docs: add doc comment for SRD selection algorithm #33622

1. 
   yancyribbens commented at 1:05 pm on October 14, 2025: contributor

   The params documentation is missing change_fee and the description is lacking recent changes.
2. DrahtBot added the label Docs on Oct 14, 2025
3. 
   DrahtBot commented at 1:06 pm on October 14, 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/33622.

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   See the guideline for information on the review process. A summary of reviews will appear here.

4. fanquake requested review from murchandamus on Oct 14, 2025
5. 
   yancyribbens commented at 4:52 pm on October 14, 2025: contributor

   cc @furszy as related to https://github.com/bitcoin/bitcoin/issues/33168
6. in src/wallet/coinselection.cpp:538 in e6c439dcb2

   532@@ -533,6 +533,21 @@ class MinOutputGroupComparator
   533     }
   534 };
   535 
   536+/* Randomized Single Round Selection Algorithm.
   537+*
   538+* Full Description: This algorithm works by selecting inputs randomly until the target amount is
   

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   brunoerg commented at 6:46 pm on October 14, 2025:

   e6c439dcb23e1a0d03261734fd89412a15b1932a: I don’t this it needs this “Full Description:”. It seems obvious that is the description of the algorithm.

   0This algorithm works by selecting inputs randomly until the target amount is
   

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   yancyribbens commented at 8:20 pm on October 14, 2025:

   Some of the other algorithms use that wording, for example see coin-grinder: https://github.com/bitcoin/bitcoin/pull/33622/files#diff-d473ed8396f9451afb848923cfcfaa630c9811a78e07f3ae1ffd3a65da218accR208. Therefore just copying a pattern that already exists. Do you not like that wording in coin-grinder also?

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   brunoerg commented at 8:42 pm on October 14, 2025:

   I think coin grinder explanation is more complex, so that makes sense. But anyway, feel free to ignore it.

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   yancyribbens commented at 11:25 pm on October 14, 2025:

   No worries I can remove it then.
7. in src/wallet/coinselection.cpp:544 in e6c439dcb2

   539+* reached or exceeded.  If the maximum weight is exceeded, then the least valuable inputs are
   540+* removed from the selection.  In so doing, minimize the number of UTXOs included in the result
   541+* by preferring UTXOs with higher value.  Note that this selection algorithm should always produce
   542+* a non-dust change output.
   543+*
   544+* @param std::vector<OutputGroup>& utxo_pool The UTXOs that we are choosing from.
   

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   brunoerg commented at 7:04 pm on October 14, 2025:

   Aren’t there already documentation about the parameters in coinselection.h? If so, we should just add the description there instead.

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   yancyribbens commented at 8:25 pm on October 14, 2025:

   There’s not much presidence for this when looking at how the other algorithms are documented. coin-grinder seems to have it documented in both the headers file and the cpp file.

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   yancyribbens commented at 8:26 pm on October 14, 2025:

   I don’t care much either way where the doc comments are, just that it exists someplace that is findable.

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   brunoerg commented at 8:43 pm on October 14, 2025:

   I think it’s weird to have a documentation about the paratemers in coinselection.h and another documentation about the same parameters but with different wording/explanation in coinselection.cpp.

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   yancyribbens commented at 11:35 pm on October 14, 2025:

   Hmm it’s probably silly to have it both places. BnB for example does not have it’s params defined in .h at all, nor its description for that matter. And the params in .h for SRD are missing change_fee :face_palm:.

   Honestly, all these comments should be in the header file, right? It would be really hard to get people to review that kind of a change though.

8. yancyribbens force-pushed on Oct 14, 2025
9. yancyribbens force-pushed on Oct 14, 2025
10. yancyribbens force-pushed on Oct 14, 2025
11. 
    yancyribbens commented at 11:59 pm on October 14, 2025: contributor

    @brunoerg thanks for reviewing. Instead of adding new docs I improved the comments in .h instead. If only the other selection algorithms did that as well..
12. yancyribbens force-pushed on Oct 15, 2025
13. doc: add missing param description to SRD d18a88a203
14. doc: improve description for SRD selection algorithm

    Description is missing recent changes to the selection process.

    bbdfe22902
15. yancyribbens force-pushed on Oct 15, 2025

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