Change the internal representation of FeeRate

To get more precision use sats per million virtual bytes.

To make review easier keep most calls in tests using
`FeeRate::from_sats_per_kwu` and just unwrap. These can likely be
cleaned up later on if we want to.

For `serde` just change the module to `_floor` and leave it at that. The
serde stuff likely needs re-visiting before release anyways.

bitcoin/src/blockdata/script/borrowed.rs

@@ -290,7 +290,7 @@ crate::internal_macros::define_extension_trait! {
         ///
         /// [`minimal_non_dust`]: Script::minimal_non_dust
         fn minimal_non_dust_custom(&self, dust_relay: FeeRate) -> Option<Amount> {
-            self.minimal_non_dust_internal(dust_relay.to_sat_per_kvb())
+            self.minimal_non_dust_internal(dust_relay.to_sat_per_kvb_ceil())
         }
 
         /// Counts the sigops for this Script using accurate counting.

bitcoin/src/blockdata/transaction.rs

@@ -1687,7 +1687,7 @@ mod tests {
     #[test]
     fn effective_value_happy_path() {
         let value = "1 cBTC".parse::<Amount>().unwrap();
-        let fee_rate = FeeRate::from_sat_per_kwu(10);
+        let fee_rate = FeeRate::from_sat_per_kwu(10).unwrap();
         let effective_value = effective_value(fee_rate, InputWeightPrediction::P2WPKH_MAX, value);
 
         // 10 sat/kwu * 272 wu = 4 sats (rounding up)

bitcoin/src/psbt/mod.rs

@@ -1356,9 +1356,15 @@ mod tests {
     use crate::Sequence;
 
     /// Fee rate in sat/kwu for a high-fee PSBT with an input=5_000_000_000_000, output=1000
-    const ABSURD_FEE_RATE: FeeRate = FeeRate::from_sat_per_kwu(15_060_240_960_843);
+    const ABSURD_FEE_RATE: FeeRate = match FeeRate::from_sat_per_kwu(15_060_240_960_843) {
-    /// Fee rate which is just below absurd threshold (1 sat/kwu less)
+        Some(fee_rate) => fee_rate,
-    const JUST_BELOW_ABSURD_FEE_RATE: FeeRate = FeeRate::from_sat_per_kwu(15_060_240_960_842);
+        None => panic!("unreachable - no unwrap in Rust 1.63 in const"),
+    };
+    const JUST_BELOW_ABSURD_FEE_RATE: FeeRate = match FeeRate::from_sat_per_kwu(15_060_240_960_842)
+    {
+        Some(fee_rate) => fee_rate,
+        None => panic!("unreachable - no unwrap in Rust 1.63 in const"),
+    };
 
     #[track_caller]
     pub fn hex_psbt(s: &str) -> Result<Psbt, crate::psbt::error::Error> {
@@ -1475,7 +1481,7 @@ mod tests {
                 ExtractTxError::AbsurdFeeRate { fee_rate, .. } => fee_rate,
                 _ => panic!(""),
             }),
-            Err(FeeRate::from_sat_per_kwu(6250003)) // 6250000 is 25k sat/vbyte
+            Err(FeeRate::from_sat_per_kwu(6250003).unwrap()) // 6250000 is 25k sat/vbyte
         );
 
         // Lowering the input satoshis by 1 lowers the sat/kwu by 3

fuzz/fuzz_targets/bitcoin/deserialize_script.rs

@@ -17,7 +17,7 @@ fn do_test(data: &[u8]) {
         let _ = script.count_sigops_legacy();
         let _ = script.minimal_non_dust();
 
-        let fee_rate = FeeRate::from_sat_per_kwu(consume_u64(&mut new_data));
+        let fee_rate = FeeRate::from_sat_per_kwu(consume_u64(&mut new_data)).unwrap();
         let _ = script.minimal_non_dust_custom(fee_rate);
 
         let mut b = script::Builder::new();

units/src/amount/tests.rs

@@ -270,13 +270,13 @@ fn amount_checked_div_by_weight_ceil() {
     let weight = Weight::from_kwu(1).unwrap();
     let fee_rate = sat(1).checked_div_by_weight_ceil(weight).unwrap();
     // 1 sats / 1,000 wu = 1 sats/kwu
-    assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(1));
+    assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(1).unwrap());
 
