ReferenceSampleTree Random Access #983
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qec-pconner
commented
Aug 2, 2025
* Adding `operator[]` to `ReferenceSampleTree`. * Allows quick access to any reference sample bit within the tree at a given absolute index. * Updating `src/stim/util_top/reference_sample_tree.test.cc` to check bit positions, as applicable.
* Faster random access. * Iterate once for shallow access (if desired index is in first pass), also measures size. * From desired index and size, extrapolate iteration value. * Jump forward to the correct iteration value and iterate through childen (second pass). * Adding `<< "index: " << index` output for `ASSERT_EQ` in `src/stim/util_top/reference_sample_tree.test.cc` for easier test debugging.
…or[]` for a tree of >10^17 bits (encoded into 5 nodes). * Iterates over the beginning, the end, and 1 outer repetition before the end. * Test case finishes in <1ms.
* Helps detect when the size of any node is larger than `ULLONG_MAX` instead of silently overflowing.
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qec-pconner
commented
Aug 4, 2025
* Better compat for inconsistent `long` vs `long long` ABIs.
Strilanc
requested changes
Aug 5, 2025
* `unsigned long long` necessary (instead of just `uint64_t`) due to incompatible type usage between ABIs.
… support for BMI2. * Adding windows-specific overflow check, via `_umul128()`. * Adding fallback overflow check in `#else` clause.
Strilanc
approved these changes
Aug 5, 2025
* `_umul128()` not supported on 32-bit windows. * 32-bit windows will then fallback to the `#else`'s general assertion.
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operator[]toReferenceSampleTree.src/stim/util_top/reference_sample_tree.test.ccto check bit positions, as applicable.