Fix make_fee_histogram()

Based on romanz/electrs@c88a0dc

Plus some minor refactoring

src/util/mod.rs

@@ -21,41 +21,41 @@ lazy_static! {
 
 const VSIZE_BIN_WIDTH: u32 = 50_000; // vbytes
 
-// Make the fee histogram our of a list of `getrawmempool true` entries
+// Make the fee histogram out of a list of `getrawmempool true` entries
 pub fn make_fee_histogram(mempool_entries: HashMap<Txid, Value>) -> Vec<(f32, u32)> {
-    let mut entries: Vec<(u32, f32)> = mempool_entries
-        .values()
-        .map(|entry| {
-            let size = entry["vsize"]
+    let mut entries: Vec<_> = mempool_entries
+        .into_iter()
+        .map(|(_, entry)| {
+            let vsize = entry["vsize"]
                 .as_u64()
                 .or_else(|| entry["size"].as_u64())
                 .unwrap(); // bitcoind is borked if this fails
             let fee = entry["fee"].as_f64().unwrap();
-            let feerate = fee as f32 / size as f32 * 100_000_000f32;
-            (size as u32, feerate)
+            let feerate = fee as f32 / vsize as f32 * 100_000_000f32;
+            (vsize as u32, feerate)
         })
         .collect();
 
-    // XXX we should take unconfirmed parents feerates into account
+    // XXX should take unconfirmed parents feerates into account
 
     entries.sort_unstable_by(|a, b| a.1.partial_cmp(&b.1).unwrap());
 
     let mut histogram = vec![];
     let mut bin_size = 0;
-    let mut last_feerate = None;
+    let mut last_feerate = 0.0;
 
-    for (size, feerate) in entries.into_iter().rev() {
-        bin_size += size;
-        if bin_size > VSIZE_BIN_WIDTH && last_feerate.map_or(true, |last| feerate > last) {
-            // vsize of transactions paying >= e.fee_per_vbyte()
-            histogram.push((feerate, bin_size));
+    for (vsize, feerate) in entries.into_iter().rev() {
+        if bin_size > VSIZE_BIN_WIDTH && last_feerate != feerate {
+            // vsize of transactions paying >= last_feerate
+            histogram.push((last_feerate, bin_size));
             bin_size = 0;
         }
-        last_feerate = Some(feerate);
+        bin_size += vsize;
+        last_feerate = feerate;
     }
 
-    if let Some(feerate) = last_feerate {
-        histogram.push((feerate, bin_size));
+    if bin_size > 0 {
+       histogram.push((last_feerate, bin_size));
     }
 
     histogram