It still is a hobby for a lot of people, maybe a paid one. If you don't like writing code, don't. If you don't feel it is worthwhile to contribute to linux kernel, because other companies abuse the code then don't do it anymore. Abuse of a licence is an arbitrary thing and very very political one. Like in a swamp you can sink with your stern reasoning, just like a large rock. I'd say leave the politics to Mr. Stallman, he has been in that game for a long while.
I prefer binary drivers to no drivers at all. Having no binary drivers means no NDIS loader, no wireless support for alot of people. Like with company provided laptop for example made by acer i can still use wireless, because i can load windows driver. Personally i think from tech standpoint is coolest thing ever, because of tremendous code reuse. You don't have to write thousands of drivers. And thats where politics is so tricky. It is so easy to generate so much ill will poliking, then by just writing code and being servant of the people. Whoever they are.
Trying to fight corporations is useless unless you have a clear cut case where you can prove where they have broken the licence. Like say if they come out with "Boonix" thats a copy of Linux code with some modifications and completely different licence.
Linus has kept focus, that linux was, is and will be about technology and I agree with him on that. It is about providing wealth of options for software users. Not twisting their hand in very specific way. GPL protects linux kernel. Using GPL to blugeon other people's practices into extreme ways that GPL can be interpreted is silly. See there is new and old world. In the new world code is the law. In the old world it is legalese like licences, laws for real people from standpoint of non-technical point. To Linus GPL is only a way to protect kernel code, like a tool. Nothing political. Whereas for Mr Stallman it is his life and politics. For linus gnu toolkit and gcc, came with added protection of GPL. And gpl for him is exactly like a tool.
When you are a carpenter, you don't think of societal and humane implications of using auto-nailer to a hammer. Same with Linus, his codebase is what matters first. He is driving politics from within the kernel, you might say in very meritocratic way and not from GPL and how morally conflicting it is with GPL, to load binary drivers. GPL is a cover from blatant abuse of the kernel code.
Linus has kept focus since beginning of the project and I stand with him on that. He is a coder first, and likes to provide things and services for other fellow coders, not be meddeling in world of politics.
Private life, whatever it is of Mr Clinton is none of the press's business. I am sure there are more examples if you want to dig around. Same won't happen in europe. Job and sex life of a professional are two different to be evaluated on. As latter, should be left alone.
In religious freakout society, sex is taboo (still), so goes overreaction about it. Contrived motions to stop something from happening, usually cause greater harm as a whole, then positively contributing something positive to the society. IMO. 2c
In the beginning iTMS was sort of leagal fronting for getting "some" music, to get users going and rest can be gotten from elsewhere, cd collections, sharing sites, cd exchanging hands etc. From what I understand Jobs is all about hardware. Background of his, is in maintaing store that sold electronics parts, from junked equipment and new. If you read Jobs, software is important but only second to hardware. Music is soft item. He gets his jollies from selling hardware, so the foundation goes. Being the player to have, he can mark up some good profits. He can't wholly control pricing of music on itunes store, otherwise he'd lowered it. Its recording companies protecting their distribution channels, just in case. Paying a dollar for a song is like protecting delivery, store shelves, clerks from competing with net. Sort of chewing your own arm off, except you don't. (the good thing is that it allows for competition to make money as well, market is still open)
To me it is about litigating horse buggy whip back into agaist cars. I mean purists might say quality yadah-yadah, etc etc. But buyer is impulsive and with itms its all about impulsive buying. Just like ikea it gets expesive.
He doesn't care much about it, he can freak out, but not anywhere near as much as if sales on hardware lines were faltering. As well he doesn't control itms, records companies do, in terms of profit. So he can't really consider itms his baby, until he owns the whole process, like he did with Pixar and disney. 2c
From what I know of the Microsoft research, is that it is patent fishing net so that in the future they can sell/control techologies. Basically covering future turf, so that they can control cash flows and maybe make some money on top of it selling the patents. Control in such way if fooling company developing their product would have some nice feature that will partly infringe on the patent. Then microsoft can hurt the company and tell it what to do. And tech is developed far enough to have an idea for patent, and then dropped. Sort of like slugs sliming up the IP territory.
Simple: scan pci bus, save the footprint and characteristics, even ip adresses for fast boot. Then say if there is a new device on pci bus or any other bus, proceed with regular boot, otherwise read frozen image and viola.