     let weight = Weight::from_wu(381);
     let fee_rate = sat(329).checked_div_by_weight_ceil(weight).unwrap();
     // 329 sats / 381 wu = 863.5 sats/kwu
     // round up to 864
-    assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(864));
+    assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(864).unwrap());
 
     let fee_rate = Amount::ONE_SAT.checked_div_by_weight_ceil(Weight::ZERO);
     assert!(fee_rate.is_none());
@@ -288,13 +288,13 @@ fn amount_checked_div_by_weight_floor() {
     let weight = Weight::from_kwu(1).unwrap();
     let fee_rate = sat(1).checked_div_by_weight_floor(weight).unwrap();
     // 1 sats / 1,000 wu = 1 sats/kwu
-    assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(1));
+    assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(1).unwrap());
 
     let weight = Weight::from_wu(381);
     let fee_rate = sat(329).checked_div_by_weight_floor(weight).unwrap();
     // 329 sats / 381 wu = 863.5 sats/kwu
     // round down to 863
-    assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(863));
+    assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(863).unwrap());
 
     let fee_rate = Amount::ONE_SAT.checked_div_by_weight_floor(Weight::ZERO);
     assert!(fee_rate.is_none());
@@ -304,7 +304,7 @@ fn amount_checked_div_by_weight_floor() {
 #[test]
 fn amount_checked_div_by_fee_rate() {
     let amount = sat(1000);
-    let fee_rate = FeeRate::from_sat_per_kwu(2);
+    let fee_rate = FeeRate::from_sat_per_kwu(2).unwrap();
 
     // Test floor division
     let weight = amount.checked_div_by_fee_rate_floor(fee_rate).unwrap();
@@ -317,20 +317,20 @@ fn amount_checked_div_by_fee_rate() {
 
     // Test truncation behavior
     let amount = sat(1000);
-    let fee_rate = FeeRate::from_sat_per_kwu(3);
+    let fee_rate = FeeRate::from_sat_per_kwu(3).unwrap();
     let floor_weight = amount.checked_div_by_fee_rate_floor(fee_rate).unwrap();
     let ceil_weight = amount.checked_div_by_fee_rate_ceil(fee_rate).unwrap();
     assert_eq!(floor_weight, Weight::from_wu(333_333));
     assert_eq!(ceil_weight, Weight::from_wu(333_334));
 
     // Test division by zero
-    let zero_fee_rate = FeeRate::from_sat_per_kwu(0);
+    let zero_fee_rate = FeeRate::from_sat_per_kwu(0).unwrap();
     assert!(amount.checked_div_by_fee_rate_floor(zero_fee_rate).is_none());
     assert!(amount.checked_div_by_fee_rate_ceil(zero_fee_rate).is_none());
 
     // Test with maximum amount
     let max_amount = Amount::MAX;
-    let small_fee_rate = FeeRate::from_sat_per_kwu(1);
+    let small_fee_rate = FeeRate::from_sat_per_kwu(1).unwrap();
     let weight = max_amount.checked_div_by_fee_rate_floor(small_fee_rate).unwrap();
     // 21_000_000_0000_0000 sats / (1 sat/kwu) = 2_100_000_000_000_000_000 wu
     assert_eq!(weight, Weight::from_wu(2_100_000_000_000_000_000));

units/src/fee.rs

@@ -26,14 +26,15 @@ impl Amount {
     /// Returns [`None`] if overflow occurred.
     #[must_use]
     pub const fn checked_div_by_weight_floor(self, weight: Weight) -> Option<FeeRate> {
-        // No `?` operator in const context.
+        let wu = weight.to_wu();
-        match self.to_sat().checked_mul(1_000) {
+        if wu == 0 {
-            Some(res) => match res.checked_div(weight.to_wu()) {
+            return None;
-                Some(fee_rate) => Some(FeeRate::from_sat_per_kwu(fee_rate)),
-                None => None,
-            },
-            None => None,
         }
+
+        let sats = self.to_sat() * 1_000; // Because we use per/kwu.
+        let fee_rate = sats / wu;
+
+        FeeRate::from_sat_per_kwu(fee_rate)
     }
 
