Initial project import

tools/v/vlib/hash/crc64/interop/README.md

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+# CRC64 Interoperability Fixture
+
+This directory contains interoperability tests for the V `hash.crc64` module, cross-validating
+against reference implementations in C and Python.
+
+## Overview
+
+The fixture verifies that `hash.crc64` produces identical CRC-64-ECMA-182 checksums when:
+- Computing the same data in V, C, and Python
+- Operating on various input patterns (empty, binary, text, large payloads)
+
+This helps catch:
+- Bit-ordering errors
+- Polynomial table generation bugs
+- Byte-order issues
+- Implementation divergences
+
+## Files
+
+- `crc64_interop.vsh` - Main V interop checker script
+- `crc64_ref.c` - C reference implementation (auto-compiled)
+- `crc64_ref.py` - Python reference implementation
+
+## Running the fixture
+
+From the V repository root:
+
+```bash
+v run vlib/hash/crc64/interop/crc64_interop.vsh
+```
+
+## Test vectors
+
+The fixture tests 10 vector categories:
+
+1. **empty** - Zero-length input
+2. **single_a** - Single character 'a'
+3. **single_null** - Single null byte
+4. **text_123456789** - Standard test vector
+5. **text_hello_world** - Common greeting
+6. **all_zeros_16** - 16 zero bytes
+7. **all_ones_16** - 16 0xFF bytes
+8. **repeating_pattern** - 150 bytes of "abc" repeated
+9. **all_bytes** - All 256 byte values in sequence
+10. **large_payload** - 10000 bytes of "test data " repeated
+
+Each vector is checksummed by:
+- V: `hash.crc64.sum(data)`
+- C: compiled from `crc64_ref.c`
+- Python: `crc64_ref.py`
+
+## Polynomial
+
+All implementations use CRC-64-ECMA-182:
+- Polynomial: `0x42F0E1EBA9EA3693`
+- Initial value: `0x0000000000000000`
+- Final XOR: `0x0000000000000000`
+- Check value for `"123456789"`: `0x6c40df5f0b497347`
+
+## Prerequisites
+
+- V compiler (tested with current repo version)
+- GCC (to compile C reference)
+- Python 3 (for Python reference)
+
+## Expected output
+
+```
+Compiling C reference helper...
+Running cross-validation tests...
+OK: empty => 0x0000000000000000
+OK: single_a => 0x926a79e87a919f5d
+OK: single_null => 0xbd4a6ec89c7eaafb
+...
+=== Results ===
+Passed: 10
+Failed: 0
+Total:  10
+```
+
+## Troubleshooting
+
+If the fixture fails:
+1. Ensure `gcc` and `python3` are in PATH
+2. Check that `hash.crc64` module can be imported (`v -silent test vlib/hash/crc64/`)
+3. Manual check: `python3 crc64_ref.py checksum 313233343536373839` (should match C)