Hacker's Delight

Ben Olmstead writes with the review below of Henry S. Warren's Hacker's Delight, which is not about tricking folks into providing sensitive information, but rather about how to cleverly manipulate computers into doing more work on their part with less work on yours. Read on for his brief review.

Hacker's Delight
author	Henry S. Warren Jr.
pages	320
publisher	Addison Wesley Professional
rating	Excellent
reviewer	Ben Olmstead
ISBN	0201914654
summary	Collected Tips & Tricks for Programmers

Hacker's Delight is an impressive compendium of clever tricks for programmers. Warren concentrates on micro-optimizations -- few of the tricks in this book operate on more than 3 or 4 words of memory -- and he displays an impressive knowledge of diverse computer systems in the process.

Who Should Read This Book

Hacker's Delight is hardcore in its presentation and subject matter. I would not recommend this for a beginning programmer -- to fully understand the material requires at least some knowledge of concepts such as Assembly and Machine languages. However, anyone who writes performance-critical software should read this book, even if they do not plan to write Assembly code, both to learn the tricks given, and to learn the concepts behind them.

What's Good

The book is organized into chapters where Warren presents related tricks. In each chapter, he presents a few tricks which perform related tasks -- for example, in Chapter 3, he presents tricks for rounding (up or down) to the next power of 2, rounding to a multiple of a known power of 2, and detecting power-of-2 boundary crossings (i.e., checking for page faults). For each trick, he discusses why it works, whether the technique is generally applicable, related tricks which might be better in specific situations, and where a trick might be used in the real world.

Warren keeps his discussion architecture-neutral, while noting optimizations and problems for specific architectures for specific tricks -- in the process, he displays a vast array of knowledge about specific processors, from 1960's mainframes to x86, MIPS, PPC, Alpha, and others. He also skims the surface of hardware-design issues in a few places -- for example, he devotes a page or two to explaining why computers use base 2 for arithmetic, and why this is the most efficient choice.

What's Bad

This is an extremely dense book, and there are sections which are difficult to understand. Furthermore, there are many tricks which, while interesting, would be difficult to apply to real-world applications, and use of these tricks does violate the Keep It Simple, Clock Cycles Are Cheap And Someone May Have To Understand Your Code philosophy which is harped upon so heavily (not without reason) in modern software design. However, someone writing a compiler or high-performance code may feel that the benefit outweighs the potential risk.

The Summary

If you want a better understanding of the hardware on which your code runs, or you need to squeeze clock cycles, or you just enjoy seeing clever tricks, this is an excellent book. If you primarily use high-level languages such as VB, perl, python, etc., this may not be the right book for you. Be prepared for very dense material.

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Sounds like an interesting read...

Almost as interesting as those lovely discrete math textbooks were. This sounds more like 'Optimizer's Delight.'

To be honest, 'Hacker's Delight' sounded more like a cookbook title.

omg

i said a hip hop a hippie the hippie
to the hip hip hop, a you dont stop
a rock to the bang bang boogy say upchuck the boogy,
to the rhythm of the boogity beat.

now what you hear is not a test, i'm hacking to the motherfuckin beat
and me, rob malda, and the rest are gonna try and move your feet
see i am timothy and i'd like to say hello
to the ACs, freaks, and logged-in kooks, and all the goatse trolls
but first i gotta bang bang the boogie to the boogie
say up jump the boogie to the bang bang boogie
let's rock, you dont stop
rock the rhythm that will make your body rock
well so far youve heard my voice but i brought two friends along
and next on the mike's my man hemos
come on, hem, sing that song

Dubious value?

Furthermore, there are many tricks which, while interesting, would be difficult to apply to real-world applications.

Maybe you should break open the old CS textbook instead. IMO, learning general principles would be a much better use of your time.

Re:Dubious value?

Seriously depends what you're doing. If you're writing the next entreprise application, sure, optimization tricks are not really your main concern... If you're writing a game engine, though...

I remember back when I was younger and had much more free time (*longing sigh*) I spent most of a term and a summer writing a 3D wolfenstein-like engine, mostly under the careful instruction of a book: Tricks of the game programming gurus [amazon.com]. The book was great, and though it gave some optimizing ideas here and there the resulting engine was very slow (esp. compared to the wolf3d engine, which was so perfectly smooth... and the engine I made didn't even do monsters and doors and items). So then I turned to another book I had, called "PC Interdit", which was written in french and oriented towards Pascal rather than C which I was using, but explained a number of optimization tricks which made all the difference (examples: page flipping in mode X instead of double-buffering in mode 13h, basics of coding fast assembler functions to optimize C functions, etc). Before using that book's advice, my engine would run at something like 10 fps or so on my 486DX4 100Mhz in turbo mode, and 1fps more or less without turbo mode... After the optimizations, it ran very smoothly in turbo mode and at least 5-6fps in non-turbo.

