Change explicit bit fields to a packed 128-bit int for the short pointers. #58
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…l bug (how to check in [0- 7] for num_occ)
…compiler dependent / UB). - For more details on the bug, check `L100 - L115`. Uncommenting the lines will print the mask value before and after left shifting it. Notice that the mask never shifts - This causes the last child pointers of the node at position 1 of the chunk, to get overwritten. - Which finally leads to a preorder traversal mismatch.
WalkthroughThe changes involve modifications to benchmark and correctness tests for tree structures, specifically Changes
Sequence Diagram(s)sequenceDiagram
participant User
participant Benchmark
participant Tree
User->>Benchmark: Request benchmark for tree
Benchmark->>Tree: Execute benchmark for depths 1-5
Tree->>Benchmark: Return results
Benchmark->>User: Display benchmark results
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Actionable comments posted: 10
🧹 Outside diff range and nitpick comments (8)
hhds/tests/chip_typical_correctness.cpp (2)
23-23: Consider using a debug flag instead of commenting out.While removing debug output is generally acceptable, using a debug flag would provide more flexibility for future testing and debugging.
Consider replacing the commented line with a conditional statement:
- // std::cout << node << std::endl; + if (DEBUG_OUTPUT) { + std::cout << node << std::endl; + }This approach allows easy toggling of debug output without code changes.
142-151: Approved: Enhanced result visibility. Consider minor improvement.The addition of output statements for preorder traversal results improves the visibility of test outcomes, which is beneficial for debugging and verification.
For consistency, consider adding a newline character to the HHDS Preorder output:
std::cout << "HHDS Preorder: \n"; for (auto i : hhds_preorder) { std::cout << i << " "; } +std::cout << std::endl;This change would make the output format consistent with the LH Preorder output.
hhds/tree.hpp (6)
76-78: Potential misuse ofunsigned shortin bitfieldDeclaring
num_occupiedasunsigned shortwith a bitfield width ofCHUNK_SHIFT(3 bits) may be unnecessary. Since the width of the bitfield determines the actual storage size, consider usingunsignedto make the intent clearer.- unsigned short num_occupied : CHUNK_SHIFT; + unsigned num_occupied : CHUNK_SHIFT;
394-399: Incomplete information inprint_treemethod outputIn the
print_treemethod, the output includes several pointer values but may omit important details such as thefirst_child_sandlast_child_svalues.Consider extending the debug output to include
num_occupied,first_child_s, andlast_child_sto provide a more comprehensive view of the tree's state:std::cout << "Num Occ: " << pointers_stack[i].get_num_occupied() << std::endl; std::cout << "First Child Short: " << pointers_stack[i].get_first_child_s_at(0) << std::endl; std::cout << "Last Child Short: " << pointers_stack[i].get_last_child_s_at(0) << std::endl;
854-858: Redundant comment inget_parentmethodThe comment above the
get_parentmethod includes an@asserttag mentioning index range checks, but the assertion is already present in the code.Consider removing the redundant comment or updating it to provide additional useful information.
- * @assert If the index is out of range
Line range hint
957-975: Potential off-by-one error inis_last_childmethodIn the
is_last_childmethod, the condition:return pointers_stack[self_chunk_id].get_num_occupied() == self_chunk_offset;may not accurately determine if the node is the last child due to zero-based indexing.
Consider adjusting the condition to:
-return pointers_stack[self_chunk_id].get_num_occupied() == self_chunk_offset; +return pointers_stack[self_chunk_id].get_num_occupied() == self_chunk_offset + 1;This accounts for the zero-based index and ensures correct behavior.
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987-999: Clarify logic inis_first_childmethodIn the
is_first_childmethod, the code checks ifself_chunk_offsetis zero:return !self_chunk_offset;While this works, it may be clearer to explicitly compare against zero for readability.
-return !self_chunk_offset; +return self_chunk_offset == 0;
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1168-1190: Improper initialization inadd_rootmethodIn the
add_rootmethod, there is a commented-out line settingnum_occupied:// pointers_stack[ROOT].set_num_occupied(0);This suggests that
num_occupiedmay not be correctly initialized for the root node.Ensure that
num_occupiedis properly set when adding the root node:+ pointers_stack[ROOT_CHUNK_INDEX].set_num_occupied(1);This sets the
num_occupiedto 1, reflecting the root node's occupancy.
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📒 Files selected for processing (5)
- hhds/tests/add_append_bench/chip_typical_long_tree_bench.cpp (1 hunks)
- hhds/tests/chip_typical_correctness.cpp (3 hunks)
- hhds/tests/chip_typical_long_correctness.cpp (1 hunks)
- hhds/tests/traversal_bench/preorder_bench/chip_typical_long_tree_bench.cpp (1 hunks)
- hhds/tree.hpp (32 hunks)
✅ Files skipped from review due to trivial changes (2)
- hhds/tests/add_append_bench/chip_typical_long_tree_bench.cpp
- hhds/tests/traversal_bench/preorder_bench/chip_typical_long_tree_bench.cpp
🧰 Additional context used
🔇 Additional comments (8)
hhds/tests/chip_typical_long_correctness.cpp (2)
82-82: Verify the impact of reduced tree depth on test coverageThe tree construction depth has been reduced from 7 to 6. While this change might be necessary to accommodate the new packed 128-bit int representation for short pointers (as mentioned in the PR objectives), it's important to ensure that this reduction doesn't compromise the test coverage.
