×

Announcing: Slashdot Deals - Explore geek apps, games, gadgets and more. (what is this?)

Thank you!

We are sorry to see you leave - Beta is different and we value the time you took to try it out. Before you decide to go, please take a look at some value-adds for Beta and learn more about it. Thank you for reading Slashdot, and for making the site better!

Comments

top

How To Hijack Your Own Windows System With Bundled Downloads

mprinkey Re:Download from the source (324 comments)

Ninite.com is the only place I go for software on a new Windows installation. Select what you want and it gives you one installer. And you get exactly what you asked for. No search bars or crapware. It has been working great for years now.

about two weeks ago
top

Red Hat Engineer Improves Math Performance of Glibc

mprinkey Re:Lookup tables are faster and more accurate (226 comments)

But that was not my question. I fully understand how to use lookup tables/Chebyshev expansions of exp(x) and ln(x) to implement pow(x,a)--I have implemented these many times. My question was specifically on your assertion that any differentiable function could be evaluated with as a Newton-style iterative correction and thus provide arbitrarily precise results. I asked specifically to see how that is accomplished for pow(). There is no corrective mechanism in the algorithm you have stated above. The precision you get is a function of the precision that you've baked into your lookup table--and then it become the space/accuracy trade-off. On desktop/server CPUs, that trade-off is more often than not won by Chebyshev expansions, especially in a world of SSE/AXV vector instructions.

So, if there is a technique that does allow me to start with an initial guess x[0] of pow(a,b) and then create corrections of the form: x[i+1] = x[i] - f(x[i]) where f() uses only intrinsic math operations (+,-,*,/,etc) but not transcendentals, then I am quite anxious to see it.

about three weeks ago
top

Red Hat Engineer Improves Math Performance of Glibc

mprinkey Re:Lookup tables are faster and more accurate (226 comments)

With a table of values in memory you can also narrow down the inputs to Newton's method and calculate any differentiable function very quickly to an arbitrary precision. With some functions the linear approximation is so close that you can reduce it in just a few cycles.

No, you can't. I know this was done in Quake3 fastInvSqrt(), but that is the exception, not the rule in my experience. x = pow(a,b) is a differentiable function. How can you assemble a root function/Newton iteration to successively correct an initial guess for x to arbitrary precision--without actually calling pow() or other transcendental function? I have built Newton (and Halley and Householder) iterations to successively correct estimates for pow(a,b) when b is a particular rational number. You can re-arrange the root function to only have integer powers of the input a and of the solution value x, and those can be computed through successive multiplication. These can be fast, but they are certainly not useful when b is something other than a constant rational number. And even if the exponent value has only a few significant digits, the multiplication cascade starts to get expensive (that was the reason to use Halley/Householder because once you have f' calculated, f'' and f''' are almost free.)

If you know otherwise, please let me know. My current fast pow() function leverages IEEE floating point formats and Chebyshev polynomial expansions to get reasonable results. If there is way to polish an approximate pow() result with Newton (or higher order) iteration, I would be happy to learn it.

about three weeks ago
top

45% of U.S. Jobs Vulnerable To Automation

mprinkey Re:oblig (625 comments)

I don't think that the author got it all exactly right, but your points are wrong. Business is driven mindlessly by ONE THING--maximizing profitability. The time will come...and right soon...when machines will work well enough to eliminate many existing blue collar jobs and a large fraction of low-skilled white collar jobs too. There is and will be pushback, in the form of higher minimum wages and requirements for health insurances. And all those pushbacks do is accelerate the process. We can likely thank China, India, and Mexico for providing cheap labor and forestalling the onset of this mechanization a decade or two. Had they not been there to take our manufacturing jobs, serious automation efforts would have started even in the early 90s. As greed is the only acceptable (and fiduciarily mandated) corporate ethos, we should expect corps to follow its guiding light to its logical end. As soon as Walmart can stock their shelves with a robot, they will. As soon as McDonalds can reliably serve food without a single worker on staff, they will. As soon as Fedex can roll a Google truck, they will. Human labor is viewed as a "commodity" and it reliably becomes more expensive with time.

