Re: How to calculate MD5 of huge files?

[Petite Abeille <petite.abeille@...>]

On Apr 22, 2010, at 12:49 PM, Jerome Vuarand wrote:

> local file = io.open(... or "bigfile.iso", "rb")
> while true do
> 	local chunk = file:read(16*1024) -- 16kB at a time
> 	if not chunk then break end
> 	evp:update(chunk)
> end

A bit off topic, but... out of curiosity, I was wondering about the use of 'while true do' + 'if not chunk then break' vs. 'while aChunk do' + 'aChunk = aFile:read()', e.g.:

-- using LHF's previous version of lmd5, the one before it was married to openssl :D
local sha1 = require( 'sha1' )
local aHash = sha1.new()
local aFile = assert( io.open( 'bigfile.iso', 'rb' ) )
local aChunk = aFile:read( 16384 ) 

while aChunk do
    aHash:update( aChunk )
    aChunk = aFile:read( 16384 )
end

Any reasons, aside from stylistic ones, to favor one form or another? I personally prefer an explicit conditional when using a 'while' clause, as I find it easier to comprehend, but I have noticed the above style quite often. Just curious :)

All things consider, I would rather use an iterator anyway, but perhaps that's just me:

local aReader = function() return aFile:read( 16384 ) end

for aChunk in aReader do
    aHash:update( aChunk )
end