Please confirm that:
- The reduced depth is sufficient to test all aspects of the new short pointer implementation.
- The test still covers edge cases and potential issues that might arise in deeper trees.
If needed, consider adding additional test cases or modifying other parameters (like the number of children per node) to maintain comprehensive test coverage.
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1-150: Verify test coverage for new short pointer implementationWhile this test file has minimal changes, the PR objectives mention significant modifications to short pointers and the introduction of
num_occupied. It's crucial to ensure that this test still adequately covers the new implementation.Please confirm that:
- The test cases in this file still provide sufficient coverage for the new packed 128-bit int representation of short pointers.
- The
num_occupiedfunctionality is tested, either in this file or in other test files.- Any new edge cases or potential issues introduced by the changes are adequately tested.
Consider adding new test cases or modifying existing ones if necessary to ensure comprehensive coverage of the new implementation.
If you need help designing additional test cases or modifying existing ones to cover the new implementation, please let me know, and I'd be happy to assist.
hhds/tests/chip_typical_correctness.cpp (3)
104-104: Approved: Increased tree depth. Please clarify the rationale.The tree depth has been increased from 7 to 8, which will create a more complex tree structure for testing. This change seems beneficial for more thorough testing.
Could you please clarify the reason for increasing the depth? Is this related to the changes in short pointer implementation mentioned in the PR objectives?
132-135: Approved: Improved code readability.The addition of empty lines improves the code's readability by separating logical blocks.
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1-185: Please clarify the relationship between these changes and the PR objectives.The changes in this file primarily focus on enhancing the test coverage and result visibility. However, they don't directly implement or test the changes to short pointers mentioned in the PR objectives (changing explicit bit fields to a packed 128-bit int).
Could you please explain how these test modifications relate to the short pointer implementation changes? Are there any specific aspects of the new implementation that these enhanced tests are designed to verify?
hhds/tree.hpp (3)
57-58: Ensure that updatedCHUNK_BITSandSHORT_DELTAmaintain the 512-bit limitThe constants
CHUNK_BITSandSHORT_DELTAhave been updated to 50 and 18, respectively. According to the notes, the total size ofTree_pointersshould not exceed 512 bits. Please verify that these updates keep the total size within this limit.You can calculate the total bit size using the updated constants:
parent:CHUNK_BITS + CHUNK_SHIFTbitsnext_sibling:CHUNK_BITSbitsprev_sibling:CHUNK_BITSbitsfirst_child_l:CHUNK_BITSbitslast_child_l:CHUNK_BITSbitsnum_occupied:CHUNK_SHIFTbitsfirst_child_s: 128 bitslast_child_s: 128 bitsTotal bits =
(50 + 3) + 4 * 50 + 3 + 2 * 128 = 53 + 200 + 3 + 256 = 512bits.Since the total is 512 bits, the size limit is maintained.
84-100: Ensure correct bit manipulation in helper functionsThe helper functions
_get_first_child_s,_set_first_child_s,_get_last_child_s, and_set_last_child_sperform bit manipulation on the__int128variables. Carefully verify that the shift and mask operations correctly extract and set the desired bits without causing overlaps or data corruption.To verify the correctness, consider adding unit tests that cover edge cases, such as:
- Setting and getting values at the minimum and maximum indices.
- Using the minimum and maximum possible
Short_deltavalues.Would you like assistance in writing these unit tests or reviewing the bit manipulation logic in detail?
364-365: Use ofGImacro without proper contextThe
GImacro is used inget_datawithout a clear indication of what it expands to:GI(_check_idx_exists(idx), data_stack[idx].has_value(), "Index out of range or no data at the index");Confirm that the
GImacro is correctly defined and that it appropriately handles multiple conditions. Ensure that the macro provides meaningful error messages and does not suppress necessary checks.Would you like assistance in reviewing the definition of
GIor suggesting alternatives for clearer code?
| I(_check_idx_exists(first_child), "First child index out of range"); | ||
| I(_check_idx_exists(new_parent_id), "New parent index out of range"); | ||
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🛠️ Refactor suggestion
Incomplete or incorrect assertion messages
The assertions in _update_parent_pointer use the I macro with messages that may not provide sufficient context:
I(_check_idx_exists(first_child), "First child index out of range");
I(_check_idx_exists(new_parent_id), "New parent index out of range");Consider enhancing the assertion messages to include the actual values of first_child and new_parent_id to aid in debugging:
I(_check_idx_exists(first_child), "First child index out of range: " << first_child);
I(_check_idx_exists(new_parent_id), "New parent index out of range: " << new_parent_id);| __int128 first_child_s; | ||
| __int128 last_child_s; |
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Portability concerns with __int128 type
The use of __int128 for first_child_s and last_child_s may cause portability issues, as __int128 is a compiler-specific extension supported by GCC and Clang on certain architectures. This could limit the code's compatibility with other compilers or platforms.
Consider using a portable alternative, such as an array of uint64_t, to represent the 128-bit integers:
- __int128 first_child_s;
- __int128 last_child_s;
+ std::array<uint64_t, 2> first_child_s;
+ std::array<uint64_t, 2> last_child_s;Update the related methods to handle the new data structure appropriately.
Committable suggestion was skipped due to low confidence.
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There are conflicts that need to be solved before merging. |
SHORT_DELTAbits; instead.SHORT_DELTAbits.num_occupiedto directly get the total occupancy of a chunk.Summary by CodeRabbit