     /// Checked weight ceiling division.
@@ -51,23 +52,20 @@ impl Amount {
     /// let amount = Amount::from_sat(10)?;
     /// let weight = Weight::from_wu(300);
     /// let fee_rate = amount.checked_div_by_weight_ceil(weight);
-    /// assert_eq!(fee_rate, Some(FeeRate::from_sat_per_kwu(34)));
+    /// assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(34));
     /// # Ok::<_, amount::OutOfRangeError>(())
     /// ```
     #[must_use]
     pub fn checked_div_by_weight_ceil(self, weight: Weight) -> Option<FeeRate> {
         let wu = weight.to_wu();
-        // No `?` operator in const context.
+        if wu == 0 {
-        if let Some(sats) = self.to_sat().checked_mul(1_000) {
+            return None;
-            if let Some(wu_minus_one) = wu.checked_sub(1) {
-                if let Some(sats_plus_wu_minus_one) = sats.checked_add(wu_minus_one) {
-                    if let Some(fee_rate) = sats_plus_wu_minus_one.checked_div(wu) {
-                        return Some(FeeRate::from_sat_per_kwu(fee_rate));
         }
-                }
+
-            }
+        let sats = self.to_sat() * 1_000; // Because we use per/kwu.
-        }
+        let fee_rate = (sats + wu - 1) / wu;
-        None
+
+        FeeRate::from_sat_per_kwu(fee_rate)
     }
 
     /// Checked fee rate floor division.
@@ -346,7 +344,7 @@ mod tests {
     #[test]
     fn fee_rate_div_by_weight() {
         let fee_rate = (Amount::from_sat_u32(329) / Weight::from_wu(381)).unwrap();
-        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(863));
+        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(863).unwrap());
     }
 
     #[test]
@@ -365,7 +363,7 @@ mod tests {
             .expect("expected Amount");
         assert_eq!(Amount::from_sat_u32(100), fee);
 
-        let fee = FeeRate::from_sat_per_kwu(10).checked_mul_by_weight(Weight::MAX);
+        let fee = FeeRate::from_sat_per_kwu(10).unwrap().checked_mul_by_weight(Weight::MAX);
         assert!(fee.is_none());
 
         let weight = Weight::from_vb(3).unwrap();
@@ -374,7 +372,7 @@ mod tests {
         assert_eq!(Amount::from_sat_u32(9), fee);
 
         let weight = Weight::from_wu(381);
-        let fee_rate = FeeRate::from_sat_per_kwu(864);
+        let fee_rate = FeeRate::from_sat_per_kwu(864).unwrap();
         let fee = weight.checked_mul_by_fee_rate(fee_rate).unwrap();
         // 381 * 0.864 yields 329.18.
         // The result is then rounded up to 330.
@@ -401,7 +399,7 @@ mod tests {
     fn amount_div_by_fee_rate() {
         // Test exact division
         let amount = Amount::from_sat_u32(1000);
-        let fee_rate = FeeRate::from_sat_per_kwu(2);
+        let fee_rate = FeeRate::from_sat_per_kwu(2).unwrap();
         let weight = (amount / fee_rate).unwrap();
         assert_eq!(weight, Weight::from_wu(500_000));
 
@@ -415,7 +413,7 @@ mod tests {
 
         // Test truncation behavior
         let amount = Amount::from_sat_u32(1000);
-        let fee_rate = FeeRate::from_sat_per_kwu(3);
+        let fee_rate = FeeRate::from_sat_per_kwu(3).unwrap();
         let weight = (amount / fee_rate).unwrap();
         // 1000 * 1000 = 1,000,000 msats
         // 1,000,000 / 3 = 333,333.33... wu
@@ -427,7 +425,7 @@ mod tests {
         assert_eq!(ceil_weight, Weight::from_wu(333_334));
 
         // Test that division by zero returns None
-        let zero_rate = FeeRate::from_sat_per_kwu(0);
+        let zero_rate = FeeRate::from_sat_per_kwu(0).unwrap();
         assert!(amount.checked_div_by_fee_rate_floor(zero_rate).is_none());
         assert!(amount.checked_div_by_fee_rate_ceil(zero_rate).is_none());
     }

units/src/fee_rate/mod.rs

@@ -22,7 +22,7 @@ impl FeeRate {
     /// 0 sat/kwu.
     ///
     /// Equivalent to [`MIN`](Self::MIN), may better express intent in some contexts.
-    pub const ZERO: FeeRate = FeeRate::from_sat_per_kwu(0);
+    pub const ZERO: FeeRate = FeeRate::from_sat_per_mvb(0);
 
