Re: CRC in lua
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- Subject: Re: CRC in lua
- From: PA <petite.abeille@...>
- Date: 2006年6月16日 19:03:40 +0200
On Jun 14, 2006, at 17:05, Paul Hudson wrote:
The sl-exporters project on luaforge has an implementation of CRC32
http://luaforge.net/frs/?group_id=69
Cool :)
Here is the gist of it if someone is interested:
local CRC = {}
function CRC:table()
if self._table == nil then
local aTable = {}
local mod = bit.mod
local xor = bit.bxor
local rshift = bit.rshift
for anIndex = 0, 255 do
local aValue = anIndex
for _ = 1, 8 do
if mod( aValue, 2 ) == 1 then
aValue = xor( 0xEDB88320,
rshift( aValue, 1 ) )
else
aValue = rshift( aValue, 1 )
end
end
aTable[ anIndex ] = aValue
end
self._table = aTable
end
return self._table
end
function CRC:hash( aValue, aStart, anEnd )
local aTable = self:table()
local anHash = 0xFFFFFFFF
local band = bit.band
local xor = bit.bxor
local rshift = bit.rshift
for anIndex = ( aStart or 1 ), ( anEnd or aValue:len() ) do
anHash = xor( aTable[ band( xor( anHash, aValue:byte(
anIndex ) ), 255 ) ], rshift( anHash, 8 ) )
end
return xor( anHash, 0xFFFFFFFF )
end
It requires Reuben Thomas's bitlib module:
http://rrt.sc3d.org/Software/Lua/?page=Software/Lua
Cheers
--
PA, Onnay Equitursay
http://alt.textdrive.com/