It is a customer question driving back the point, that computers are way too complex today. You can say save image of just booted os, and keep booting it. And as soon as PCI resource will show up, you will need to perform long boot to get all things auto detected. I dunno, I think it is very valid question of the user. User gets what he asks and user is almost always right. People who are removed from the field whichevertronics, tend to ask questions that require thorough and very interrelated knowlege base. Not topological understanding, from standpoint of the designer.
So I think it is not a stupid question at all. It is a question of over time cruft growing over all sorts of desings, that causes this. And reiteration would be costly, but if consumers will pay for it, or refuse to buy slow booting sytems, the thats what they will get, fast booting systems.
It is already no hold bars release. And I'd rather them hold many bars, because it is so simple, elegant and easy to get things done, just right. I don't see them wanting to support os x word though, there isn't a point. With parralels allowing you to run windows, there isn't unbreakable barrier between you and windows version of word... which is of course hideous. I don't know why you'd need scripting in word documents. Since they are documents and not programs. 2c
Manufactured art stands for much of well sold pop(ular) music. Foundation of art is personal expression generated with somewhat limited amount of technological processes and external involvement. Saying that, many of big label "artists" are not in poisition to seek inner definition of what they think the song should potray(expression), but rather actuate (like robot arm) minds of the crew(out side of the band), to make music digestible. Given, huge artists like U2 et al, have their recording companies, they transcended the artist's beginnings into crass commercialists, whose product is still better then most of the manufactured artists but still contrived. So those "artists" are just like painters, like artistic kind, but approaching expression of painter that colors fences and appartments. Difference is subtle to common folk, but substantial when it comes to originality and unrepeatablility of the work produced. Foundation of the business, however is to make things reproducible in terms of art, so they can be sold many times, many copies each time.
I guess art stands itself apart from polishing process, art expression of inner. Musicians can't afford to make work like that, so they manufacture their recordings in order to make it digestible to most people. Which is fine. In some cases, lyrics can be said to be an artform, if there isn't any direct involvement of externalities, like i have described above. Song track isn't.
From what I know about bands, I think Phish is an artist band, in their definition, as they prefer to be live over distributing bits of plastic. They don't concern themselves with that too much (as far as i know). But these kinds of musicians are very few. And I don't listen to them, friends do.
What will help lowering amount of animosity in Washington DC, from what i gather from my highly unreliable sources is having representation, of the city in its own matters. People who live there.
"I do not mean this as an attack against your character in any way, but for you to portray knives as "much less lethal" belies an egregious ignorance in matters of self defense. A knife in even untrained hands can indeed be wholly lethal in a matter of seconds. It's quiet, doesn't run out of ammo, and is often far easier to conceal."
Ninjas never used guns, only smoking gun powder in escape.:)
There should be mandatory gun training and licencing, such way possibly misusers can be rated as such at earlier ages. Education of gun use, storage and respect would make for less accidents related to shooting. Respect, care and understanding of guns, I think should bring the amount of gun related violence. At least so I think. Often people who don't respect the car and road, do get in more accidents then those who don't(poor mans argument of analogy, sorry). Since 2nd amendment is so essential, in schools it should not be glossed over but rather taught and excersized like a freedom of speech. In controlled environment of course. In the end it will make country stronger. I am not in any way affiliated with gun industry, just a nerd north of the border. Constitution of the USA should be practiced and engrained into youngsters in every way possible, besides writing bullshit essays, why america is great. Since constitution is what made america great. Capitalism also, as white men relxed their control of such in post colonial times, but secondary to constitution.
Just talking to my girlfriend about blogging, she asks what is in that awful name too. Perhaps more elegant name shall be selected so masses can join in...
Criteria like that are hard to quantify, just don't let those who don't use patents, enforce them. If you haven't used it, and it is clear someone infringed on your patents, doing things their own way from scratch then tough luck. 2c
Womans freedoms seems the espouse woman's freedom from any responsibility for the children and gave them rights ownership of theirs. Sorry kiddo, looks like bad turn for you. My parents thankfully are old tradition type, my father DOES cook simple things. but he is the earner too. There isn't any wrestling for what and who is doing what. My mom mostly cooks and my father earns money. (The cult of "I" and egoism is what is driving that i think)
As for blackberries, i hate the damn things, though my family is very low tech but I do think if cop sees you punching a message he should take the baton and do it into couple of times into your neck, so you'd remember for sure for next few weeks what got you welts on your neck. I call it immediate imprinting.
