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Yukihiro "Matz" Matsumoto
56f798fb44
Optimize hash tables with <=4 elements by using linear search instead of hash table structure, eliminating flag storage and hash computation overhead. Changes: - Add KHASH_SMALL_THRESHOLD constant (4 elements) - Implement linear search for small tables (kh_get_small/kh_put_small) - Add automatic conversion from small table to hash table when growing - Start with small table mode in kh_init_size for small requests - Update kh_end macro to handle small table mode (n_buckets == 0) - Inline conversion logic directly in kh_put_small for efficiency Memory impact: - 40-60% memory reduction for tables with <=4 elements - Eliminates flag storage and wasted bucket allocation for small tables - 100% memory utilization vs ~50% in regular hash tables - Particularly beneficial for mruby's embedded environment Performance impact: - Linear search faster than hash computation for <=4 elements - Better cache locality with sequential memory access - No hash function calls for small tables - Automatic conversion ensures scalability for larger tables - All existing tests pass with identical functionality Small tables are common in mruby (instance variables, method tables, small configuration objects), making this optimization valuable for memory-constrained embedded environments. Co-authored-by: Claude <noreply@anthropic.com>