I think the mistake that the author makes is that he assumes humans will be part of the machine. They won't. There will be strikes and protests and maybe even legislation, but those will only slow the pace of change, not stop it. The US and Western European economies will look quite different in 50 years. I doubt anything but boutique items will be made even in part by humans. Before then, we will all have to ask ourselves what we do with our time and how do we provide for our needs. The end of the story effectively contrasts two possible outcomes.

about a year ago
top

More Encryption Is Not the Solution

mprinkey Re:quick key repetition (207 comments)

Replace the 100 million key dictionary with a PRNG seeded with a secret key, some time information, and source/destination ports and addresses. The NSA would have the PRNG, the key, and the seeding input from the packet. They could deduce the key without much effort and the keys would appear truly random to anyone without knowledge of the secret key, no matter the sample size.

about a year and a half ago
top

Making Your Datacenter Into Less of a Rabid Zombie Power Hog

mprinkey Re:Location Location Location (52 comments)

It is easier to just drill wells. Google geothermal heat pump.

about a year and a half ago
top

Motorola Developing Pill and Tattoo Authentication Methods

mprinkey How do you limit authentication?! (194 comments)

This idea is terrible. It is even worse than RFID credit cards. Since it has active electronics, I assume this is able to do challenge/response authentication, which is good. But how do you disable it? Somebody just "bumps" into you with a scanner and pays their dinner bill with your gut. At least RFID-chipped cards can be stored in a conductive pouch to prevent walk-by theft.

Whatever shape these new authentication methods take, they need to be at minimum:

(1) Challenge/Response based, and
(2) Momentary ON

Requirement 1 kills most biometrics systems. And Requirement 2 kills most implant/ingested systems.

about a year and a half ago
top

How Did You Learn How To Program?

mprinkey Re:Timex Sinclair 1000 (623 comments)

Yeah...TImex Sinclair 1000, a hand-me-down BW TV from my grandfather, and my old tape recorder. That was the beginning for me...back in 6th grade. I bought from Hills for $50, I think. I spend many hours on it...until the C64 and floppy drive came a few Christmas' later. I look back on those days and the oceans of free time I had...peeking and poking and disassembling code. I remember spending many hours typing in code from Compute! Gazette...that was all C64. And Transactor too.

about a year and a half ago
top

Ask Slashdot: Are There Any Good Reasons For DRM?

mprinkey Re:Art doesn't need remuneration (684 comments)

As machines and computers do more and more of the work, will such a thing as work, as we know it, still exist in 50 years ?

Fixed that for you. The answer is no. My child will live to a see a very different world and economic reality.

about 2 years ago
top

Ask Slashdot: Mathematical Fiction?

mprinkey Re:Neverness by David Zindell (278 comments)

This. The whole series is very well done and deeply engaging. But it is dense. It might be best described as fictional mathematical physics, but it is not your typical SF...even hard SF.

more than 2 years ago
top

Sinclair ZX Spectrum 30th Anniversary

mprinkey Re:My first computer (212 comments)

I had the Timex Sinclair 1000 as well, but not 16KB module. Paid $60 for it at Hills--I was in 6th grade. It learned quickly to be careful with my precious 2k of RAM, but I coded a fairly accurate image of the Space Shuttle and figured out how to make it "fly" across the screen. Hard to believe I have been writing code for almost 30 years!

more than 2 years ago
top

'Twisted' Waves Could Boost Capacity of Wireless Spectrum

mprinkey Re:*Orbital* angular momentum (147 comments)

I think the key take-away is that there is another physical signal dimension to exploit--frequency, directionality, polarization, and now orbital angular momentum. They have demonstrated that they can distinguish between two channels on the same frequency using orbital angular momentum as the differentiator. So, OAM mode can be added to the tool kit. If they can distinguish among a few dozen modes and still allow beam forming, this could provide a huge benefit for cellular and other wireless networks. If they can distinguish among hundreds or thousands of modes, it could be truly transformative. It has been a long time since my EM class, but I wonder if similar mode discrimination could be applied to waveguides.

more than 2 years ago
top

AMD: What Went Wrong?

mprinkey Re:Products (497 comments)

Sandy Bridge has fused multiply-add too.