     /// Minimum possible value (0 sat/kwu).
     ///
@@ -30,7 +30,7 @@ impl FeeRate {
     pub const MIN: FeeRate = FeeRate::ZERO;
 
     /// Maximum possible value.
-    pub const MAX: FeeRate = FeeRate::from_sat_per_kwu(u64::MAX / 4_000);
+    pub const MAX: FeeRate = FeeRate::from_sat_per_mvb(u64::MAX);
 
     /// Minimum fee rate required to broadcast a transaction.
     ///
@@ -40,46 +40,66 @@ impl FeeRate {
     /// Fee rate used to compute dust amount.
     pub const DUST: FeeRate = FeeRate::from_sat_per_vb_u32(3);
 
+    /// Constructs a new [`FeeRate`] from satoshis per 1,000,000 virtual bytes.
+    pub(crate) const fn from_sat_per_mvb(sat_mvb: u64) -> Self { Self(sat_mvb) }
+
     /// Constructs a new [`FeeRate`] from satoshis per 1000 weight units.
-    pub const fn from_sat_per_kwu(sat_kwu: u64) -> Self { FeeRate(sat_kwu) }
+    pub const fn from_sat_per_kwu(sat_kwu: u64) -> Option<Self> {
+        // No `map()` in const context.
+        match sat_kwu.checked_mul(4_000) {
+            Some(fee_rate) => Some(FeeRate::from_sat_per_mvb(fee_rate)),
+            None => None,
+        }
+    }
 
     /// Constructs a new [`FeeRate`] from satoshis per virtual bytes.
     ///
     /// # Errors
     ///
     /// Returns [`None`] on arithmetic overflow.
-    pub fn from_sat_per_vb(sat_vb: u64) -> Option<Self> {
+    pub const fn from_sat_per_vb(sat_vb: u64) -> Option<Self> {
-        // 1 vb == 4 wu
+        // No `map()` in const context.
-        // 1 sat/vb == 1/4 sat/wu
+        match sat_vb.checked_mul(1_000_000) {
-        // sat/vb * 1000 / 4 == sat/kwu
+            Some(fee_rate) => Some(FeeRate::from_sat_per_mvb(fee_rate)),
-        Some(FeeRate::from_sat_per_kwu(sat_vb.checked_mul(1000 / 4)?))
+            None => None,
+        }
     }
 
     /// Constructs a new [`FeeRate`] from satoshis per virtual bytes.
     pub const fn from_sat_per_vb_u32(sat_vb: u32) -> Self {
         let sat_vb = sat_vb as u64; // No `Into` in const context.
-        FeeRate::from_sat_per_kwu(sat_vb * (1000 / 4))
+        FeeRate::from_sat_per_mvb(sat_vb * 1_000_000)
     }
 
     /// Constructs a new [`FeeRate`] from satoshis per kilo virtual bytes (1,000 vbytes).
-    pub const fn from_sat_per_kvb(sat_kvb: u64) -> Self { FeeRate::from_sat_per_kwu(sat_kvb / 4) }
+    pub const fn from_sat_per_kvb(sat_kvb: u64) -> Option<Self> {
-
+        // No `map()` in const context.
-    /// Converts to sat/kwu rounding down.
+        match sat_kvb.checked_mul(1_000) {
-    pub const fn to_sat_per_kwu_floor(self) -> u64 { self.0 }
+            Some(fee_rate) => Some(FeeRate::from_sat_per_mvb(fee_rate)),
-
+            None => None,
-    /// Converts to sat/kwu rounding up.
+        }
-    pub const fn to_sat_per_kwu_ceil(self) -> u64 { self.0 }
-
-    /// Converts to sat/vB rounding down.
-    pub const fn to_sat_per_vb_floor(self) -> u64 { self.to_sat_per_kwu_floor() / (1000 / 4) }
-
-    /// Converts to sat/vB rounding up.
-    pub const fn to_sat_per_vb_ceil(self) -> u64 {
-        (self.to_sat_per_kwu_floor() + (1000 / 4 - 1)) / (1000 / 4)
     }
 
