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:

v run vlib/hash/crc64/interop/crc64_interop.vsh

Test vectors

The fixture tests 10 vector categories:

empty - Zero-length input
single_a - Single character 'a'
single_null - Single null byte
text_123456789 - Standard test vector
text_hello_world - Common greeting
all_zeros_16 - 16 zero bytes
all_ones_16 - 16 0xFF bytes
repeating_pattern - 150 bytes of "abc" repeated
all_bytes - All 256 byte values in sequence
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:

Ensure gcc and python3 are in PATH
Check that hash.crc64 module can be imported (v -silent test vlib/hash/crc64/)
Manual check: python3 crc64_ref.py checksum 313233343536373839 (should match C)

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