more than 2 years ago
top

NVIDIA Launches GeForce GTX 560 Ti 448-Core GPU

mprinkey Re:fused off? Really?! (127 comments)

Probably referring to efuses that can be burned out on the die. These are common and allow CPU/GPUs to have unit-specific information (like serial numbers, crypto keys, etc) coded into otherwise identical parts from the fab. Video game systems like the 360 use them as an anti-hacking measure...disallowing older version of firmware to run on systems that have certain efuses "blown." Likely, there is an efuse for each core or group of cores. Those can be burned out if they are found to be defective or to simply cripple a portion of the part for down-binning. That is a practice at least as old as the Pentium 2.

more than 3 years ago
top

Which OSS Clustered Filesystem Should I Use?

mprinkey Re:Offsite backups (320 comments)

Truecrypting external USB/eSATA drives are by far the better option. We also use normal 3.5" drives with external USB/eSATA docks. There are NO cheap tape solutions anymore. I'd further argue that what tape solutions exist are trumped by hard drive backup solutions for on-site backup--far slower and no more reliable than hard drives. Tape is dead. Anyone still using them is either leveraging a 5-to-10-year-old investment in a tape robot or is being sold a bill of goods by a vendor.

more than 3 years ago
top

Looking Back On a Year of LibreOffice

mprinkey Re:It feels too heavy and old (242 comments)

I have to agree about the heft. But I prefer the "old" style interface. I had to install Office 2007 to interact with some clients and I am completely lost. I've been using word processors since the C64 days, but this is the first time I decades that I have stared blankly at a program and had to click on every menu/button/active splotch trying to find out how to turn on Track Changes.

Of course, people can get used to the interface and maybe following the mythical transition, I will be enamored with its interface glory. But it just seems different for difference's sake...like .docx and .xlsx where.

To the LibreOffice folks, you really need to do a top-down performance/memory analysis. I like it and will continue to use it, but I don't see why it needs to be the resource hog it is.

more than 3 years ago
top

Ask Slashdot: Clusters On the Cheap?

mprinkey Re:How many commenters have BUILT a cluster!? (264 comments)

The difference is even bigger than you posted! You made a math error on the Sandy Bridge FLOP calculation:

64 Sandy Bridge Cores: 8 FLOPS/Hz * 2.8 GHz * 64 cores = 1433.6 GFLOPS

48 Magny Cours: 4 FLOPS/Hz * 2.1 GHz * 48 cores = 403.2 GFLOPS

So, Sandy Bridge is roughly 3.5 times faster than AMD.

And the original poster commented that the application was parceling out data sets and crunching on the independently, so the application is embarassingly parallel. This design would be rubbish for any *real* parallel application, but I think it is optimal for OP's stated goal.

more than 3 years ago
top

Ask Slashdot: Clusters On the Cheap?

mprinkey How many commenters have BUILT a cluster!? (264 comments)

OK, I won't be too hard on the discussions above, but I read enough to try to give some real help to the OP. I get that this is basically an embarrassingly parallel application. So, that means a gigabit network is fine. That also means that single core performance is the ONLY indicator of the speed of the application. That means investing in anything AMD is a mistake. The best bang for the buck is quad-core Sandy Bridge CPUs. 4000 pounds is about $6300. I can build a quad-core 2.8 GHz Sandy Bridge node (2GB/core in a desktop case) for under $400 each. Cables, Gbit switch, and 15-16 nodes (60-64 Sandy Bridge cores total) will fit in the budget without too much effort.

OK...so, it isn't ECC memory. And it isn't general purpose. And it isn't going to run most parallel applications worth a crap due to the gbit network, but the point of building a cluster is to design it to match the application. 64 Sandy Bridge cores will run rings around any Magny Cores solution you can build for the same price.

more than 3 years ago
top

Age Bias In IT: the Reality Behind the Rumors

mprinkey Re:C programmers? Wanted! (582 comments)

FORTRAN is not that uncommon, particularly among engineers.

more than 3 years ago

Submissions

mprinkey hasn't submitted any stories.

Journals

mprinkey has no journal entries.

Slashdot Login

Need an Account?

Forgot your password?