-    /// Converts to sat/kvb.
+    /// Converts to sat/MvB.
-    pub const fn to_sat_per_kvb(self) -> u64 { self.to_sat_per_kwu_floor() * 4 }
+    pub(crate) const fn to_sat_per_mvb(self) -> u64 { self.0 }
+
+    /// Converts to sat/kwu rounding down.
+    pub const fn to_sat_per_kwu_floor(self) -> u64 { self.to_sat_per_mvb() / 4_000 }
+
+    /// Converts to sat/kwu rounding up.
+    pub const fn to_sat_per_kwu_ceil(self) -> u64 { (self.to_sat_per_mvb() + 3_999) / 4_000 }
+
+    /// Converts to sat/vB rounding down.
+    pub const fn to_sat_per_vb_floor(self) -> u64 { self.to_sat_per_mvb() / 1_000_000 }
+
+    /// Converts to sat/vB rounding up.
+    pub const fn to_sat_per_vb_ceil(self) -> u64 { (self.to_sat_per_mvb() + 999_999) / 1_000_000 }
+
+    /// Converts to sat/kvb rounding down.
+    pub const fn to_sat_per_kvb_floor(self) -> u64 { self.to_sat_per_mvb() / 1_000 }
+
+    /// Converts to sat/kvb rounding up.
+    pub const fn to_sat_per_kvb_ceil(self) -> u64 { (self.to_sat_per_mvb() + 999) / 1_000 }
 
     /// Checked multiplication.
     ///
@@ -87,8 +107,8 @@ impl FeeRate {
     #[must_use]
     pub const fn checked_mul(self, rhs: u64) -> Option<Self> {
         // No `map()` in const context.
-        match self.to_sat_per_kwu_floor().checked_mul(rhs) {
+        match self.to_sat_per_mvb().checked_mul(rhs) {
-            Some(res) => Some(Self::from_sat_per_kwu(res)),
+            Some(res) => Some(Self::from_sat_per_mvb(res)),
             None => None,
         }
     }
@@ -99,8 +119,8 @@ impl FeeRate {
     #[must_use]
     pub const fn checked_div(self, rhs: u64) -> Option<Self> {
         // No `map()` in const context.
-        match self.to_sat_per_kwu_floor().checked_div(rhs) {
+        match self.to_sat_per_mvb().checked_div(rhs) {
-            Some(res) => Some(Self::from_sat_per_kwu(res)),
+            Some(res) => Some(Self::from_sat_per_mvb(res)),
             None => None,
         }
     }
@@ -111,8 +131,8 @@ impl FeeRate {
     #[must_use]
     pub const fn checked_add(self, rhs: FeeRate) -> Option<Self> {
         // No `map()` in const context.
-        match self.to_sat_per_kwu_floor().checked_add(rhs.to_sat_per_kwu_floor()) {
+        match self.to_sat_per_mvb().checked_add(rhs.to_sat_per_mvb()) {
-            Some(res) => Some(Self::from_sat_per_kwu(res)),
+            Some(res) => Some(Self::from_sat_per_mvb(res)),
             None => None,
         }
     }
@@ -123,8 +143,8 @@ impl FeeRate {
     #[must_use]
     pub const fn checked_sub(self, rhs: FeeRate) -> Option<Self> {
         // No `map()` in const context.
-        match self.to_sat_per_kwu_floor().checked_sub(rhs.to_sat_per_kwu_floor()) {
+        match self.to_sat_per_mvb().checked_sub(rhs.to_sat_per_mvb()) {
-            Some(res) => Some(Self::from_sat_per_kwu(res)),
+            Some(res) => Some(Self::from_sat_per_mvb(res)),
             None => None,
         }
     }
@@ -134,19 +154,19 @@ crate::internal_macros::impl_op_for_references! {
     impl ops::Add<FeeRate> for FeeRate {
         type Output = FeeRate;
 
-        fn add(self, rhs: FeeRate) -> Self::Output { FeeRate::from_sat_per_kwu(self.to_sat_per_kwu_floor() + rhs.to_sat_per_kwu_floor()) }
+        fn add(self, rhs: FeeRate) -> Self::Output { FeeRate::from_sat_per_mvb(self.to_sat_per_mvb() + rhs.to_sat_per_mvb()) }
     }
 
     impl ops::Sub<FeeRate> for FeeRate {
         type Output = FeeRate;
 
