mempool: use FeeFrac for ancestor/descendant score comparators #32799

1. 
   theStack commented at 2:21 am on June 24, 2025: contributor

   Rather than determining fee-rates for the mempool index scores and comparators manually in a rather tedious way (even involving floating-points), use the FeeFrac class [1] to simplify and deduplicate the code. Note that though this is intended to be a refactoring PR, there might be subtle differences in behaviour due to floating-point arithmetic involved in the original code (to avoid overflows at the cost of precision loss), but these shouldn’t matter.

   [1] introduced in PR #29242, commit ce8e22542ed0b4fa5794d3203207146418d59473

2. mempool: use `FeeFrac` for calculating descendant score ac9c113bd2
3. mempool: use `FeeFrac` for calculating ancestor score 3322b3a059
4. mempool: use `FeeFrac` for calculating regular score 922adf66ac
5. DrahtBot added the label Mempool on Jun 24, 2025
6. 
   DrahtBot commented at 2:21 am on June 24, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/32799.

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   Type	Reviewers
   ACK	ismaelsadeeq, glozow

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7. ismaelsadeeq approved
8. 
   ismaelsadeeq commented at 11:16 am on June 24, 2025: member

   Code review ACK 922adf66ac7420e21ea171d3586ea84554e5d91b
9. fanquake requested review from glozow on Jun 24, 2025
10. glozow requested review from murchandamus on Jun 25, 2025
11. in src/txmempool.h:96 in 922adf66ac

    92@@ -93,36 +93,24 @@ class CompareTxMemPoolEntryByDescendantScore
    93 public:
    94     bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
    95     {
    96-        double a_mod_fee, a_size, b_mod_fee, b_size;
    97+        FeeFrac f1 = GetModFeeAndSize(a);
    

    ---

    ---

    

    glozow commented at 10:44 pm on June 26, 2025:

    nit: this (and the others) could be const
12. 
    glozow commented at 10:46 pm on June 26, 2025: member

    ACK 922adf66ac7420e21ea171d3586ea84554e5d91b great to get rid of these doubles (🤮)

Contributors
theStack DrahtBot ismaelsadeeq glozow

Review Requested
murchandamus

Labels
Mempool