Clearly you are bent on creating classes and layers within your society. People like you, protecting your investment without regards for general composition of the society, is what will drive united states into the ground. Thats large number of my friends have migrated to canada, away from deeply divided society of those who have and those who don't. Stolen a candy from the store when you're 14? Too bad, you will not have a white collar job. Been caught carrying around porno magazines in highschool? Good luck working anywhere you deal with people. Perhaps with jobs people have to give full justification why, after interview process, they aren't awarding the job. And if found out to be different, to be persecuted under similar set of rules as racial discrimination.
Reality companies aren't people and shall not have same rights as individuals, so harming the company isn't same as harming an individual. From that standpoint, I would hope that the guy recieves fair trial as to what was happening there. In reality, stopping stock traders from trading, is akin to stopping gamblers from gambling. If there is power loss in Las Vegas, power utility company will not carry damages to total of what is *POSSIBLY* have been earned by the company. In the end it is financial manipulations and not loss of real resources that is happening there.
As soon as it is one guy, the guy is bad. As soon as it is negligence on part of any other software company it is nothing. Come on, give me a break. If this guy goes into jail for this, I hope company has lost enough money to make its future infeasable. Clearly if one has so much control over resources of the company and he isn't paid what he expects to be, it is just asking for disaster. Partitioning and using secure systems, aka - unix and friends. The guy's are boneheads, some may say that they don't deserve this. But if they created the situation they should be taking the responsibility for it, not pushing it off onto one guy.
This article is a republishing of something I had up on my personal website a year or so ago before I joined Beyond3D, which is itself the culmination of an investigation started in April 2004. So if timeframes appear a little wonky, it's entirely on purpose! One for the geeks, enjoy. Origin of Quake3's Fast InvSqrt()
To most folks the following bit of C code, found in a few places in the recently released Quake3 source code, won't mean much. To the Beyond3D crowd it might ring a bell or two. It might even make some sense.
InvSqrt()
Finding the inverse square root of a number has many applications in 3D graphics, not least of all the normalisation of 3D vectors. Without something like the nrm instruction in a modern fragment processor where you can get normalisation of an fp16 3-channel vector for free on certain NVIDIA hardware if you're (or the compiler is!) careful, or if you need to do it outside of a shader program for whatever reason, inverse square root is your friend. Most of you will know that you can calculate a square root using Newton-Raphson iteration and essentially that's what the code above does, but with a twist. How the code works
The magic of the code, even if you can't follow it, stands out as the i = 0x5f3759df - (i>>1); line. Simplified, Newton-Raphson is an approximation that starts off with a guess and refines it with iteration. Taking advantage of the nature of 32-bit x86 processors, i, an integer, is initially set to the value of the floating point number you want to take the inverse square of, using an integer cast. i is then set to 0x5f3759df, minus itself shifted one bit to the right. The right shift drops the least significant bit of i, essentially halving it.
Using the integer cast of the seeded value, i is reused and the initial guess for Newton is calculated using the magic seed value minus a free divide by 2 courtesy of the CPU.
But why that constant to start the guessing game? Chris Lomont wrote a paper analysing it while at Purdue in 2003. He'd seen the code on the gamedev.net forums and that's probably also where DemoCoder saw it before commenting in the first NV40 Doom3 thread on B3D. Chris's analysis for his paper explains it for those interested in the base math behind the implementation. Suffice to say the constant used to start the Newton iteration is a very clever one. The paper's summary wonders who wrote it and whether they got there by guessing or derivation. So who did write it? John Carmack?
While discussing NV40's render path in the Doom3 engine as mentioned previously, the code was brought up and attributed to John Carmack; and he's the obvious choice since it appears in the source for one of his engines. Michael Abrash was mooted as a possible author too. Michael stands up here as x86 assembly optimiser extraordinaire, author of the legendary Zen of Assembly Language and Zen of Graphics Programming tomes, and employee of id during Quake's development where he worked alongside Carmack on optimising Quake's software renderer for the CPUs around at the time.
Asking John whether it was him or Michael returned a "not quite".
