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List:       lua-l
Subject:    Re: Lua 5.3 work1 Considering math.isinteger or type()
From:       Jay Carlson <nop () nop ! com>
Date:       2013-07-26 2:35:42
Message-ID: 44AA612C-FFC0-4089-A5A5-722E9CA49F64 () nop ! com
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On Jul 25, 2013, at 6:04 PM, Sean Conner wrote:

> It was thus said that the Great Jay Carlson once stated:
> > Which architecture is handing you userspace pointers outside
> > the range of precise 64-bit doubles? (Amusingly you even get additional
> > range if the pointers are 4-byte aligned.)
> 
> If you are asking what architecture am I receiving addresses that exceed
> 53 bits in size, I haven't fully checked, but I am doing work on some very
> beefy 64-bit SPARC boxes at work---I concider it well in the realm of
> possibility.

I just spent a couple hours looking for the SPARC T3-T5 implementation supplements to \
the V9/Oracle 2011 architecture and came up with nothing. Somebody's blog entry \
implies they did implement the entire 64-bit virtual address space; I'm a little \
skeptical, but the M5 supports 32 DIMM slots per processor socket, with 16G or 32G \
DIMMs, so that's an (allegedly) purchasable machine with 1T RAM per socket, with 32 \
sockets.

This is a NUMA architecture, so if you *did* want to use the million dollar machine \
to run a single (hopefully massively threaded) process, you'd need 45 bits of address \
space. 

The T2 has a 48-bit limit on virtual addresses. So that's 3*1.5 years of Moore's Law \
left for that old architecture. Precise, byte-aligned addresses represented in floats \
would seem to have 8*1.5 years left before real memory outpaced them (at least on \
Larry Ellison's home computer). Besides ASLR, there are a bunch of hacks which eat \
virtual address space faster than that ( http://ssdalloc.cs.princeton.edu ) but I \
dunno what CPUs are gonna do.

> -spc (Yeah, how many programs assumed the top 8 bits of a 32-bit address
> 	could be arbitrarily set during the 80s, early 90s?)

The Mac had this problem in spades, and there's a mea culpa on folklore.org about it. \
I don't remember the Amiga having this problem (aside from maybe Microsoft's awful \
AmigaBasic), but I bailed from the platform well before I could populate a machine \
with more than 16M.

I would guess most CPU architects remember 32-bit cleanliness on the Mac with a great \
deal of pain, since most architectures seem to mandate sign extension, keeping you \
from doing anything particularly naughty with that high byte.

Jay

[1]: 48M of L3 cache per socket, which is six Agenda VR3s worth of memory, or roughly \
the size of my first hard drive. 


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