[fpc-pascal] Fast CRC functions?

[Bruno Krayenbuhl]

Quote :So you would not use this new crc32c() function to replace the zlib's
crc32() function, but as a convenient very fast hashing function at
application level.
For instance, our TDynArray wrapper will use it for fast items hashing.> 
hashing function at application level

Problem : does it exist on other processor architectures ?



An alternative if you dont need a standard CRC, for FPC internals. Needs to 
be retested by someone else.



What I dont know is if this algorythm would always give the EXACT same hash 
value on any processor. It is written in pure pascal so should be testable 
on various achitectures.



These are my timings calculating CRC and FNV Hash on a Win32 Dual-Core CPU.

Calculating CRC, FNVHash and SHA1 on file 
lazarus\1.3\lcl\include\wincontrol.inc rev. 45788



Compiled with -O3

CRC : 2 ms, 48 mus      CRC : 7df71ee1             unit fpccrc.pas

FNV : 619 mus             FNV : 54b39e30             unit uFnvHash32buf.pp

SHA1 : 3 ms, 318 mus                                     unit 
fpc-2.6.4\packages\hash\src\sha1.pp



CRC handles 1 complete buffer at the byte level

FNV handles 1 complete buffer at the DWORD level (Probably a problem with 
Endianness)



SHA1 handles streams and can be continued after intermediate results and of 
course returns a very long digest.
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