# Implementation Plan

- [x] 1. Create cache module with core data structures
  - Create `src/cache.rs` module file
  - Define `CrcParamsCacheKey` struct with `width`, `poly`, and `reflected` fields
  - Implement `Debug`, `Clone`, `PartialEq`, `Eq`, and `Hash` traits for the cache key
  - Add module declaration to `src/lib.rs`
  - _Requirements: 1.1, 3.1, 3.2_

- [x] 2. Implement thread-safe cache storage
  - Define global cache using `std::sync::OnceLock<RwLock<HashMap<CrcParamsCacheKey, [u64; 23]>>>`
  - Implement `get_cache()` function to initialize and return cache reference
  - Add necessary imports for `std::collections::HashMap`, `std::sync::{OnceLock, RwLock}`
  - _Requirements: 1.3, 2.3_

- [x] 3. Implement cache lookup and storage functions
  - Create `get_or_generate_keys(width: u8, poly: u64, reflected: bool) -> [u64; 23]` function
  - Implement cache hit path with read lock and HashMap lookup
  - Implement cache miss path with key generation followed by write lock and storage
  - Add error handling for lock poisoning with fallback to direct key generation
  - _Requirements: 1.1, 1.2, 4.1_

- [x] 4. Add cache management utilities
  - Implement `clear_cache()` function for testing and memory management
  - Add proper error handling for all cache operations
  - Ensure all cache operations are best-effort with graceful degradation
  - _Requirements: 4.3_

- [x] 5. Integrate cache into CrcParams::new()
  - Modify `CrcParams::new()` in `src/structs.rs` to use `cache::get_or_generate_keys()`
  - Replace direct call to `generate::keys()` with cache lookup
  - Ensure all existing functionality remains unchanged
  - Verify that the function signature and behavior are identical
  - _Requirements: 1.1, 1.2, 5.1, 5.2, 5.3_

- [x] 6. Create comprehensive unit tests for cache functionality
  - Add tests to `src/cache.rs`
  - Write tests for cache key creation, equality, and hashing
  - Test cache hit scenarios (same parameters return cached keys)
  - Test cache miss scenarios (new parameters generate and cache keys)
  - Test that cached keys are identical to directly generated keys
  - _Requirements: 1.1, 1.2, 3.1, 3.2_

- [x] 7. Add thread safety tests
  - Write concurrent access tests using `std::thread`
  - Test multiple threads reading from cache simultaneously
  - Test read-write contention scenarios
  - Verify cache consistency under concurrent access
  - Test lock poisoning recovery behavior
  - _Requirements: 1.3_

- [x] 8. Create integration tests for CrcParams compatibility
  - Add tests to verify `CrcParams::new()` behavior is unchanged
  - Test that all existing CRC parameter combinations work correctly
  - Verify that cached and uncached results are identical
  - Test multiple `CrcParams` instances with same parameters use cached keys
  - _Requirements: 5.1, 5.2, 5.3_

- [x] 9. Add comprehensive error handling tests
  - Test cache behavior when locks are poisoned
  - Test memory allocation failure scenarios
  - Verify fallback to direct key generation works correctly
  - Test cache operations under memory pressure
  - _Requirements: 4.1, 4.2_

- [x] 10. Update existing tests to work with caching
  - Run all existing tests to ensure no regressions
  - Update any tests that might be affected by caching behavior
  - Ensure test isolation by clearing cache between tests if needed
  - Verify all CRC algorithm tests still pass
  - _Requirements: 5.1, 5.2, 5.3_

- [x] 11. Add documentation and finalize implementation
  - Add inline documentation for all new public and internal functions
  - Update module-level documentation
  - Add usage examples in code comments
  - Ensure all code follows existing project style and conventions
  - _Requirements: 5.3_