So if you're programming a game engine, those books are really really useful. Or in fact if you're programming anything where squeezing every tiny bit of performance is critical. If you're programming a J2EE servlet engine, though, then for sure, it's a waste of your time.

Daniel

The author..

I know the author well. Here's some background for you slashdotters who may doubt his expertise:

Henry S. Warren, Jr., has had a forty-year career with IBM, spanning from the IBM 704 to the PowerPC. He has worked on various military command and control systems and on the SETL project under Jack Schwartz at New York University. Since 1973 he has been with IBM's Research Division, focusing on compilers and computer architectures. Hank currently works on the Blue Gene petaflop computer project. He received his Ph.D. in computer science from the Courant Institute at New York University.

Hacker delight....

...is the exact oposite of afternoon delight, I would imagine.

Sugar Hill Gang, anyone?

I said a hip, hop, hippy, hippy to the hip hop hacking you don't stop a hacking until the bang bin boogie said backslash the boogie to the rhythm of the boogity beat..

What you hear is not a test, I'm hacking to the beat. And me, the compiler, and my code are gonna start to move your screen.

See, I am das MB and I'd like to say hello
To the linux loners and the mac fairys and the losers on windows.

But first I gotta..bang slash bin slash P E R L said hack kernel yes hack hack the kernel until the whole machine runs like hell.

Proper.

Refreshingly different for the CS bookshelves

This is a great book for those looking to expand thier minds beyond the usual low-level-phobic computer science pulp. I do not employ any of the book's teqniques in my code, but I'm glad to know of them.

Sounds cool

Sounds like he knows his stuff. The world needs more asm-aware programmers. High level languages and all the trickery that is "keep the source simple, waste the abundant cycles" and all are important things. The problem IMHO is that these are techniques to be applied by a fully-fledged programmer, who is capable of doing it the hard way in C or even asm - but too many modern programmers have only ever know the world of OO languages. The Leaky Abstractions paper applies here too.

If you like this idea..

If you like this topic you may well appreciate this Assembly Language Gems Page [df.lth.se]

It's a little biased towards x86 assembly, but there are some neat tricks there, and some stunningly lovely code.

Recommended

I got this a couple of months ago and found it rather good -- If you are looking to shave a couple of cycles off you implementation of integer logarithms then have a look at it. I'd agree with the reviewer that it is rather dense, and you'll need to be numerate (graduate maths or C/S) to understand the algorithms, but not to find it useful. There are also quite a few amusing anecdotes from the author's time at IBM. Worth the cover price.

Jim Green

Base 2

...he devotes a page or two to explaining why computers use base 2 for arithmetic, and why this is the most efficient choice.

Why is that? I always figgered it had something to do with it being easier/cheaper to build hardware that only needs to store and detect 2 states (on/off) than multiple intermediate states.

Re:Base 2

Well, I remember when I was reading a book about assembler they expressed it beautifully by saying that if school taught kids binary numbers instead of the decimal system, the entire mathematics syllabus could be taught in a couple of months with time to spare.

Binary maths make many integer operations ridiculously simple, and while the fact that it's cheaper and more feasible to detect 2 states than 10 is true, there's also a certain simplicity that you can get to by coding everything with binary logical gates which wouldn't quite be there if you used some sort of decimal logical gates...

Basically, binary arithmetic is really simple so can be optimized really well and is much more universal, in the wider philosophical sense, than decimal arithmetic. Everything in the universe seems to revolve around a binary concept, rather than a decimal one... matter/antimatter, existence/non-existence, quantum spin states, etc.

Daniel

Definition of "Hacker"

I am pleased to see the correct use of the term "hacker". Now if we could just work on the folks at CNN...

Definitions, Titles, and Categorization

I noticed this book at the local Barnes and Noble. Unfortuately, it was (and still is) mis-catagorized and firmly stuck in the "Security" area of the technical / computer section.

Now I know that I'm toying with the usual hacker/cracker jihad. None the less, it seems the definition of "hacker" associated with secuirty is so engrained in to society that it manages to overcome even the content of the book itself. I would have thought the B&N folks, being in the book profession, would manage to catch this. Judging a book by its cover and all that (makes me wonder where a book called 'Pinky Fuzzy Bunnies' that studies furry erotica would land).

Of course, B&N are not the definitive measure of language. Where they stick a book doesn't go much beyond acknowledging one use of our much-flamed word. It doesn't negate the history of the word nor offer final proof of its popular definition. But it does show the power of that popular definition despite the obvious intent of the book's author.

Be it for good or not - there it is.

Efficiency != Portability (or overall goodness)

This sort of subject has been around for years, and gets rediscovered every so often, by a "new" generation of hackers. (Look, for instance, at the big deal made about Duff's Device [tuxedo.org] when C came along.) The problem is, that implementations of these ideas are often non-portable. (To other architectures, languages, or even the next version of the compiler.)