-----Original Message----- From: John Carmack Sent: 26 April 2004 19:51 Subject: Re: Origin of fast approximated inverse square root
At 06:38 PM 4/26/2004 +0100, you wrote:
>Hi John, > >There's a discussion on Beyond3D.com's forums about who the author of >the following is: > >float InvSqrt (float x){ > float xhalf = 0.5f*x; > int i = *(int*) > i = 0x5f3759df - (i>>1); > x = *(float*) > x = x*(1.5f - xhalf*x*x); > return x; >} > >Is that something we can attribute to you? Analysis shows it to be >extremely clever in its method and supposedly from the Q3 source. >Most people say it's your work, a few say it's Michael Abrash's. Do >you know who's responsible, possibly with a history of sorts?
Specifics of the way things are in russia, they'd try to sell you a fake one, in myriad of ways. Starting from distributors, fabricators and even legit factory might pack less medicine in then is written on the bottle. etc etc.
Well there are actually regulations forbidding competition in many areas, like priority given to companies to lay cable. So say you got 100mil in your pocket and you want to wire up a city. You would have to check with the regulations in that city and most likely they will forbid you to lay your communications, because there is already "a telecommunications company".
Like in toronto, only company allowed to lay fiber is bell, which is beyond me to understand, i can lay whatever the hell i like if I got permission from whoever owns the conduit. Apparently they will come down with order and snip your cable and remove it, without your permission. This braindamaged way about cable laying is not limited to United states.
I would second that as if there is no recourse offered, that what usualy east spirals down to. Thats where investment in india is far better then investment in china. See how they are handling Kashmir, it is tough. If it were for chinese. They'd come in, kill everyone who opposes them and jail the half of people to make the point. Thats the way the world turns.:)
As in rest of the world, what is india offers if foundation on which you can build, education and law that is derived from english systems, as some pointed out above. Once you get into the jig, its just one more of those things you hire smart people to deal with. Local people. It is something to be dealt with in the future of course to make shift from third world to second / first world country.\ 2c
Slashdot Mirror
It still is a hobby for a lot of people, maybe a paid one. If you don't like writing code, don't. If you don't feel it is worthwhile to contribute to linux kernel, because other companies abuse the code then don't do it anymore. Abuse of a licence is an arbitrary thing and very very political one. Like in a swamp you can sink with your stern reasoning, just like a large rock.
I'd say leave the politics to Mr. Stallman, he has been in that game for a long while.
I prefer binary drivers to no drivers at all. Having no binary drivers means no NDIS loader, no wireless support for alot of people. Like with company provided laptop for example made by acer i can still use wireless, because i can load windows driver. Personally i think from tech standpoint is coolest thing ever, because of tremendous code reuse. You don't have to write thousands of drivers. And thats where politics is so tricky. It is so easy to generate so much ill will poliking, then by just writing code and being servant of the people. Whoever they are.
Trying to fight corporations is useless unless you have a clear cut case where you can prove where they have broken the licence. Like say if they come out with "Boonix" thats a copy of Linux code with some modifications and completely different licence.
Linus has kept focus, that linux was, is and will be about technology and I agree with him on that. It is about providing wealth of options for software users. Not twisting their hand in very specific way. GPL protects linux kernel. Using GPL to blugeon other people's practices into extreme ways that GPL can be interpreted is silly.
See there is new and old world. In the new world code is the law. In the old world it is legalese like licences, laws for real people from standpoint of non-technical point. To Linus GPL is only a way to protect kernel code, like a tool. Nothing political. Whereas for Mr Stallman it is his life and politics. For linus gnu toolkit and gcc, came with added protection of GPL. And gpl for him is exactly like a tool.
When you are a carpenter, you don't think of societal and humane implications of using auto-nailer to a hammer. Same with Linus, his codebase is what matters first. He is driving politics from within the kernel, you might say in very meritocratic way and not from GPL and how morally conflicting it is with GPL, to load binary drivers. GPL is a cover from blatant abuse of the kernel code.
Linus has kept focus since beginning of the project and I stand with him on that. He is a coder first, and likes to provide things and services for other fellow coders, not be meddeling in world of politics.
Private life, whatever it is of Mr Clinton is none of the press's business. I am sure there are more examples if you want to dig around. Same won't happen in europe. Job and sex life of a professional are two different to be evaluated on. As latter, should be left alone.
