Skip to content

Latest commit

 

History

History
123 lines (99 loc) · 5.22 KB

README.md

File metadata and controls

123 lines (99 loc) · 5.22 KB
Raw

crcspeed

CRC be slow.

This make CRC be fast.

No original ideas, but original adaptations. Lots of shoulder standing.

This started out as a modified version of comment at http://stackoverflow.com/questions/20562546 then was made more extensible.

Features

  • CRC processing in 8-byte steps for CRC-64 (Jones) and CRC-16 (CCITT).
  • Generates CRCs with overhead of 1.5 CPU cycles per byte
  • Little endian and big endian support
    • big endian support hasn't been tested yet (because qemu-system-sparc hates me).
  • Test suite generates comparison for: bit-by-bit calculation, byte-by-byte calcuation (Sarwate / lookup table), and 8-bytes-at-once calculation. Results are reported with resulting CRCs, throughput, and CPU cycles per byte comparisons.

Usage

  • Use little endian CRCs:
    • crc64speed_init();
    • crc64speed(old_crc, new_data, new_data_length);
    • crc16speed_init();
    • crc16speed(old_crc, new_data, new_data_length);
  • Use native architecture CRCs:
    • crc64speed_init_native();
    • crc64speed_native(old_crc, new_data, new_data_length);
    • crc16speed_init_native();
    • crc16speed_native(old_crc, new_data, new_data_length);
  • Use custom CRC64 variant:
    • crcspeed64native_init(crc_calculation_function, uint64_t populate[8][256]);
      • crc calculation function takes (0, data, data_len) and returns crc64 as uint64_t.
      • populate is a lookup table _init populates for future lookups.
    • crcspeed64native(populated_lookup_table, old_crc, new_data, new_data_length);
  • Use custom CRC16 parameters:
    • crcspeed16native_init(crc_calculation_function, uint16_t populate[8][256]);
      • crc calculation function takes (0, data, data_len) and returns crc16 as uint16_t.
    • crcspeed16native(populated_lookup_table, old_crc, new_data, new_data_length);

Additionally, there are specific functions for forcing little or big endian calculations: crcspeed64little_init(), crcspeed64little(), crc64big_init(), crcspeed64big(), crcspeed16little_init(), crcspeed16little(), crc16big_init(), crcspeed16big().

Architecture

  • crcspeed.c is a framework for bootstrapping a fast lookup table using an existing function used to return the CRC for byte values 0 to 255. Lookups then use fast lookup table to calculate CRCs 8 bytes per loop iteration.
  • crc64speed.c is a ready-to-use fast, self-contained CRC-64-Jones implementation.
  • crc16speed.c is a ready-to-use fast, self-contained CRC16-CCITT implementation.
  • when in a multithreaded environment, do not run initialization function(s) in parallel.
  • for fastest CRC calculations, you can force the entire CRC lookup table into CPU caches by running crc64speed_cache_table() or crc16speed_cache_table(). Those functions just iterate over the lookup table to bring everything into local caches out from main memory (or worse, paged out to disk).
  • The CRC-16 lookup table is 4 KB (8x256 16 bit entries = 8 * 256 * 2 bytes = 4096 bytes).
  • The CRC-64 lookup table is 16 KB (8x256 64 bit entires = 8 * 256 * 8 bytes = 16384 bytes).

Benchmark

The Makefile builds three test excutables:

  • crc64speed-test just returns check values for two input types across all three internal CRC process methods (bit-by-bit, byte-by-byte, 8-bytes-at-once).
  • crc16speed-test returns check values for the same data, except limited to CRC16 results.
  • crcspeed-test has two options:
    • no arguments: return check values for crc64 and crc16 at the same time.
    • one argument: filename of file to read into memory then run CRC tests against.
      • If CRC results do not match (for each CRC variant), the return value of crcspeed-test is 1, otherwise 0 on success.
% make
    CC crcspeed-test
    CC crc64speed-test
    CC crc16speed-test
% ./crcspeed-test ~/Downloads/John\ Mayer\ -\ Live\ At\ Austin\ City\ Limits\ PBS\ -\ Full\ Concert-gcdUz12FkdQ.mp4 
Comparing CRCs against 730.72 MB file...

crc64 (no table)
CRC = ee43263b0a2b6c60
7.142642 seconds at 102.30 MB/s (24.18 CPU cycles per byte)

crc64 (lookup table)
CRC = ee43263b0a2b6c60
1.777920 seconds at 411.00 MB/s (6.02 CPU cycles per byte)

crc64speed
CRC = ee43263b0a2b6c60
0.448819 seconds at 1628.09 MB/s (1.52 CPU cycles per byte)

crc16 (no table)
CRC = 000000000000490f
7.413062 seconds at 98.57 MB/s (25.10 CPU cycles per byte)

crc16 (lookup table)
CRC = 000000000000490f
1.951917 seconds at 374.36 MB/s (6.61 CPU cycles per byte)

crc16speed
CRC = 000000000000490f
0.441418 seconds at 1655.38 MB/s (1.49 CPU cycles per byte)

License

All work here is released under BSD or Apache 2.0 License or equivalent.

Thanks

Thanks to Mark Adler for providing a readable implementation of slicing-by-8 in a stackoverflow comment.

Thanks for pycrc for saving me another month figuring out how to write CRC-64-Jones by hand.

Thanks to A PAINLESS GUIDE TO CRC ERROR DETECTION ALGORITHMS for providing so many details it was clear I should give up and not try to re-create everything myself.