Ask General Programming Questions Not Worth Their Own Thread

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > Ask General Programming Questions Not Worth Their Own Thread

«‹›672 »

Vulture Culture: Jul 14, 2003; I was never enjoying it. I only eat it for the nutrients.

Completely not a question, but holy Christ, Erlang's list comprehensions make Python's list comprehensions look like for loops and I had to post somewhere.

# ? Jun 26, 2011 05:25

Adbot: ADBOT LOVES YOU

# ? Jun 9, 2024 06:01

TasteMyHouse: Dec 21, 2006

Misogynist posted:

Completely not a question, but holy Christ, Erlang's list comprehensions make Python's list comprehensions look like for loops and I had to post somewhere.

I think the word "for" in the python list comps makes them look like for loops

# ? Jun 26, 2011 05:38

ultrafilter: Aug 23, 2007; It's okay if you have any questions.

Is there already a thread on Amazon web services? I'm beginning to play around with some of their stuff, and it sure would be nice to have one.

# ? Jun 28, 2011 00:05

Vulture Culture: Jul 14, 2003; I was never enjoying it. I only eat it for the nutrients.

I'm suddenly really interested in functional programming languages and am already learning Erlang, OCaml and Haskell. What's Scala good at?

# ? Jun 28, 2011 03:39

Plorkyeran: Mar 22, 2007; To Escape The Shackles Of The Old Forums, We Must Reject The Tribal Negativity He Endorsed

Misogynist posted:

What's Scala good at?

Being less lovely than Java when you have to run on the JVM for whatever reason.

# ? Jun 28, 2011 03:57

Acer Pilot: Feb 17, 2007; put the 'the' in therapist

I'm writing a program that converts an image into a JPEG. It turns it from RGB to YUV, then does a 4:2:0 chroma subsample, and then does an 8x8 DCT.

The problem is, I have no idea if the images it's outputting are correct.

edit: Nevermind, figured it out, forgot to increment a variable!

Acer Pilot fucked around with this message at 12:09 on Jun 28, 2011

# ? Jun 28, 2011 07:39

qntm: Jun 17, 2009

Other than performance, are there any good reasons not to use exceptions for flow control?

# ? Jun 28, 2011 17:48

Internet Janitor: May 17, 2008; "That isn't the appropriate trash receptacle."

Exceptions have roughly the readability characteristics of a goto.

# ? Jun 28, 2011 18:04

Plorkyeran: Mar 22, 2007; To Escape The Shackles Of The Old Forums, We Must Reject The Tribal Negativity He Endorsed

Taken too far it's really easy to end up with incomprehensible spaghetti code that might as well be using goto for everything.

# ? Jun 28, 2011 18:06

Thermopyle: Jul 1, 2003; ...the stupid are cocksure while the intelligent are full of doubt. �Bertrand Russell

In Python, it's pretty common to use exceptions as flow control. Just pick what is the most readable and practical...

# ? Jun 28, 2011 18:24

qntm: Jun 17, 2009

The only reason goto is ever a problem is when it causes execution to jump backwards through a program. Exceptions are basically glorified breaks or returns, which I'm certain everybody loves.

# ? Jun 28, 2011 19:11

pokeyman: Nov 26, 2006; That elephant ate my entire platoon.

qntm posted:

Other than performance, are there any good reasons not to use exceptions for flow control?

Keep in mind what a reader of your code will likely expect. If an exception in the given language or domain typically means "terrible things happening", using them for flow control makes it harder for the reader to understand your code. If an exception is raised whenever an iterator completes, however, your reader may be used to seeing exceptions used this way.

# ? Jun 28, 2011 19:12

ultrafilter: Aug 23, 2007; It's okay if you have any questions.

pokeyman posted:

Keep in mind what a reader of your code will likely expect. If an exception in the given language or domain typically means "terrible things happening", using them for flow control makes it harder for the reader to understand your code. If an exception is raised whenever an iterator completes, however, your reader may be used to seeing exceptions used this way.

Exactly. It's not syntactically or semantically wrong to use exceptions for control flow, but it's pragmatically very bad.

