Re: Use of math.huge on 64bit Linux
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- Subject: Re: Use of math.huge on 64bit Linux
- From: Sean Conner <sean@...>
- Date: Wed, 5 Mar 2014 17:21:39 -0500
It was thus said that the Great Sean Conner once stated:
>
> Okay, I'm using Lua 5.1.5 (and all the patches [1]) and for the life of
> me, I can't figure out what I'm doing wrong.
I have figured out what I'm doing wrong. And yes, it is an issue with
64bit Linux (or 64b systems in general). The problematic bit of code first:
lua_Number ival;
if (lua_isnumber(L,3))
ival = lua_tonumber(L,3);
/* SNIP */
if (ival >= RLIM_INFINITY)
ival = RLIM_INFINITY;
limit.rlim_cur = ival;
This gets translated to:
lua_Number ival;
if (lua_isnumber(L,3))
ival = lua_tonumber(L,3);
/* SNIP */
if (ival >= ((unsigned long int)(~0UL)))
ival = ((unsigned long int)(~0UL));
limit.rlim_cur = ival;
On the 64bit system in question, an unsigned long is 64 bits in size. But
ival is of type double (ultimately). But, only integer quantities up to
2^53 (or is it 2^52? It's somewhere around that range) are safely stored as
integers in doubles, so the line
limit.rlim_cur = ival;
is the problem! The value in ival isn't representable as an integer (well,
techinically, it is on a 64-bit system, but a double can only store integers
up to 2^53 (or thereabouts)) the value of 0 is stored into limit.rlim_cur,
thus the root cause of the problems I've been fighting for the past two
days.
Sigh.
Now that I know the issue, I can fix the bug.
-spc