In religious freakout society, sex is taboo (still), so goes overreaction about it. Contrived motions to stop something from happening, usually cause greater harm as a whole, then positively contributing something positive to the society. IMO.
2c
In the beginning iTMS was sort of leagal fronting for getting "some" music, to get users going and rest can be gotten from elsewhere, cd collections, sharing sites, cd exchanging hands etc. From what I understand Jobs is all about hardware. Background of his, is in maintaing store that sold electronics parts, from junked equipment and new. If you read Jobs, software is important but only second to hardware. Music is soft item. He gets his jollies from selling hardware, so the foundation goes. Being the player to have, he can mark up some good profits. He can't wholly control pricing of music on itunes store, otherwise he'd lowered it. Its recording companies protecting their distribution channels, just in case. Paying a dollar for a song is like protecting delivery, store shelves, clerks from competing with net. Sort of chewing your own arm off, except you don't. (the good thing is that it allows for competition to make money as well, market is still open)
To me it is about litigating horse buggy whip back into agaist cars. I mean purists might say quality yadah-yadah, etc etc. But buyer is impulsive and with itms its all about impulsive buying. Just like ikea it gets expesive.
He doesn't care much about it, he can freak out, but not anywhere near as much as if sales on hardware lines were faltering. As well he doesn't control itms, records companies do, in terms of profit. So he can't really consider itms his baby, until he owns the whole process, like he did with Pixar and disney.
2c
From what I know of the Microsoft research, is that it is patent fishing net so that in the future they can sell/control techologies. Basically covering future turf, so that they can control cash flows and maybe make some money on top of it selling the patents. Control in such way if fooling company developing their product would have some nice feature that will partly infringe on the patent. Then microsoft can hurt the company and tell it what to do. And tech is developed far enough to have an idea for patent, and then dropped. Sort of like slugs sliming up the IP territory.
I might be wrong, its been a while.
Simple: scan pci bus, save the footprint and characteristics, even ip adresses for fast boot. Then say if there is a new device on pci bus or any other bus, proceed with regular boot, otherwise read frozen image and viola.
It is a customer question driving back the point, that computers are way too complex today. You can say save image of just booted os, and keep booting it. And as soon as PCI resource will show up, you will need to perform long boot to get all things auto detected. I dunno, I think it is very valid question of the user. User gets what he asks and user is almost always right. People who are removed from the field whichevertronics, tend to ask questions that require thorough and very interrelated knowlege base. Not topological understanding, from standpoint of the designer.
So I think it is not a stupid question at all. It is a question of over time cruft growing over all sorts of desings, that causes this. And reiteration would be costly, but if consumers will pay for it, or refuse to buy slow booting sytems, the thats what they will get, fast booting systems.
It is already no hold bars release. And I'd rather them hold many bars, because it is so simple, elegant and easy to get things done, just right.
I don't see them wanting to support os x word though, there isn't a point. With parralels allowing you to run windows, there isn't unbreakable barrier between you and windows version of word... which is of course hideous. I don't know why you'd need scripting in word documents. Since they are documents and not programs.
2c
Manufactured art stands for much of well sold pop(ular) music. Foundation of art is personal expression generated with somewhat limited amount of technological processes and external involvement. Saying that, many of big label "artists" are not in poisition to seek inner definition of what they think the song should potray(expression), but rather actuate (like robot arm) minds of the crew(out side of the band), to make music digestible. Given, huge artists like U2 et al, have their recording companies, they transcended the artist's beginnings into crass commercialists, whose product is still better then most of the manufactured artists but still contrived.
So those "artists" are just like painters, like artistic kind, but approaching expression of painter that colors fences and appartments. Difference is subtle to common folk, but substantial when it comes to originality and unrepeatablility of the work produced. Foundation of the business, however is to make things reproducible in terms of art, so they can be sold many times, many copies each time.
I guess art stands itself apart from polishing process, art expression of inner. Musicians can't afford to make work like that, so they manufacture their recordings in order to make it digestible to most people. Which is fine. In some cases, lyrics can be said to be an artform, if there isn't any direct involvement of externalities, like i have described above. Song track isn't.
From what I know about bands, I think Phish is an artist band, in their definition, as they prefer to be live over distributing bits of plastic. They don't concern themselves with that too much (as far as i know). But these kinds of musicians are very few. And I don't listen to them, friends do.
