ExDataSketch.Binary.CRC (ExDataSketch v0.8.0)

CRC32C (Castagnoli polynomial, reflected, init 0xFFFFFFFF, xor-out 0xFFFFFFFF) — the checksum used by EXSK v2 frames.

CRC32C is the same checksum used by iSCSI, Btrfs, SCTP, and many storage systems. It is hardware-accelerated by Intel SSE 4.2 (CRC32 instruction) and ARMv8.1+ (CRC32CB/CRC32CH/CRC32CW/CRC32CX), so the Rust NIF version is essentially free on modern hardware.

Polynomial

Reversed polynomial: 0x82F63B78 (Castagnoli reflected)
Init value:          0xFFFFFFFF
Final xor:           0xFFFFFFFF
Reflect input/output: true

Stability

The CRC32C function is a well-specified standard. Output is identical across every implementation. The pure Elixir implementation and the Rust NIF implementation are property-tested for byte-identical agreement on random inputs.

Examples

iex> ExDataSketch.Binary.CRC.crc32c(<<>>)
0

iex> ExDataSketch.Binary.CRC.crc32c("123456789")
0xE3069283

Summary

Functions

check_vector()

Returns the standard CRC32C check vector ("123456789" -> 0xE3069283).

crc32c(bin)

Computes the CRC32C of the given binary.

pure_crc32c(bin)

Pure-Elixir CRC32C implementation. Never calls the NIF.

Functions

check_vector()

@spec check_vector() :: {binary(), non_neg_integer()}

Returns the standard CRC32C check vector ("123456789" -> 0xE3069283).

This vector is published by the CRC reference catalogue and matches every CRC32C implementation (iSCSI, Btrfs, SCTP, hardware CRC32 instruction).

Examples

iex> ExDataSketch.Binary.CRC.check_vector()
{"123456789", 0xE3069283}

crc32c(bin)

@spec crc32c(binary()) :: non_neg_integer()

Computes the CRC32C of the given binary.

Dispatches to the Rust NIF when available, falling back to a pure-Elixir table-driven implementation otherwise. Both implementations produce byte-identical output.

Examples

iex> ExDataSketch.Binary.CRC.crc32c(<<>>)
0

iex> ExDataSketch.Binary.CRC.crc32c("hello")
0x9A71BB4C

pure_crc32c(bin)

@spec pure_crc32c(binary()) :: non_neg_integer()

Pure-Elixir CRC32C implementation. Never calls the NIF.

Provided for parity testing and as the BEAM-only fallback.

Examples

iex> ExDataSketch.Binary.CRC.pure_crc32c("123456789")
0xE3069283