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--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--
-- file: VFS_GetFileChecksum.lua
-- brief:
-- author: jK
--
-- Copyright (C) 2007-2013.
-- Licensed under the terms of the GNU GPL, v2 or later.
--
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
if (not VFS.GetFileChecksum) then
function VFS.GetFileChecksum(file, _VFSMODE)
local data = VFS.LoadFile(file, _VFSMODE)
if (data) then
local datalen = data:len()/4 --// 'x/4' cause we use UnpackU32
local striplength = 2 * 1024 --// 2kB
if (striplength >= datalen) then
local bytes = VFS.UnpackU32(data,nil,datalen)
local checksum = math.bit_xor(0,unpack(bytes))
return checksum
end
--// stack is limited, so split up the data
local start = 1
local crcs = {}
repeat
local strip = data:sub(start,start+striplength)
local bytes = VFS.UnpackU32(strip,nil,strip:len()/4)
local checksum = math.bit_xor(0,unpack(bytes))
crcs[#crcs+1] = checksum
start = start + striplength
until (start >= datalen)
local checksum = math.bit_xor(0,unpack(crcs))
return checksum
end
end
end
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