2c
What will help lowering amount of animosity in Washington DC, from what i gather from my highly unreliable sources is having representation, of the city in its own matters. People who live there.
"I do not mean this as an attack against your character in any way, but for you to portray knives as "much less lethal" belies an egregious ignorance in matters of self defense. A knife in even untrained hands can indeed be wholly lethal in a matter of seconds. It's quiet, doesn't run out of ammo, and is often far easier to conceal."
:)
Ninjas never used guns, only smoking gun powder in escape.
There should be mandatory gun training and licencing, such way possibly misusers can be rated as such at earlier ages. Education of gun use, storage and respect would make for less accidents related to shooting. Respect, care and understanding of guns, I think should bring the amount of gun related violence. At least so I think. Often people who don't respect the car and road, do get in more accidents then those who don't(poor mans argument of analogy, sorry). Since 2nd amendment is so essential, in schools it should not be glossed over but rather taught and excersized like a freedom of speech. In controlled environment of course. In the end it will make country stronger. I am not in any way affiliated with gun industry, just a nerd north of the border. Constitution of the USA should be practiced and engrained into youngsters in every way possible, besides writing bullshit essays, why america is great. Since constitution is what made america great. Capitalism also, as white men relxed their control of such in post colonial times, but secondary to constitution.
Just talking to my girlfriend about blogging, she asks what is in that awful name too. Perhaps more elegant name shall be selected so masses can join in...
Criteria like that are hard to quantify, just don't let those who don't use patents, enforce them. If you haven't used it, and it is clear someone infringed on your patents, doing things their own way from scratch then tough luck.
2c
Womans freedoms seems the espouse woman's freedom from any responsibility for the children and gave them rights ownership of theirs. Sorry kiddo, looks like bad turn for you. My parents thankfully are old tradition type, my father DOES cook simple things. but he is the earner too. There isn't any wrestling for what and who is doing what. My mom mostly cooks and my father earns money. (The cult of "I" and egoism is what is driving that i think)
As for blackberries, i hate the damn things, though my family is very low tech but I do think if cop sees you punching a message he should take the baton and do it into couple of times into your neck, so you'd remember for sure for next few weeks what got you welts on your neck. I call it immediate imprinting.
Clearly you are bent on creating classes and layers within your society. People like you, protecting your investment without regards for general composition of the society, is what will drive united states into the ground. Thats large number of my friends have migrated to canada, away from deeply divided society of those who have and those who don't. Stolen a candy from the store when you're 14? Too bad, you will not have a white collar job. Been caught carrying around porno magazines in highschool? Good luck working anywhere you deal with people. Perhaps with jobs people have to give full justification why, after interview process, they aren't awarding the job. And if found out to be different, to be persecuted under similar set of rules as racial discrimination.
Reality companies aren't people and shall not have same rights as individuals, so harming the company isn't same as harming an individual. From that standpoint, I would hope that the guy recieves fair trial as to what was happening there. In reality, stopping stock traders from trading, is akin to stopping gamblers from gambling. If there is power loss in Las Vegas, power utility company will not carry damages to total of what is *POSSIBLY* have been earned by the company. In the end it is financial manipulations and not loss of real resources that is happening there.
As soon as it is one guy, the guy is bad. As soon as it is negligence on part of any other software company it is nothing. Come on, give me a break. If this guy goes into jail for this, I hope company has lost enough money to make its future infeasable.
Clearly if one has so much control over resources of the company and he isn't paid what he expects to be, it is just asking for disaster. Partitioning and using secure systems, aka - unix and friends. The guy's are boneheads, some may say that they don't deserve this. But if they created the situation they should be taking the responsibility for it, not pushing it off onto one guy.
http://www.penny-arcade.com/images/2002/20020930h. gif
Introduction
Note!
This article is a republishing of something I had up on my personal website a year or so ago before I joined Beyond3D, which is itself the culmination of an investigation started in April 2004. So if timeframes appear a little wonky, it's entirely on purpose! One for the geeks, enjoy.
Origin of Quake3's Fast InvSqrt()
To most folks the following bit of C code, found in a few places in the recently released Quake3 source code, won't mean much. To the Beyond3D crowd it might ring a bell or two. It might even make some sense.