# ? Jun 28, 2011 19:14

rolleyes: Nov 16, 2006; Sometimes you have to roll the hard... two?

All the C# guidance I've seen is along the lines of "Never use exceptions for flow control. No not even then. We mean it." and in a C# context I can't see any reason why you'd want to. Depends on the language I guess? But in most cases I've seen exceptions ruin readability when used in that way.

# ? Jun 28, 2011 19:16

baquerd: Jul 2, 2007; by FactsAreUseless

code:

    private class TrueResult extends Exception { };
    private class FalseResult extends Exception { };

    public void isOdd(Integer num) throws Exception {
        try {
            isNull(num);
        } catch (TrueResult t) {
            throw new IllegalArgumentException();
        } catch (FalseResult f) {
            if (num % 2 == 0) {
                throw new FalseResult();
            } else {
                throw new TrueResult();
            }
        }
    }
    
    public void isNull(Integer num) throws Exception {
        if (num == null) {
            throw new TrueResult();
        } else {
            throw new FalseResult();
        }
    }

# ? Jun 28, 2011 19:33

rolleyes: Nov 16, 2006; Sometimes you have to roll the hard... two?

Kill it with fire!

# ? Jun 28, 2011 19:38

Zombywuf: Mar 29, 2008

code:

struct number {};
struct integer : public number {
  int value;
};
struct floating : public number {
  float value;
};
void print(const number &x) {
  try {
    throw x;
  } catch (integer i) {
    print_int(i.value);
  } catch (floating f) {
    print_float(f.value);
  }
}

# ? Jun 29, 2011 08:36

qntm: Jun 17, 2009

Those are grotesque.

More, please.

# ? Jun 29, 2011 09:38

pseudorandom name: May 6, 2007

A good start, but perhaps it could be made into a more generalized solution with templates?

# ? Jun 29, 2011 18:17

rjmccall: Sep 7, 2007; no worries friend; Fun Shoe

Zombywuf posted:

code:

void print(const number &x) {
  try {
    throw x;

FWIW, this slices the object and will not be caught by either clause. Throwing a pointer wouldn't work either, because throws in C++ always use the static type of the exception expression.

# ? Jun 29, 2011 20:20

Pucklynn: Sep 8, 2010; chop chop chop

I'm learning to program as a hobby, and I spend seven hours a day parked in front of a computer at work. My work really doesn't require much, so I spend a lot of that time here on the forums. I don't have admin access to the computers, so I can't install Ruby or Python on them, so no matter how much time I spend reading about it, I can't get any actual programming practice during that time.

My question is, are there any ways I can practice programming over the internet? IE, set up a server on my home computer or something and upload files to it? I could just write stuff all day and test it when I get home, but I feel like I wouldn't really get there with that approach.

At the very least, is there a web-based version of IRB (interactive Ruby something something) where I could test my code?

# ? Jun 30, 2011 18:24

Thermopyle: Jul 1, 2003; ...the stupid are cocksure while the intelligent are full of doubt. �Bertrand Russell

Pucklynn posted:

I'm learning to program as a hobby, and I spend seven hours a day parked in front of a computer at work. My work really doesn't require much, so I spend a lot of that time here on the forums. I don't have admin access to the computers, so I can't install Ruby or Python on them, so no matter how much time I spend reading about it, I can't get any actual programming practice during that time.

My question is, are there any ways I can practice programming over the internet? IE, set up a server on my home computer or something and upload files to it? I could just write stuff all day and test it when I get home, but I feel like I wouldn't really get there with that approach.

At the very least, is there a web-based version of IRB (interactive Ruby something something) where I could test my code?

There's lots of online python interpreters. Just google "online python interpreter".

There's also Portable Python which doesn't require installation.

# ? Jun 30, 2011 18:28

mr_jim: Oct 30, 2006; OUT OF THE DARK

You could try http://codepad.org/, which has ruby and python interpreters. It's not quite the same as IRB, but it's pretty neat.

# ? Jun 30, 2011 18:29

Pucklynn: Sep 8, 2010; chop chop chop

CodePad just made me cackle and clap my hands together like an underage evil mastermind. Thank you!

