refactor: avoid double hashing in SourceLocationHasher #32939

1. 
   l0rinc commented at 12:46 pm on July 10, 2025: contributor

   Feeds the file name string directly into the hasher instead of pre-hashing it first. The resulting hash changes of course, but that doesn’t affect us since it’s only stored in-memory.

   Fixes: #32604 (review)

   A few other related nits were also addressed here:

   • Comment was redundant, CSipHasher is used in other hashers all over the codebase
   • static_cast<size_t> skewed the whole method, changed to shorter functional-style cast
   • struct formatting is aligned with class formatting - see https://github.com/bitcoin/bitcoin/pull/32813
2. DrahtBot added the label Refactoring on Jul 10, 2025
3. 
   DrahtBot commented at 12:47 pm on July 10, 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/32939.

   Reviews

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

4. refactor: avoid double hashing in `SourceLocationHasher`

   Feeds the file name string directly into the hasher instead of pre-hashing it first. The resulting hash changes of course, but that doesn't affect us since it's only stored in-memory.
   
   Fixes: https://github.com/bitcoin/bitcoin/pull/32604#discussion_r2188644325
   
   A few other related nits were also addressed here:
   * Comment was redundant, `CSipHasher` is used in other hashers all over the codebase
   * `static_cast<size_t>` skewed the whole method, changed to shorter functional-style cast
   * struct formatting is aligned with class formatting - see https://github.com/bitcoin/bitcoin/pull/32813

   8a618fba55
5. l0rinc force-pushed on Jul 10, 2025
6. in src/logging.h:48 in 8a618fba55

   41@@ -42,14 +42,14 @@ struct SourceLocationEqual {
   42     }
   43 };
   44 
   45-struct SourceLocationHasher {
   46+struct SourceLocationHasher
   47+{
   48     size_t operator()(const std::source_location& s) const noexcept
   49     {
   50-        // Use CSipHasher(0, 0) as a simple way to get uniform distribution.
   

   ---

   ---

   

   stickies-v commented at 1:10 pm on July 10, 2025:

   As we’ve already discussed here, I don’t think it would be an improvement to remove this comment. Using CSipHasher over std::hash is non-trivial and this comment helped me understand the code.
7. 
   stickies-v commented at 1:11 pm on July 10, 2025: contributor

   Since there are quite a few follow-ups in #32604, it might make sense to do them all in one (or at least larger, related PRs) instead of carving it out into dozens of small ones?
8. l0rinc closed this on Jul 10, 2025

   ---

Contributors
l0rinc DrahtBot stickies-v

Labels
Refactoring