Re: Bug in string.unpack
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- Subject: Re: Bug in string.unpack
- From: cherue <cherue.lual@...>
- Date: 2020年3月12日 19:06:36 +0100
On Thu, Mar 12, 2020, at 6:53 PM, dyngeccetor8 wrote:
> On 12/03/2020 20.06, cherue wrote:
> > Hello,
> >
> > I found a bug in string.unpack:
> >
> > ```
> > Lua 5.3.5 Copyright (C) 1994-2018 Lua.org, PUC-Rio
> >> string.unpack("I4", "255円255円255円255円")
> > 4294967295 5
> >> string.unpack("I8", "255円255円255円255円255円255円255円255円")
> > -1 9
> >> string.unpack("I8", "255円255円255円255円255円255円255円127円")
> > 9223372036854775807 9
> >> string.unpack("I8", "255円255円255円255円255円255円255円128円")
> > -9151314442816847873 9
> > ```
> >
> > I tried looking for the cause but I am not fluent in C. Maybe something about lua_Integer?
> >
>
> So where is the bug?
>
> In my point of view you've got quite consistent results
> for two's-complement little-endian integer encoding.
>
> -- Martin
I should have gone into more detail, sorry.
The documentation on format strings includes:
- i[n]: a signed int with n bytes (default is native size)
- I[n]: an unsigned int with n bytes (default is native size)
So string.unpack("I8", "255円255円255円255円255円255円255円255円")
should be an unsigned integer with value 18446744073709551615.