# ? Jun 30, 2011 18:59

MutantBlue: Jun 8, 2001

Pucklynn posted:

CodePad just made me cackle and clap my hands together like an underage evil mastermind. Thank you!

Also look into Ideone, it's what I use for testing code snippets.

# ? Jun 30, 2011 21:48

Vulture Culture: Jul 14, 2003; I was never enjoying it. I only eat it for the nutrients.

Pucklynn posted:

My question is, are there any ways I can practice programming over the internet? IE, set up a server on my home computer or something and upload files to it? I could just write stuff all day and test it when I get home, but I feel like I wouldn't really get there with that approach.

At the very least, is there a web-based version of IRB (interactive Ruby something something) where I could test my code?

http://tryruby.org/

# ? Jun 30, 2011 23:58

ToxicFrog: Apr 26, 2008

Pucklynn posted:

I'm learning to program as a hobby, and I spend seven hours a day parked in front of a computer at work. My work really doesn't require much, so I spend a lot of that time here on the forums. I don't have admin access to the computers, so I can't install Ruby or Python on them, so no matter how much time I spend reading about it, I can't get any actual programming practice during that time.

My question is, are there any ways I can practice programming over the internet? IE, set up a server on my home computer or something and upload files to it? I could just write stuff all day and test it when I get home, but I feel like I wouldn't really get there with that approach.

At the very least, is there a web-based version of IRB (interactive Ruby something something) where I could test my code?

Others have already linked you to online interpreters. Other approaches you can use:

- Portable Cygwin does not require admin rights to run, and is a complete linuxy development environment, including python, ruby, lua, etc interpreters and C/C++ compilers. Requires some comfort with the command line.
- You can also set up a server at home and use a portable version of PuTTY or NXClient to talk to it from work, either simple uploading/downloading of files, or doing actual development remotely.

# ? Jul 1, 2011 00:30

Vulture Culture: Jul 14, 2003; I was never enjoying it. I only eat it for the nutrients.

DJ Bernstein's primegen utility contains this snippet in its source:

code:

void byte_copy(to,n,from)
register char *to;
register unsigned int n;
register char *from;
{
  for (;;) {
    if (!n) return; *to++ = *from++; --n;
    if (!n) return; *to++ = *from++; --n;
    if (!n) return; *to++ = *from++; --n;
    if (!n) return; *to++ = *from++; --n;
  }
}

Can anyone explain why the loop is doing... uh, whatever it is it's trying to accomplish by putting that same check four consecutive times?

# ? Jul 1, 2011 04:10

Blotto Skorzany: Nov 7, 2008; He's a PSoC, loose and runnin'
came the whisper from each lip
And he's here to do some business with
the bad ADC on his chip
bad ADC on his chiiiiip

Misogynist posted:

DJ Bernstein's primegen utility contains this snippet in its source:
code:
void byte_copy(to,n,from)
register char *to;
register unsigned int n;
register char *from;
{
  for (;;) {
    if (!n) return; *to++ = *from++; --n;
    if (!n) return; *to++ = *from++; --n;
    if (!n) return; *to++ = *from++; --n;
    if (!n) return; *to++ = *from++; --n;
  }
}
Can anyone explain why the loop is doing... uh, whatever it is it's trying to accomplish by putting that same check four consecutive times?

Unrolling the loop 4x manually

Between that, the fact that register is used (almost all compilers ignore it entirely), and pre-C89 function syntax is used, I'm tempted to think this is originally from something much older, but I wouldn't expect djb to do that given his nature, sooooooooo

Also the argument order is kinda curious imo

# ? Jul 1, 2011 04:15

Nippashish: Nov 2, 2005; Let me see you dance!

Misogynist posted:

Can anyone explain why the loop is doing... uh, whatever it is it's trying to accomplish by putting that same check four consecutive times?

It's been unrolled.

# ? Jul 1, 2011 04:15

Mustach: Mar 2, 2003; In this long line, there's been some real strange genes. You've got 'em all, with some extras thrown in.

