Weird Code

141

Author

July 02, 2012 07:41 PM

I found this odd peice of code on cplusplus.com



bool integer::resize(VERY long ns)

{

	if (ns == size)

		return true && false;

	if (ns == 0)

		{

			NUL = true;

			//delete [] number;

			return true || false;

		}

	if (ns > size && ns <= memory)

		return size = ns, false, true;

	if (ns > memory)

		{

			integer copy (*this);

			delete [] number;

			size = ns;

			memory = (size%mem_chunk_size == 0) ? size/mem_chunk_size:(size/mem_chunk_size+1)*mem_chunk_size;

			number = new digit[memory];

			initialize();

			for (VERY BIG NUMBER i = memory - size; i < memory; ++i)

				number = copy.number;

			return size == ns;

		}

	if (ns < size && memory == (memory = (ns < mem_chunk_size) ? mem_chunk_size: ns%mem_chunk_size == 0 ? ns/mem_chunk_size*mem_chunk_size:(ns/mem_chunk_size+1)*mem_chunk_size), memory)

		{

			integer copy(*this);

			delete [] number;

			size = ns;

			number = new digit[memory],

			initialize();

			bool rv = true;

			for (VERY BIG NUMBER i = memory - size, j = copy.memory-size; i < memory, j < memory; ++i, ++j)

				//number = number[j];

				if ( number = number[j] );

			else rv = false;

			return true || false, ns == size && memory == memory && rv;

		}

}

What does it mean? It doesnt really make sense to me.

How can you return true and false?

ApochPiQ

23,138

July 02, 2012 07:47 PM

That code is utter crap, in numerous ways, but that's kind of irrelevant to your question :-)

To explain how the returns work: remember that everything to the right of the "return" keyword is evaluated as a standalone expression, and the result of that evaluation is what is actually returned. So the expression "true && false" is going to evaluate to false, so that could be simplified to "return false". On the flip side, "true || false" is going to be true always, so that's just "return true".

Then there's the horrible, awful, evil abuse of the comma operator. Frankly I hate the comma operator and refuse to remember its semantics, so I can't tell you off the top of my head what that does because I don't want to think about it ;-) But you can probably figure it out by remembering the above rule of thumb.

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boogyman19946

1,487

July 02, 2012 08:15 PM

I've never heard of the comma operator before, but having looked it up, that whole statement doesn't make any sense to me.

I just tested a statement similar to the one above and it seems that the operator will always return the second operand, so the first operand doesn't seem to have an effect. Is the true || false statement completely useless then?

Yo dawg, don't even trip.

frob

46,222

July 02, 2012 08:22 PM

I've never heard of the comma operator before, but having looked it up, that whole statement doesn't make any sense to me.

I just tested a statement similar to the one above and it seems that the operator will always return the second operand, so the first operand doesn't seem to have an effect. Is the true || false statement completely useless then?

It will run, effectively do nothing, and the result will be discarded. The optimizer will probably remove it.

I've got to agree that the code is garbage, written to confuse and mislead rather than to convey the meaning behind the code.

As for its intent, it appears to be part of a "large integer" class, that holds very large integers. It appears to resize a portion of the memory needed to hold that very large number, expanding or contracting as necessary. It does so with quite a lot of unnecessary complexity.

Narf the Mouse

322

July 02, 2012 09:03 PM

It also means someone in the company may be a Wally.

(If you don't recognize the reference, read Dilbert)

Now open: MouseProduced Games

Alex Melbourne

294

July 05, 2012 06:07 PM

I've never heard of the comma operator before, but having looked it up, that whole statement doesn't make any sense to me.

The comma operator should not be confused with the comma that appears in function calls or declaration lists. Ever. They are not the same thing.

Now that that is cleared up: the comma operator is a method of chaining statements together. It is left-to-right associative and thus will return the latter of the two operands (the one on the right). Unlike other operators in C and C++ the comma operator guarantees that it's operands will be evaluated in order; this means that effects from the first operation (although the result is discarded) will be available to the second.

boogyman19946

1,487

July 05, 2012 06:45 PM

[quote name='boogyman19946' timestamp='1341260113' post='4955026']I've never heard of the comma operator before, but having looked it up, that whole statement doesn't make any sense to me.

The comma operator should not be confused with the comma that appears in function calls or declaration lists. Ever. They are not the same thing.

Now that that is cleared up: the comma operator is a method of chaining statements together. It is left-to-right associative and thus will return the latter of the two operands (the one on the right). Unlike other operators in C and C++ the comma operator guarantees that it's operands will be evaluated in order; this means that effects from the first operation (although the result is discarded) will be available to the second.
[/quote]

I know that, which is exactly why the statement does not make any sense.

The statement

[color=#000088]return[color=#000000] [color=#000088]true[color=#000000] [color=#666600]||[color=#000000] [color=#000088]false[color=#666600],[color=#000000] ns [color=#666600]==[color=#000000] size [color=#666600]&&[color=#000000] memory [color=#666600]==[color=#000000] memory [color=#666600]&&[color=#000000] rv[color=#666600];

is, as far as I can see, exactly the same as if the comma operator was not used there at all. It's not the operator that's confusing me, it's the seemingly useless application of it.

Yo dawg, don't even trip.

Alex Melbourne

294

July 05, 2012 06:50 PM

I know that, which is exactly why the statement does not make any sense.

The statement

return true || false, ns == size && memory == memory && rv;

is, as far as I can see, exactly the same as if the comma operator was not used there at all. It's not the operator that's confusing me, it's the seemingly useless application of it.

Oh, my apologise. Yeah, the logical operators only evaluate their second operand if the condition isn't satisfied by the first (if the first is false in an 'or' expression, or if the first is true in an 'and' expression) so you're completely right - the rest of the expression is completely pointless.

The whole example is really, really shoddy and probably shouldn't be analysed for how it behaves. It should be framed so that no-one ever writes such awful shit ever again and the author should be burnt at the stake.

NightCreature83

5,061

July 05, 2012 10:04 PM

This is code that is constructed for a code obfuscation contest I think, this line kinda points it out



if (ns < size && memory == (memory = (ns < mem_chunk_size) ? mem_chunk_size: ns%mem_chunk_size == 0 ? ns/mem_chunk_size*mem_chunk_size:(ns/mem_chunk_size+1)*mem_chunk_size), memory)

So many side effects, I like how the comma operator in the end is used to check whether the memory variable isn't zero lol.

For reference this is the article on cplusplus.com: http://www.cplusplus...beginner/49612/

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