-        fn sub(self, rhs: FeeRate) -> Self::Output { FeeRate::from_sat_per_kwu(self.to_sat_per_kwu_floor() - rhs.to_sat_per_kwu_floor()) }
+        fn sub(self, rhs: FeeRate) -> Self::Output { FeeRate::from_sat_per_mvb(self.to_sat_per_mvb() - rhs.to_sat_per_mvb()) }
     }
 
     impl ops::Div<NonZeroU64> for FeeRate {
         type Output = FeeRate;
 
-        fn div(self, rhs: NonZeroU64) -> Self::Output{ Self::from_sat_per_kwu(self.to_sat_per_kwu_floor() / rhs.get()) }
+        fn div(self, rhs: NonZeroU64) -> Self::Output{ Self::from_sat_per_mvb(self.to_sat_per_mvb() / rhs.get()) }
     }
 }
 crate::internal_macros::impl_add_assign!(FeeRate);
@@ -157,7 +177,7 @@ impl core::iter::Sum for FeeRate {
     where
         I: Iterator<Item = Self>,
     {
-        FeeRate::from_sat_per_kwu(iter.map(FeeRate::to_sat_per_kwu_floor).sum())
+        FeeRate::from_sat_per_mvb(iter.map(FeeRate::to_sat_per_mvb).sum())
     }
 }
 
@@ -166,7 +186,7 @@ impl<'a> core::iter::Sum<&'a FeeRate> for FeeRate {
     where
         I: Iterator<Item = &'a FeeRate>,
     {
-        FeeRate::from_sat_per_kwu(iter.map(|f| FeeRate::to_sat_per_kwu_floor(*f)).sum())
+        FeeRate::from_sat_per_mvb(iter.map(|f| FeeRate::to_sat_per_mvb(*f)).sum())
     }
 }
 
@@ -179,7 +199,7 @@ impl<'a> Arbitrary<'a> for FeeRate {
             1 => Ok(FeeRate::BROADCAST_MIN),
             2 => Ok(FeeRate::DUST),
             3 => Ok(FeeRate::MAX),
-            _ => Ok(FeeRate::from_sat_per_kwu(u64::arbitrary(u)?)),
+            _ => Ok(FeeRate::from_sat_per_mvb(u64::arbitrary(u)?)),
         }
     }
 }
@@ -193,18 +213,18 @@ mod tests {
     #[test]
     #[allow(clippy::op_ref)]
     fn feerate_div_nonzero() {
-        let rate = FeeRate::from_sat_per_kwu(200);
+        let rate = FeeRate::from_sat_per_kwu(200).unwrap();
         let divisor = NonZeroU64::new(2).unwrap();
-        assert_eq!(rate / divisor, FeeRate::from_sat_per_kwu(100));
+        assert_eq!(rate / divisor, FeeRate::from_sat_per_kwu(100).unwrap());
-        assert_eq!(&rate / &divisor, FeeRate::from_sat_per_kwu(100));
+        assert_eq!(&rate / &divisor, FeeRate::from_sat_per_kwu(100).unwrap());
     }
 
     #[test]
     #[allow(clippy::op_ref)]
     fn addition() {
-        let one = FeeRate::from_sat_per_kwu(1);
+        let one = FeeRate::from_sat_per_kwu(1).unwrap();
-        let two = FeeRate::from_sat_per_kwu(2);
+        let two = FeeRate::from_sat_per_kwu(2).unwrap();
-        let three = FeeRate::from_sat_per_kwu(3);
+        let three = FeeRate::from_sat_per_kwu(3).unwrap();
 
         assert!(one + two == three);
         assert!(&one + two == three);
@@ -215,9 +235,9 @@ mod tests {
     #[test]
     #[allow(clippy::op_ref)]
     fn subtract() {
-        let three = FeeRate::from_sat_per_kwu(3);
+        let three = FeeRate::from_sat_per_kwu(3).unwrap();
-        let seven = FeeRate::from_sat_per_kwu(7);
+        let seven = FeeRate::from_sat_per_kwu(7).unwrap();
-        let ten = FeeRate::from_sat_per_kwu(10);
+        let ten = FeeRate::from_sat_per_kwu(10).unwrap();
 
         assert_eq!(ten - seven, three);
         assert_eq!(&ten - seven, three);
@@ -227,43 +247,44 @@ mod tests {
 
     #[test]
     fn add_assign() {
-        let mut f = FeeRate::from_sat_per_kwu(1);
+        let mut f = FeeRate::from_sat_per_kwu(1).unwrap();
-        f += FeeRate::from_sat_per_kwu(2);
+        f += FeeRate::from_sat_per_kwu(2).unwrap();
-        assert_eq!(f, FeeRate::from_sat_per_kwu(3));
+        assert_eq!(f, FeeRate::from_sat_per_kwu(3).unwrap());
 
