Merge rust-bitcoin/rust-bitcoin#1735: Add kilo weight unit conversion

dbd2ea07b5 Add kilo weight unit conversion (yancy)

Pull request description:

  The FeeRate module defaults to sats per `kwu` so when doing fee calculations, it would be convenient to easily convert weight to the same units.

ACKs for top commit:
  Kixunil:
    ACK dbd2ea07b5
  tcharding:
    ACK dbd2ea07b5
  apoelstra:
    ACK dbd2ea07b5

Tree-SHA512: fe26b631cf474f1dca627a4d21e9052c80f8ada9a0eb635c46b7f8f42095671b9b161fb5012b723699008372faf7668507d5e92bde7d1808d389f85dba33529b

bitcoin/src/blockdata/weight.rs

@@ -32,6 +32,9 @@ impl Weight {
     /// Directly constructs `Weight` from weight units.
     pub const fn from_wu(wu: u64) -> Self { Weight(wu) }
 
+    /// Constructs `Weight` from kilo weight units returning `None` if overflow occurred.
+    pub fn from_kwu(wu: u64) -> Option<Self> { wu.checked_mul(1000).map(Weight) }
+
     /// Constructs `Weight` from virtual bytes.
     ///
     /// # Errors
@@ -55,6 +58,9 @@ impl Weight {
     /// Can be used instead of `into()` to avoid inference issues.
     pub const fn to_wu(self) -> u64 { self.0 }
 
+    /// Converts to kilo weight units rounding down.
+    pub const fn to_kwu_floor(self) -> u64 { self.0 / 1000 }
+
     /// Converts to vB rounding down.
     pub const fn to_vbytes_floor(self) -> u64 { self.0 / 4 }
 
@@ -102,6 +108,17 @@ mod tests {
         assert_eq!(Weight::ZERO, Weight::from_wu(0));
     }
 
+    #[test]
+    fn kilo_weight_constructor_test() {
+        assert_eq!(Weight(1_000), Weight::from_kwu(1).expect("expected weight unit"));
+    }
+
+    #[test]
+    #[should_panic]
+    fn kilo_weight_constructor_panic_test() {
+        Weight::from_kwu(u64::max_value()).expect("expected weight unit");
+    }
+
     #[test]
     fn from_vb_test() {
         let vb = Weight::from_vb(1).expect("expected weight unit");
@@ -132,6 +149,11 @@ mod tests {
         assert_eq!(Weight(4), Weight::from_non_witness_data_size(1));
     }
 
+    #[test]
+    fn to_kwu_floor_test() {
+        assert_eq!(1, Weight(1_000).to_kwu_floor());
+    }
+
     #[test]
     fn to_vb_floor_test() {
         assert_eq!(1, Weight(4).to_vbytes_floor());