crc - CRC generator for ruby

This is a general CRC (Cyclic Redundancy Check) generator for ruby.

It is written by pure ruby with based on slice-by-eight algorithm (slice-by-16 algorithm as byte-order free and byte-alignment free).

Included built-in CRC modules are CRC-32, CRC-64-ECMA, CRC-64-ISO, CRC-16-CCITT, CRC-16-IBM, CRC-8, CRC-5-USB, CRC-5-EPC and many more.

Customization is posible for 1 to 64 bit width, any polynomial primitives, and with/without bit reflection input/output.

This library is slower than ×85+ of zlib/crc32, and slower than ×120+ of extlzma/crc32 on FreeBSD 10.3R amd64.

If you need more speed, please use crc-turbo.

Summary

package name: crc
author: dearblue (mailto:[email protected])
report issue to: https://osdn.jp/projects/rutsubo/ticket/
how to install: gem install crc
version: 0.3
release quality: technical preview
licensing: BSD-2-Clause
any parts are under Creative Commons License Zero (CC0 / Public Domain), and zlib-style License.
dependency gems: none
dependency external C libraries: none
bundled external C libraries: none

API Guide

This examples are used CRC-32 module. Please see CRC for more details.

Calcurate by direct
- CRC.crc32(seq, init = CRC::CRC32.initial_crc) => crc-32 integer (likely as Zlib.crc32)
- CRC.crc32.crc(seq, init = CRC::CRC32.initial_crc) => crc-32 integer (likely as Zlib.crc32)
- CRC.crc32.digest(seq, init = CRC::CRC32.initial_crc) => crc-32 digest (likely as Digest::XXXX.digest)
- CRC.crc32.hexdigest(seq, init = 0) -> crc-32 hex-digest (likely as Digest::XXXX.hexdigest)
- CRC.crc32[seq, init = 0, current_length = 0] -> crc-32 generator
- CRC.crc32.new(seq, init = 0, current_length = 0) -> crc-32 generator
Calcurate by streaming
- CRC.crc32[init = 0, current_length = 0] => crc-32 generator
- CRC.crc32.new(init = 0, current_length = 0) => crc-32 generator
- CRC.crc32#update(seq) => self (likely as Digest::XXXX.update)
- CRC.crc32#finish => crc-32 integer (likely as Digest::XXXX.finish)
- CRC.crc32#crc => crc-32 integer (same as CRC.crc32#finish)
- CRC.crc32#digest => crc-32 digest (likely as Digest::XXXX.digest)
- CRC.crc32#hexdigest => crc-32 hex-digest (likely as Digest::XXXX.hexdigest)
Example:
```
x = CRC.crc32.new     # => #<CRC::CRC32:00000000>
x.update "123"        # => #<CRC::CRC32:884863D2>
x.update "456789"     # => #<CRC::CRC32:CBF43926>
x.crc                 # => 3421780262
x.digest              # => "\xCB\xF49&"
x.hexdigest           # => "CBF43926"
```

Combine

CRC.combine(crc1, crc2, len2) => combined crc integer (likely as Zlib.crc32_comibne)
CRC#+(right_crc) => combined crc generator

Example-1:

CRC.crc32.combine(CRC.crc32("123"), CRC.crc32("456789"), 6) # => 3421780262

Example-2:

CRC.crc32["123"] + CRC.crc32["456"] + CRC.crc32["789"] # => #<CRC::CRC32:CBF43926>

Create customized crc module

CRC.new(bitsize, poly, initial_crc = 0, refin = true, refout = true, xor_output = ~0) => new crc module class

MyCRC32 = CRC.new(32, 0x04C11DB7)
MyCRC32.class                     # => Class
MyCRC32.hexdigest("123456789")    # => "CBF43926"
MyCRC32.new("123456789")          # => #<MyCRC32:CBF43926>

Calcurate arc-crc (EXPERIMENTAL)

CRC.acrc(pre, post = nil, want_crc = 0) => arc-crc byte string

a = "12"
c = "789"
wantcrc = 0xCBF43926
b = CRC.crc32.acrc(a, c, wantcrc)   # => "3456"
CRC.crc32[a + b + c]                # => #<CRC::CRC32:CBF43926>

See CRC::ModuleClass.acrc for more detail.