-        let mut f = FeeRate::from_sat_per_kwu(1);
+        let mut f = FeeRate::from_sat_per_kwu(1).unwrap();
-        f += &FeeRate::from_sat_per_kwu(2);
+        f += &FeeRate::from_sat_per_kwu(2).unwrap();
-        assert_eq!(f, FeeRate::from_sat_per_kwu(3));
+        assert_eq!(f, FeeRate::from_sat_per_kwu(3).unwrap());
     }
 
     #[test]
     fn sub_assign() {
-        let mut f = FeeRate::from_sat_per_kwu(3);
+        let mut f = FeeRate::from_sat_per_kwu(3).unwrap();
-        f -= FeeRate::from_sat_per_kwu(2);
+        f -= FeeRate::from_sat_per_kwu(2).unwrap();
-        assert_eq!(f, FeeRate::from_sat_per_kwu(1));
+        assert_eq!(f, FeeRate::from_sat_per_kwu(1).unwrap());
 
-        let mut f = FeeRate::from_sat_per_kwu(3);
+        let mut f = FeeRate::from_sat_per_kwu(3).unwrap();
-        f -= &FeeRate::from_sat_per_kwu(2);
+        f -= &FeeRate::from_sat_per_kwu(2).unwrap();
-        assert_eq!(f, FeeRate::from_sat_per_kwu(1));
+        assert_eq!(f, FeeRate::from_sat_per_kwu(1).unwrap());
     }
 
     #[test]
     fn checked_add() {
-        let one = FeeRate::from_sat_per_kwu(1);
+        let one = FeeRate::from_sat_per_kwu(1).unwrap();
-        let two = FeeRate::from_sat_per_kwu(2);
+        let two = FeeRate::from_sat_per_kwu(2).unwrap();
-        let three = FeeRate::from_sat_per_kwu(3);
+        let three = FeeRate::from_sat_per_kwu(3).unwrap();
 
         assert_eq!(one.checked_add(two).unwrap(), three);
 
-        let fee_rate = FeeRate::from_sat_per_kwu(u64::MAX).checked_add(one);
+        assert!(FeeRate::from_sat_per_kvb(u64::MAX).is_none()); // sanity check.
+        let fee_rate = FeeRate::from_sat_per_mvb(u64::MAX).checked_add(one);
         assert!(fee_rate.is_none());
     }
 
     #[test]
     fn checked_sub() {
-        let one = FeeRate::from_sat_per_kwu(1);
+        let one = FeeRate::from_sat_per_kwu(1).unwrap();
-        let two = FeeRate::from_sat_per_kwu(2);
+        let two = FeeRate::from_sat_per_kwu(2).unwrap();
-        let three = FeeRate::from_sat_per_kwu(3);
+        let three = FeeRate::from_sat_per_kwu(3).unwrap();
         assert_eq!(three.checked_sub(two).unwrap(), one);
 
         let fee_rate = FeeRate::ZERO.checked_sub(one);
@@ -282,13 +303,13 @@ mod tests {
     #[test]
     fn fee_rate_from_sat_per_vb() {
         let fee_rate = FeeRate::from_sat_per_vb(10).expect("expected feerate in sat/kwu");
-        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(2500));
+        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(2500).unwrap());
     }
 
     #[test]
     fn fee_rate_from_sat_per_kvb() {
-        let fee_rate = FeeRate::from_sat_per_kvb(11);
+        let fee_rate = FeeRate::from_sat_per_kvb(11).unwrap();
-        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(2));
+        assert_eq!(fee_rate, FeeRate::from_sat_per_mvb(11_000));
     }
 
     #[test]
@@ -300,7 +321,7 @@ mod tests {
     #[test]
     fn from_sat_per_vb_u32() {
         let fee_rate = FeeRate::from_sat_per_vb_u32(10);
-        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(2500));
+        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(2500).unwrap());
     }
 
