|WARNING| net/crc: use static constants for SSE42 PCLMULQDQ parameters

[dpdklab at iol.unh.edu]

Test-Label: ai-code-review
Test-Status: WARNING
https://dpdk.org/patch/172730

_AI Code Review_

=== Patch Review: series.patch (via Claude) ===
Review date: 2026-11-08

# DPDK Patch Review

## ERRORS

None identified.

## WARNINGS

**1. Removed `rte_net_crc_sse42_init()` function body may break ABI**

The function `rte_net_crc_sse42_init()` is now an empty stub. If this function is part of the public API (exported symbol), removing its functionality could break applications that call it, even though the runtime behavior might still be correct due to static initialization.

**Suggested fix:** Check if `rte_net_crc_sse42_init()` is exported. If it is, mark it as deprecated and document in release notes that it's now a no-op. If it's internal-only, consider removing it entirely.

**2. Missing release notes update**

This patch changes the implementation approach from runtime initialization to compile-time initialization, which is a performance improvement and a change in when initialization occurs. This should be documented in release notes.

**Suggested fix:** Add a note to `doc/guides/rel_notes/release_XX_YY.rst` (current release) documenting the change:
```rst
* **net/crc: optimized SSE42 initialization.**

  CRC folding constants are now compile-time initialized rather than
  runtime initialized, eliminating the need to call ``rte_net_crc_sse42_init()``.
```

## INFO

**1. Array element order convention**

The uint64_t arrays are populated with elements in `[k1, k2]` order, matching the original `_mm_set_epi64x(k2, k1)` behavior. The SIMD load (`_mm_load_si128`) loads in little-endian order, so array index 0 is the low 64 bits. The `_mm_set_epi64x(high, low)` intrinsic places its first argument in the high 64 bits, so the transformation from `_mm_set_epi64x(k2, k1)` to array `{k1, k2}` is correct. This is not an issue, just noting the implicit endianness dependency is preserved.

**2. Alignment attribute placement**

The struct uses `__rte_aligned(XMM_SIZE)` on the type definition, and the static const instances inside the handler functions will inherit this alignment. This is correct. Note that `XMM_SIZE` is typically 16, matching the original `alignas(16)` on the old global variables.

Review-Result: WARNING