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# c2e1d09047db oxygen / vendor / crc-fast / .kiro / specs / crc-width32-shared-base / prompt.md
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CRC Width-32 Shared Base Refactoring

Goal

Refactor the CRC-16 and CRC-32 algorithm implementations to share a common base, reducing code duplication and preparing for future CRC width additions (like CRC-8).

Background

CRC-16 computation is performed by scaling 16-bit values to 32-bit space, using the CRC-32 algorithm infrastructure, and then scaling the result back to 16 bits. This means CRC-16 and CRC-32 share nearly identical implementations for:

  • process_0_to_15() function (~100 lines each, nearly identical)
  • load_constants() - identical constants
  • fold_16() - identical logic
  • fold_width() - identical logic
  • barrett_reduction() - nearly identical (just different final extraction)
  • create_coefficient() - identical
  • perform_final_reduction() - identical
  • get_last_bytes_table_ptr() - identical

Approach

Create a shared module (src/crc32/width32_ops.rs) containing the common 32-bit-space operations that both CRC-16 and CRC-32 use. The Width16 and Width32 trait implementations will delegate to these shared functions, with Width16 performing the final 16-bit extraction where needed.

Constraints

  • Must maintain full backwards compatibility with existing CRC-16, CRC-32, and CRC-64 functionality
  • All existing tests must continue to pass
  • The refactoring should make it easier to add future CRC widths (like CRC-8)