     #[test]
@@ -309,7 +330,7 @@ mod tests {
 
     #[test]
     fn raw_feerate() {
-        let fee_rate = FeeRate::from_sat_per_kwu(749);
+        let fee_rate = FeeRate::from_sat_per_kwu(749).unwrap();
         assert_eq!(fee_rate.to_sat_per_kwu_floor(), 749);
         assert_eq!(fee_rate.to_sat_per_vb_floor(), 2);
         assert_eq!(fee_rate.to_sat_per_vb_ceil(), 3);
@@ -317,21 +338,32 @@ mod tests {
 
     #[test]
     fn checked_mul() {
-        let fee_rate =
+        let fee_rate = FeeRate::from_sat_per_kwu(10)
-            FeeRate::from_sat_per_kwu(10).checked_mul(10).expect("expected feerate in sat/kwu");
+            .unwrap()
-        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(100));
+            .checked_mul(10)
+            .expect("expected feerate in sat/kwu");
+        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(100).unwrap());
 
-        let fee_rate = FeeRate::from_sat_per_kwu(10).checked_mul(u64::MAX);
+        let fee_rate = FeeRate::from_sat_per_kwu(10).unwrap().checked_mul(u64::MAX);
         assert!(fee_rate.is_none());
     }
 
     #[test]
     fn checked_div() {
-        let fee_rate =
+        let fee_rate = FeeRate::from_sat_per_kwu(10)
-            FeeRate::from_sat_per_kwu(10).checked_div(10).expect("expected feerate in sat/kwu");
+            .unwrap()
-        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(1));
+            .checked_div(10)
+            .expect("expected feerate in sat/kwu");
+        assert_eq!(fee_rate, FeeRate::from_sat_per_kwu(1).unwrap());
 
-        let fee_rate = FeeRate::from_sat_per_kwu(10).checked_div(0);
+        let fee_rate = FeeRate::from_sat_per_kwu(10).unwrap().checked_div(0);
         assert!(fee_rate.is_none());
     }
+
+    #[test]
+    fn mvb() {
+        let fee_rate = FeeRate::from_sat_per_mvb(1_234_567);
+        let got = fee_rate.to_sat_per_mvb();
+        assert_eq!(got, 1_234_567);
+    }
 }

units/src/fee_rate/serde.rs

@@ -18,7 +18,7 @@
 //!
 //! #[derive(Serialize, Deserialize)]
 //! pub struct Foo {
-//!     #[serde(with = "fee_rate::serde::as_sat_per_kwu")]
+//!     #[serde(with = "fee_rate::serde::as_sat_per_kwu_floor")]
 //!     pub fee_rate: FeeRate,
 //! }
 //! ```
@@ -26,7 +26,7 @@
 use core::convert::Infallible;
 use core::fmt;
 
-pub mod as_sat_per_kwu {
+pub mod as_sat_per_kwu_floor {
     //! Serialize and deserialize [`FeeRate`] denominated in satoshis per 1000 weight units.
     //!
     //! Use with `#[serde(with = "fee_rate::serde::as_sat_per_kwu")]`.
@@ -40,7 +40,8 @@ pub mod as_sat_per_kwu {
     }
 
     pub fn deserialize<'d, D: Deserializer<'d>>(d: D) -> Result<FeeRate, D::Error> {
-        Ok(FeeRate::from_sat_per_kwu(u64::deserialize(d)?))
+        FeeRate::from_sat_per_kwu(u64::deserialize(d)?)
+            .ok_or_else(|| serde::de::Error::custom("overflowed sats/kwu"))
     }
 
     pub mod opt {

units/tests/serde.rs

@@ -37,13 +37,13 @@ struct Serde {
     vb_floor: FeeRate,
     #[serde(with = "fee_rate::serde::as_sat_per_vb_ceil")]
     vb_ceil: FeeRate,
-    #[serde(with = "fee_rate::serde::as_sat_per_kwu")]
+    #[serde(with = "fee_rate::serde::as_sat_per_kwu_floor")]
     kwu: FeeRate,
     #[serde(with = "fee_rate::serde::as_sat_per_vb_floor::opt")]
     opt_vb_floor: Option<FeeRate>,
     #[serde(with = "fee_rate::serde::as_sat_per_vb_ceil::opt")]
     opt_vb_ceil: Option<FeeRate>,
-    #[serde(with = "fee_rate::serde::as_sat_per_kwu::opt")]
+    #[serde(with = "fee_rate::serde::as_sat_per_kwu_floor::opt")]
     opt_kwu: Option<FeeRate>,
 
     a: BlockHeight,