Note that it's formatted in a confusing way for no good reason. This would've made it obvious that the if's aren't actually consecutive and that n is changing between each:

code:

void byte_copy(to,n,from)
register char *to;
register unsigned int n;
register char *from;
{
  for (;;) {
    if (!n) return;
    *to++ = *from++;
    --n;
    if (!n) return;
    *to++ = *from++;
    --n;
    if (!n) return;
    *to++ = *from++;
    --n;
    if (!n) return;
    *to++ = *from++;
    --n;
  }
}

# ? Jul 1, 2011 11:04

ChiralCondensate: Nov 13, 2007; what is that man doing to his colour palette?; Grimey Drawer

Mustach posted:

Note that it's formatted in a confusing way for no good reason.

Actually, there's a very good reason: having the same characters right on top of each other makes it easy at a glance to see that the four lines are exactly the same.

# ? Jul 1, 2011 14:12

Vulture Culture: Jul 14, 2003; I was never enjoying it. I only eat it for the nutrients.

Nippashish posted:

It's been unrolled.

I figured as much but was confused about why this would be done by hand instead of letting the compiler optimize it, then I realized that the compiler won't unroll an infinite loop for obvious reasons. Thanks.

# ? Jul 1, 2011 14:25

baquerd: Jul 2, 2007; by FactsAreUseless

Misogynist posted:

I figured as much but was confused about why this would be done by hand instead of letting the compiler optimize it, then I realized that the compiler won't unroll an infinite loop for obvious reasons. Thanks.

Even very modern compilers working with finite loops can benefit amazingly from manual loop unrolling, especially if you want to target specific hardware.

# ? Jul 1, 2011 15:34

MrMoo: Sep 14, 2000

The code is inefficient on current hardware though, you get better performance with by prefetching the source buffer in parallel and filling the cache line:

code:

void byte_copy(to,n,from)
register char *to;
register unsigned int n;
register char *from;
{
  int i = 0, count8 = n >> 3;
  if (count8) {
    while (count8--) {
      to[i]   = from[i];
      to[i+1] = from[i+1];
      to[i+2] = from[i+2];
      to[i+3] = from[i+3];
      to[i+4] = from[i+4];
      to[i+5] = from[i+5];
      to[i+6] = from[i+6];
      to[i+7] = from[i+7];
      i += 8;
    }
    n %= 8;
  }
  while (n--) {
    to[i] = from[i];
    i++;
  }
}

That's assuming the pointers are aligned, if they are not you can do a loop to align up first. If both pointers have different alignment you are screwed no matter what.

Similarly you can get more performance by copying with longer words but not always. Best performance is to use the assembler instruction for string copy if the string is long enough to overcome the instruction startup costs. On latest Nehalem chipsets as has been posted about a lot it's actually faster to copy in reverse than forward too.

MrMoo fucked around with this message at 16:10 on Jul 1, 2011

# ? Jul 1, 2011 16:04

Mustach: Mar 2, 2003; In this long line, there's been some real strange genes. You've got 'em all, with some extras thrown in.

ChiralCondensate posted:

Actually, there's a very good reason: having the same characters right on top of each other makes it easy at a glance to see that the four lines are exactly the same.

That sounds like a worthless reason to me.

# ? Jul 1, 2011 19:06

shrughes: Oct 11, 2008; (call/cc call/cc)

Mustach posted:

That sounds like a worthless reason to me.

You are a source code canonicalizationist and you will burn in hell.

# ? Jul 1, 2011 19:46

Vulture Culture: Jul 14, 2003; I was never enjoying it. I only eat it for the nutrients.

Are there any Haskell implementations that run from a USB key without too much screwing around?

# ? Jul 1, 2011 19:53

JetsGuy: Sep 17, 2003; science + hockey
=
LASER SKATES

EDIT: Wrong thread.

# ? Jul 1, 2011 22:06

Adbot: ADBOT LOVES YOU

# ? Jun 9, 2024 06:01

Mustach: Mar 2, 2003; In this long line, there's been some real strange genes. You've got 'em all, with some extras thrown in.

shrughes posted:

You are a source code canonicalization and you will burn in hell.

I just don't like seeing people miss return statements that are hidden within the same line as two other statements.

# ? Jul 1, 2011 22:56

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > Ask General Programming Questions Not Worth Their Own Thread

«‹›672 »