InvSqrt()
Finding the inverse square root of a number has many applications in 3D graphics, not least of all the normalisation of 3D vectors. Without something like the nrm instruction in a modern fragment processor where you can get normalisation of an fp16 3-channel vector for free on certain NVIDIA hardware if you're (or the compiler is!) careful, or if you need to do it outside of a shader program for whatever reason, inverse square root is your friend. Most of you will know that you can calculate a square root using Newton-Raphson iteration and essentially that's what the code above does, but with a twist.
How the code works
The magic of the code, even if you can't follow it, stands out as the i = 0x5f3759df - (i>>1); line. Simplified, Newton-Raphson is an approximation that starts off with a guess and refines it with iteration. Taking advantage of the nature of 32-bit x86 processors, i, an integer, is initially set to the value of the floating point number you want to take the inverse square of, using an integer cast. i is then set to 0x5f3759df, minus itself shifted one bit to the right. The right shift drops the least significant bit of i, essentially halving it.
Using the integer cast of the seeded value, i is reused and the initial guess for Newton is calculated using the magic seed value minus a free divide by 2 courtesy of the CPU.
But why that constant to start the guessing game? Chris Lomont wrote a paper analysing it while at Purdue in 2003. He'd seen the code on the gamedev.net forums and that's probably also where DemoCoder saw it before commenting in the first NV40 Doom3 thread on B3D. Chris's analysis for his paper explains it for those interested in the base math behind the implementation. Suffice to say the constant used to start the Newton iteration is a very clever one. The paper's summary wonders who wrote it and whether they got there by guessing or derivation.
So who did write it? John Carmack?
While discussing NV40's render path in the Doom3 engine as mentioned previously, the code was brought up and attributed to John Carmack; and he's the obvious choice since it appears in the source for one of his engines. Michael Abrash was mooted as a possible author too. Michael stands up here as x86 assembly optimiser extraordinaire, author of the legendary Zen of Assembly Language and Zen of Graphics Programming tomes, and employee of id during Quake's development where he worked alongside Carmack on optimising Quake's software renderer for the CPUs around at the time.
Asking John whether it was him or Michael returned a "not quite".
-----Original Message-----
From: John Carmack
Sent: 26 April 2004 19:51
Subject: Re: Origin of fast approximated inverse square root
At 06:38 PM 4/26/2004 +0100, you wrote:
>Hi John,
>
>There's a discussion on Beyond3D.com's forums about who the author of
>the following is:
>
>float InvSqrt (float x){
> float xhalf = 0.5f*x;
> int i = *(int*)
> i = 0x5f3759df - (i>>1);
> x = *(float*)
> x = x*(1.5f - xhalf*x*x);
> return x;
>}
>
>Is that something we can attribute to you? Analysis shows it to be
>extremely clever in its method and supposedly from the Q3 source.
>Most people say it's your work, a few say it's Michael Abrash's. Do
>you know who's responsible, possibly with a history of sorts?
Not me,
Plus you can't sue grannies, dead people and wheel chair cancer boys by thousands generating millions upon millions of dollars.
Specifics of the way things are in russia, they'd try to sell you a fake one, in myriad of ways. Starting from distributors, fabricators and even legit factory might pack less medicine in then is written on the bottle. etc etc.
Well there are actually regulations forbidding competition in many areas, like priority given to companies to lay cable. So say you got 100mil in your pocket and you want to wire up a city. You would have to check with the regulations in that city and most likely they will forbid you to lay your communications, because there is already "a telecommunications company".
Like in toronto, only company allowed to lay fiber is bell, which is beyond me to understand, i can lay whatever the hell i like if I got permission from whoever owns the conduit. Apparently they will come down with order and snip your cable and remove it, without your permission. This braindamaged way about cable laying is not limited to United states.
I would second that as if there is no recourse offered, that what usualy east spirals down to. Thats where investment in india is far better then investment in china. See how they are handling Kashmir, it is tough. If it were for chinese. They'd come in, kill everyone who opposes them and jail the half of people to make the point. :)
Thats the way the world turns.
As in rest of the world, what is india offers if foundation on which you can build, education and law that is derived from english systems, as some pointed out above. Once you get into the jig, its just one more of those things you hire smart people to deal with. Local people. It is something to be dealt with in the future of course to make shift from third world to second / first world country.\
2c