Built-in CRC modules

% ruby -rcrc -e 'puts CRC::MODULE_TABLE.values.uniq.map { |m| m.name }.join(", ")'

CRC-1, CRC-3-ROHC, CRC-4-INTERLAKEN, CRC-4-ITU, CRC-5-EPC, CRC-5-ITU, CRC-5-USB, CRC-6-CDMA2000-A, CRC-6-CDMA2000-B, CRC-6-DARC, CRC-6-ITU, CRC-7, CRC-7-MVB, CRC-7-ROHC, CRC-7-UMTS, CRC-8, CRC-8-CCITT, CRC-8-MAXIM, CRC-8-DARC, CRC-8-SAE, CRC-8-WCDMA, CRC-8-CDMA2000, CRC-8-DVB-S2, CRC-8-EBU, CRC-8-I-CODE, CRC-8-ITU, CRC-8-LTE, CRC-8-ROHC, CRC-10, CRC-10-CDMA2000, CRC-11, CRC-11-UMTS, CRC-12-CDMA2000, CRC-12-DECT, CRC-12-UMTS, CRC-13-BBC, CRC-14-DARC, CRC-15, CRC-15-MPT1327, Chakravarty, CRC-16, CRC-16-ARINC, CRC-16-AUG-CCITT, CRC-16-CDMA2000, CRC-16-DECT-R, CRC-16-DECT-X, CRC-16-T10-DIF, CRC-16-DNP, CRC-16-BUYPASS, CRC-16-CCITT-FALSE, CRC-16-DDS-110, CRC-16-EN-13757, CRC-16-GENIBUS, CRC-16-LJ1200, CRC-16-MAXIM, CRC-16-MCRF4XX, CRC-16-RIELLO, CRC-16-TELEDISK, CRC-16-TMS37157, CRC-16-USB, CRC-16-A, CRC-16-KERMIT, CRC-16-MODBUS, CRC-16-X-25, CRC-16-XMODEM, CRC-17-CAN, CRC-21-CAN, CRC-24, CRC-24-Radix-64, CRC-24-OPENPGP, CRC-24-BLE, CRC-24-FLEXRAY-A, CRC-24-FLEXRAY-B, CRC-24-INTERLAKEN, CRC-24-LTE-A, CRC-24-LTE-B, CRC-30, CRC-30-CDMA, CRC-31-PHILIPS, CRC-32, CRC-32-BZIP2, CRC-32C, CRC-32D, CRC-32-MPEG-2, CRC-32-POSIX, CRC-32K, CRC-32K2, CRC-32Q, CRC-32-JAMCRC, CRC-32-XFER, CRC-40-GSM, CRC-64-XZ, CRC-64-ECMA, CRC-64-WE, CRC-64-ISO

Environment variables for behavior

RUBY_CRC_NOFAST=0: Use "crc-turbo" if posible. When failure required, same as RUBY_CRC_NOFAST=1.
RUBY_CRC_NOFAST=1: Force use ruby implementation with slice-by-16 algorithm. Not used "crc-turbo".
RUBY_CRC_NOFAST=2: Switch to lookup table algorithm from slice-by-16 algorithm. Slower than about 52% (when CRC-32).
RUBY_CRC_NOFAST=3: Switch to reference algorithm from slice-by-16 algorithm. Slower than about 7% (when CRC-32).

About CRC.combine

CRC.combine is ported from Mark Adler's crccomb.c in https://stackoverflow.com/questions/29915764/generic-crc-8-16-32-64-combine-implementation#29928573.

arc-crc (EXPERIMENTAL)

(Written in japanese from here)

crc-0.3 にて、任意の CRC となるバイト列を逆算する機能が実験的に追加されました。

今のところは、reflect-input/output 限定となっています。

require "crc/acrc" にて、その機能が利用可能となります。

名前の由来は、arc-sin などの C 関数である asin と同様に、arc-crc => acrc となっています。

以下は使用例です。

文字列 "123456789????" を CRC32 した場合に 0 となるような、???? の部分を逆算する

require "crc/acrc"

seq = "123456789"
seq << CRC.crc32.acrc(seq)
p CRC.crc32[seq] # => #<CRC::CRC32:00000000>

文字列 "123456789????ABCDEFG" の、???? の部分を逆算する

require "crc/acrc"

seq1 = "123456789"
seq2 = "ABCDEFG"
seq = seq1 + CRC.crc32.acrc(seq1, seq2) + seq2
p CRC.crc32[seq] # => #<CRC::CRC32:00000000>

文字列 "123456789????ABCDEFG" を CRC32 した場合に 0x12345678 となるような、???? の部分を逆算する

require "crc/acrc"

seq1 = "123456789"
seq2 = "ABCDEFG"
target_crc = 0x12345678
seq = seq1 + CRC.crc32.acrc(seq1, seq2, target_crc) + seq2
p CRC.crc32[seq] # => #<CRC::CRC32:12345678>

独自仕様の CRC モジュールにも対応

require "crc/acrc"

seq1 = "123456789"
seq2 = "ABCDEFG"
target_crc = 0x12345678
MyCRC = CRC.new(29, rand(1 << 29) | 1)
seq = seq1 + MyCRC.acrc(seq1, seq2, target_crc) + seq2
p MyCRC[seq] # => #<MyCRC:12345678>

[EOF]