crc32 v0.1.0

CRC-32/ISO-HDLC (the zlib/Ethernet variant).

Application scenarios

• Configuration blocks and firmware images.
• File or frame integrity where CRC-16 is too small.
• Compatibility with zlib, gzip, PNG, or Ethernet tools.

Contract

uint32_t crc32_update(uint32_t crc, uint8_t byte);
uint32_t crc32(const uint8_t *data, size_t length);

• Polynomial 0xEDB88320 (reflected 0x04C11DB7).
• Init 0xFFFFFFFF; final xor 0xFFFFFFFF.
• Check value for "123456789" is 0xCBF43926.
• Bitwise, no table, no allocation; crc32_update supports streaming.

Parameters

• This is the zlib variant; document it in the protocol.
• A 256-entry table trades 1 KB flash for speed.

Memory and timing

• 4 bytes of state; 8 XOR/shift steps per byte.

Integration

uint32_t crc = crc32(payload, length);
if (crc != expected) { reject(); }

When not to use

• A cryptographic check is required; use a MAC or hash.
• The peer uses CRC-32C (Castagnoli) or CRC-32/BZIP2; use the matching variant.

Verification

make test covers the standard check value, streaming, and empty input.

Behavior reference: zlib crc32.c (zlib license); this implementation is original.