That's not to say that I don't enjoy reading about these clever things; there is a lot to be learned by studying this stuff. But implementing them is usually a mistake these days, if for no other reason than because there's already a portable way to do it which is probably more efficient. To go back to the Duff's Device example, almost all compilers will implement loop unrolling already. And that's a C-language trick, supposedly already a high-level language. Note I said supposedly! :-)

Be Wary

manipulate computers into doing more work on their part with less work on yours

To paraphrase the great Terry Pratchet: "Beware labour saving devices which are smaller than their manuals".

My computer won't work hard enough

I tried all kinds of tricks to get my computer to work harder. And whaddya know, one night it patched its speech software into the modem and called the union on me.

Ingrate! If it weren't for me, it'd be running gene sequences all day and night. Computers have no sense of perspective.

the most important thing

will it teach me how to hack Windows ME??? It's so hard -- I can't figure it out!

oh please

For 99% of people, these kinds of unreadable but "neat" optimizations are going to have no impact on execution time whatsoever. Good algorithm design and efficient architecture -- and yes, optimization, once you've profiled and located a bottleneck -- are worth far more than stupid bit shifting tricks, and your code will actually end up maintainable. If you follow the advice in this book, you're liable to produce code that looks like the Linux kernel.

Efficiency of base 2 arithmetic

explaining why computers use base 2 for arithmetic, and why this is the most efficient choice

I always thought that ternary computers [google.com] were theoretically more efficient, from a mathmatical point of view.

Hard to understand?

use of these tricks does violate the Keep It Simple, Clock Cycles Are Cheap And Someone May Have To Understand Your Code philosophy

In some cases, this may be true, but not always. If you want to increment a multiple-precision value, the textbook method is

int i, carry=1;

for(i=0;icarry+=x[i];
x[i]=carry;
carr y/=radix;
};

while the "cute trick" method is

int i=0;

while(++x[i]==0) i++;

The textbook method takes a while to recognize, just because it's very similar to many other loops; but the second is distinctive and can be recognized immediately. If I'm maintaining someon else's code, I'd much prefer to see the second.

Redundant and proud of it

In principal, I like the sound of this book. However, I have a shelf full of so-called 'secrets of the masters' books, each weighing in at around half a ton, containing 800 pages all stating the obvious. I look forward to hearing comments from those who have actually bought the thing.

If you want a better understanding of the hardware on which your code runs, or you need to squeeze clock cycles, or you just enjoy seeing clever tricks, this is an excellent book. If you primarily use high-level languages such as VB, perl, python, etc., this may not be the right book for you.

Time for me to state the obvious... I have worked on many applications that run uneccessarily slowly as a result of an accumulation of inefficient code. Sure, it is often better to sacrifice raw performance for portability, maintainabilty and plain readability, but code does not need to be obcure to be efficient. Optimisers take much of the hard work out of achieving this, but taking the time to examine compiler output once in a while will help you write high-level code in such a way as to give the optimiser room to strut it's stuff. If anything, there is often more to be gained by programs written in high-level languages (VB, perl, python, etc) if the coder takes time to examine the structure of his code and attempts to eliminate bottlenecks. Inefficiency is not a function of the development tools, it's a function of laziness.

Whoa!

3313 bytes in body

I almost thought that was 31337 or something!

And all this time

I thought that hacking was how to cleverly manipulate computers into doing more work on their part with way too much work on yours. Just get out of the house and fricken buy a skillet... no need to hack one up. [handyscripts.co.uk]

HACKMEM

HACKMEM is a document from the Elder Days at the MIT AI lab. It's not about optimisation, like Hacker's Delight, but it's full of lots of cool math/comp sci tidbits. I first discovered it back in the 80s when I was a script kiddie looking for cracking info (I hadn't understood the distinction between hacking and cracking at the time) and discarded it as lame. I revisited it about five years later after spending some time in the CS department and realised what a gem it really is.

Here's a sample:

ITEM 63 (Schroeppel, etc.):
The joys of 239 are as follows:

* pi = 16 arctan (1/5) - 4 arctan(1/239),
* which is related to the fact that 2 * 13^4 - 1 = 239^2,
* which is why 239/169 is an approximant (the 7th) of sqrt(2).
* arctan(1/239) = arctan(1/70) - arctan(1/99) = arctan(1/408) + arctan(1/577)
* 239 needs 4 squares (the maximum) to express it.
* 239 needs 9 cubes (the maximum, shared only with 23) to express it.
* 239 needs 19 fourth powers (the maximum) to express it.
* (Although 239 doesn't need the maximum number of fifth powers.)
* 1/239 = .00418410041841..., which is related to the fact that
* 1,111,111 = 239 * 4,649.
* The 239th Mersenne number, 2^239 - 1, is known composite, but no factors are known.
* 239 = 11101111 base 2.
* 239 = 22212 base 3.
* 239 = 3233 base 4.
* There are 239 primes < 1500.
* K239 is Mozart's only work for 2 orchestras.
* Guess what memo this is.
* And 239 is prime, of course.

