_msat).saturating_add(1);
+ let (numerator, mut denominator) =
+ if params.linear_success_probability {
+ (max_liquidity_msat - amount_msat,
+ (max_liquidity_msat - min_liquidity_msat).saturating_add(1))
+ } else {
+ let capacity = capacity_msat as f64;
+ let min = (min_liquidity_msat as f64) / capacity;
+ let max = (max_liquidity_msat as f64) / capacity;
+ let amount = (amount_msat as f64) / capacity;
+
+ // Assume the channel has a probability density function of (x - 0.5)^2 for values from
+ // 0 to 1 (where 1 is the channel's full capacity). The success probability given some
+ // liquidity bounds is thus the integral under the curve from the amount to maximum
+ // estimated liquidity, divided by the same integral from the minimum to the maximum
+ // estimated liquidity bounds.
+ //
+ // Because the integral from x to y is simply (y - 0.5)^3 - (x - 0.5)^3, we can
+ // calculate the cumulative density function between the min/max bounds trivially. Note
+ // that we don't bother to normalize the CDF to total to 1, as it will come out in the
+ // division of num / den.
+ let (max_pow, amt_pow, min_pow) = three_f64_pow_3(max - 0.5, amount - 0.5, min - 0.5);
+ let num = max_pow - amt_pow;
+ let den = max_pow - min_pow;
+
+ // Because our numerator and denominator max out at 0.5^3 we need to multiply them by
+ // quite a large factor to get something useful (ideally in the 2^30 range).
+ const BILLIONISH: f64 = 1024.0 * 1024.0 * 1024.0;
+ let numerator = (num * BILLIONISH) as u64 + 1;
+ let denominator = (den * BILLIONISH) as u64 + 1;
+ debug_assert!(numerator <= 1 << 30, "Got large numerator ({}) from float {}.", numerator, num);
+ debug_assert!(denominator <= 1 << 30, "Got large denominator ({}) from float {}.", denominator, den);
+ (numerator, denominator)
+ };
+
if min_zero_implies_no_successes && min_liquidity_msat == 0 &&
denominator < u64::max_value() / 21
{
inflight_htlc_msat: 0,
effective_capacity: EffectiveCapacity::Total { capacity_msat: 950_000_000, htlc_maximum_msat: 1_000 },
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 6262);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 11497);
let usage = ChannelUsage {
effective_capacity: EffectiveCapacity::Total { capacity_msat: 1_950_000_000, htlc_maximum_msat: 1_000 }, ..usage
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 4634);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 7408);
let usage = ChannelUsage {
effective_capacity: EffectiveCapacity::Total { capacity_msat: 2_950_000_000, htlc_maximum_msat: 1_000 }, ..usage
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 4186);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 6151);
let usage = ChannelUsage {
effective_capacity: EffectiveCapacity::Total { capacity_msat: 3_950_000_000, htlc_maximum_msat: 1_000 }, ..usage
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 3909);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 5427);
let usage = ChannelUsage {
effective_capacity: EffectiveCapacity::Total { capacity_msat: 4_950_000_000, htlc_maximum_msat: 1_000 }, ..usage
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 3556);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 4955);
let usage = ChannelUsage {
effective_capacity: EffectiveCapacity::Total { capacity_msat: 5_950_000_000, htlc_maximum_msat: 1_000 }, ..usage
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 3533);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 4736);
let usage = ChannelUsage {
effective_capacity: EffectiveCapacity::Total { capacity_msat: 6_950_000_000, htlc_maximum_msat: 1_000 }, ..usage
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 3172);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 4484);
let usage = ChannelUsage {
effective_capacity: EffectiveCapacity::Total { capacity_msat: 7_450_000_000, htlc_maximum_msat: 1_000 }, ..usage
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 3211);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 4484);
let usage = ChannelUsage {
effective_capacity: EffectiveCapacity::Total { capacity_msat: 7_950_000_000, htlc_maximum_msat: 1_000 }, ..usage
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 3243);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 4263);
let usage = ChannelUsage {
effective_capacity: EffectiveCapacity::Total { capacity_msat: 8_950_000_000, htlc_maximum_msat: 1_000 }, ..usage
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 3297);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 4263);
let usage = ChannelUsage {
effective_capacity: EffectiveCapacity::Total { capacity_msat: 9_950_000_000, htlc_maximum_msat: 1_000 }, ..usage
};
- assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 3250);
+ assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 4044);
}
#[test]
projects / rust-lightning / blobdiff