# Requirements Document

## Introduction

This feature adds a caching layer to the `CrcParams::new()` method to optimize performance when the same CRC parameters are used multiple times during program execution. Currently, each call to `CrcParams::new()` regenerates the folding keys through expensive mathematical operations, even when identical parameters have been used before. The caching system will store generated keys in memory and reuse them for subsequent requests with matching parameters, significantly improving performance for applications that create multiple CRC instances with the same configuration.

## Requirements

### Requirement 1

**User Story:** As a developer using the crc-fast library, I want CrcParams::new() to cache generated keys so that repeated calls with identical parameters don't regenerate keys unnecessarily.

#### Acceptance Criteria

1. WHEN CrcParams::new() is called with parameters that have been used before THEN the system SHALL return cached keys instead of regenerating them
2. WHEN CrcParams::new() is called with new parameters for the first time THEN the system SHALL generate the keys and cache them for future use
3. WHEN multiple threads call CrcParams::new() concurrently with the same parameters THEN the system SHALL handle thread safety correctly without data races

### Requirement 2

**User Story:** As a performance-conscious developer, I want the caching mechanism to have minimal overhead so that it doesn't negatively impact single-use scenarios.

#### Acceptance Criteria

1. WHEN CrcParams::new() is called for the first time with any parameters THEN the performance overhead SHALL be minimal compared to the current implementation
2. WHEN CrcParams::new() is called with cached parameters THEN the lookup SHALL be significantly faster than key generation
3. WHEN the cache is accessed THEN the lookup mechanism SHALL use efficient data structures optimized for the expected access patterns

### Requirement 3

**User Story:** As a developer working with custom CRC parameters, I want the cache to correctly identify identical parameter sets so that functionally equivalent calls are properly cached.

#### Acceptance Criteria

1. WHEN two CrcParams::new() calls use identical values for all parameters (name, width, poly, init, reflected, xorout, check) THEN the system SHALL treat them as cache hits
2. WHEN two CrcParams::new() calls differ in any parameter value THEN the system SHALL treat them as separate cache entries
3. WHEN parameter comparison is performed THEN the system SHALL use all relevant fields to determine cache key uniqueness

### Requirement 4

**User Story:** As a developer concerned about memory usage, I want the cache to have reasonable memory management so that it doesn't grow unbounded in long-running applications.

#### Acceptance Criteria

1. WHEN the cache stores parameter sets THEN it SHALL use memory-efficient storage for the cache keys and values
2. WHEN the application runs for extended periods THEN the cache SHALL not consume excessive memory for typical usage patterns
3. IF the cache grows large THEN the system SHALL provide a way to clear or manage cache size (though automatic eviction is not required for this initial implementation)

### Requirement 5

**User Story:** As a developer integrating this library, I want the caching to be transparent so that existing code continues to work without modifications.

#### Acceptance Criteria

1. WHEN existing code calls CrcParams::new() THEN it SHALL work exactly as before with no API changes required
2. WHEN CrcParams instances are created THEN they SHALL have identical behavior regardless of whether keys came from cache or generation
3. WHEN the caching system is active THEN it SHALL not affect the public interface or return values of CrcParams::new()