HACKMEM [inwap.com]

Re:HACKMEM

If you have a minute, then, how does that work?

All prime factors of 2^p-1 are of the form 2kp+1 for some k. If we're looking for a factor, the obvious place to start is with k=1, which tells us that we should look at 2*239+1 = 479.

Now, 2^7 = 128, so
2^14 mod 479 = 98,
2^29 mod 479 = 2*98^2 = 48
2^59 mod 479 = 2*48^2 = 297
2^119 mod 479 = 2*297^2 = 146
2^239 mod 479 = 2*146^2 = 1

so 2^239-1 is a multiple of 479.

Premature optimisation is the root of all evil

I've not read the book yet, but I do have a general worry, that optimisation isn't always done in the right context or for the right reasons. Code that runs faster in a small test program can break when part of a larger program (by thrashing the cache for example). What's the point of optimising something that's seldom invoked, in other words, always ask an enthusiastic optimiser to show you their profiling results.

My favourite hacks are Jim Blinn's floating point tricks - 10% accurate square roots and reciprocals that blow away a floating point unit and are just what you need in graphics and games.

con.* files on NT or 2K, won't let you, try it

I just discovered the weirdest bug ever. I've tested it with NT4sp6 and win2Ksp2.

Try creating or renaming any file or your system to con.* * could be anything like .html .jpg .txt. The OS won't let you, it'll give an error. NT and 2K give different error mesasages. Under NT it just says the name is used already. Under 2K it says it's a reserved device name.

Karma whoring

I found some copies here. [amazon.com] I might get one.

Performance Critical

Shouldn't all software be built with performance in mind? Personally, I think that many developers have taken a love to today's high speed CPUs as it allows them to practically ignore performance issues. While it is true that in some areas performance tweaking is still vital, such as server software and high-end gaming, it seems that most mundane software, such as office tools and other nominal is over bloated and slow. Granted, it isn't as important, perhaps, but its still annoying when on my Dual Athlon machine I have speed issues, like when moving my media player causes the movie to stall and skip. I still chuckle at the popularity of Phoenix, an apparently slimmed down and tweaked browser. Even with fewer features then Mozilla, it stands on its own just because its fast. Does anyone else feel that programming in general today has been sloppy and aimed more at getting more features then having a fast, stable program?

Hey, that's one of my Christmas gifts!

The reviewer speaks truth about this book. It is quite dense and, in many cases, violates the "Code should be easily decoded by future programmers" rule.

I got this book for Christmas because I specifically asked for it. My mom was a bit put off by the title, though. The title refers to the original definition of "hacker," so don't get excited if you're all about computer security. There's nothing in there for you.

One of my favorite concepts in this book is the author's use of non-breaking code. As many of you know, the mechanism for sending instructions to the CPU requires a bit of quasi-premonition. Riddle your code with many if-, while-, and (the hideous) goto-statements, and you will end up with slow code due to the seemingly random jumps inside memory. Use some of the methods in this book, however, and you will end up with more efficient code in the longrun. Need I remind you of the speedup generated when you use non-breaking code within a lengthy while loop?

Hacker culture

I have come to despise the whole hacker culture based on the use of the sort of tricks the review illustrated. I comment my code like crazy, avoid confusing booleans, put null on the lhs of code, etc.

But unfortunately, the other people on my team do none of that, and it would only be more painful if they were trying the sort of stunts this book focuses on.

Shouldn't my compiler be reading this book?

I may be missing the point here... but, in todays software world, shouldn't I be worried about coding reliable, and easily read code?

And then let my compiler read through my code and determine the most efficient way to turn it into assembly? I mean, I would rather be multiplying by 2 rather than bitshifting; and then let my compiler turn it into whatever it needs to in order to run the fastest.

In fact, I really wouldn't be surprised if many of the better compilers already do most of these tricks for us, and we don't even know it.
But then again, I can't say for sure, since I have not read the book

Re:I've read this book

So, who are you? Rosie or Mike Blaszczak?

http://www.amazon.com/exec/obidos/tg/detail/-/0201 914654/ [amazon.com]

Doofus!

Left shift multiplies by a power of two - it doesn't round anything.

Re:I've read this book

If you actually have read this book, why are you plagiarizing Mike Blaszczak's Amazon review in a fairly unsubtle manner?

OK, it's good Slashdot Karma, but think what this is doing to your *real* karma -- much more of this and you're heading for reincarnation as a nematode worm ;-).

Re:Commodore 8-bit

Whoever modded this as a troll should be slapped. It is a legitimate question.