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How does your programming language handle “minus zero” (-0.0)?

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Re: How does your programming language handle “minus zero” (-0.0)?

#141

Post by lostcolony »

amelius wrote: post #137
civilized wrote: post #133

Earlier quoted context omitted.

Floats are essential for machine learning, scientific computing, and any other application where the goal is to model mathematical processes involving real numbers. The idea that there is something out there that could do the job better than floats is almost certainly wrong. I'm fascinated by how common it is for programmers to hate floats. Yes, if you write business software for a living you may not have much use fo…

> Floats are essential for Not necessarily true. Theoretically you can replace floats by fixed-point representations given enough bits, and in practice this also works often. It's a pity languages/hardware don't have good built-in support for fixed-point numbers though.

Well, as mentioned elsewhere, because of historical purposes, GPUs tend to optimize floating point operations really heavily. Whereas bigint style things likely don't benefit, in part because there's no "standard" for them at that low a level. So it seems to me to be a bit of chicken and egg; low level languages don't have them as part of the standard, so graphic cards can't universally optimize for them, and since graphic cards don't support optimizations for them, there isn't anyone clamoring for it.

Re: How does your programming language handle “minus zero” (-0.0)?

#142

Post by taeric »

gefh wrote: post #129
taeric wrote: post #93

Earlier quoted context omitted.

This explanation feels off, to me. Aren't all numbers symbols? Pi, e, 10, 0xA, 9.99999...?

But not all symbols are numbers.

Why not? One of the profound effects of computers is that we have moved computing to be able to work with images. Sounds. Etc.

I get that not all have simple algebraic concepts.

I get the impression I'm corrupting parts of I am a Strange Loop? Would love to read more on this.

Re: How does your programming language handle “minus zero” (-0.0)?

#143

Post by BeetleB »

chrisseaton wrote: post #7
bendiksolheim wrote: post #2

Does anyone have a good example of a programming problem where we _need_ signed zero? Or where it makes things significantly simpler? As far as I know, there is no distinction between -0 and +0 in math, so I have never really understood why this is a thing in computers.

Computers (obviously) have to approximate the majority of actual mathematical numbers, as they do not have infinite storage. If you've got two numbers, +0.0000001 and -0.0000001, but you can't represent that precision, can you see how it's less bad to round to +0.0000 and -0.0000 rather than to just 0.0000? It's encoding strictly more information.

One should usually not rely on this, unless your language gives guarantees. I don't think even IEEE 754 gives you the guarantee you are implying.

To give you an idea, the C99 standard does not require signed zeros, and if you have them, does not dictate the behavior you are describing. I once worked on a commercial C compiler and we produced a new version that resulted in a change of sign of zero for the exact same computation (and even "worse", would give a different sign on different machines for the same compiler version). We discussed this thoroughly and decided it was OK because our docs made it clear we conform to C99 (which provides no guarantees on signed zero).

Re: How does your programming language handle “minus zero” (-0.0)?

#145

Post by taeric »

analog31 wrote: post #126
taeric wrote: post #93

Earlier quoted context omitted.

This explanation feels off, to me. Aren't all numbers symbols? Pi, e, 10, 0xA, 9.99999...?

In my view, numbers are numbers, and symbols are symbols. There's an agreement that a symbol represents a number, but there's not a one-to-one relationship between available symbols and available numbers. Normally this isn't a problem, and we treat them interchangeably. And indeed the distinction may only be a philosophical oddity or a matter for mathematicians. But I believe nonetheless that there is a distinction.…

I think the consequences of what you are saying makes sense. Would be neat to explore more of the idea. I was starting to find, recently, that it was better to think of numbers as symbols that follow operational rules. This view seems counter to that.

Re: How does your programming language handle “minus zero” (-0.0)?

#146

Post by BeetleB »

chrisseaton wrote: post #21
numlock86 wrote: post #12

Earlier quoted context omitted.

Ok, so what's true? -0<+0 or -0==+0

You can look these things up for yourself - they're standardised in most language's implementations in something called IEEE 754. In the cases you've asked about they're false and true. Is this what you want in all cases? No. Is this what you want in some cases? Yes. It's a tradeoff. You can still observe the difference by dividing by zero (which should be another indication that these aren't real numbers as we're co…

> they're standardised in most language's implementations in something called IEEE 754

There is the IEEE 754, and there is the language's standard. One should always look at the latter because it's often the case that the language doesn't fully conform to IEEE 754.

Re: How does your programming language handle “minus zero” (-0.0)?

#147

Post by analog31 »

taeric wrote: post #145
analog31 wrote: post #126

Earlier quoted context omitted.

In my view, numbers are numbers, and symbols are symbols. There's an agreement that a symbol represents a number, but there's not a one-to-one relationship between available symbols and available numbers. Normally this isn't a problem, and we treat them interchangeably. And indeed the distinction may only be a philosophical oddity or a matter for mathematicians. But I believe nonetheless that there is a distinction.…

I think the consequences of what you are saying makes sense. Would be neat to explore more of the idea. I was starting to find, recently, that it was better to think of numbers as symbols that follow operational rules. This view seems counter to that.

There is a view that math is "just" symbol manipulation. So I can't say your approach is wrong. Probably whatever works, works.

And you can usefully say things like "x is a number" without saying which particular number x is.

Re: How does your programming language handle “minus zero” (-0.0)?

#148

Post by toast0 »

kevin_thibedeau wrote: post #134
TacticalCoder wrote: post #96

Earlier quoted context omitted.

> When they do it's often a mistake, like for currency. The most beautiful FP bug I remember was a denial of service in some webservers where by setting the header "Accepted Language: en-gb;q=0.3 en;q=0.8 ..." to a specific value you could send the official Java floating-point parser in an infinite loop (and this affected several Java webservers). So at each webpage request, you were sending one CPU core of the webse…

Don't blame the protocol, blame the language. Nothing prevents the use of fixed point for such numbers. It's just the Java ecosystem and the weakness of languages that use pervasive exceptions to the point that nobody can keep track of them all that is the cause of such issues.

> Don't blame the protocol, blame the language. Nothing prevents the use of fixed point for such numbers.

I absolutely blame the protocol. Fixed point isn't widely available and used, but integers are. Someone below says protocol spec goes to three digits past the decimal. Using a constrained integer would have allowed the same range of values, but without the complexity of decimal numbers; that's a protocol mistake.

In addition to the ease of using floating point numbers to incorrectly represent decimals, there's also fun with formatting, comma vs period, number of digits to report, etc.

Re: How does your programming language handle “minus zero” (-0.0)?

#149

Post by bjourne »

chrisseaton wrote: post #7
bendiksolheim wrote: post #2

Does anyone have a good example of a programming problem where we _need_ signed zero? Or where it makes things significantly simpler? As far as I know, there is no distinction between -0 and +0 in math, so I have never really understood why this is a thing in computers.

Computers (obviously) have to approximate the majority of actual mathematical numbers, as they do not have infinite storage. If you've got two numbers, +0.0000001 and -0.0000001, but you can't represent that precision, can you see how it's less bad to round to +0.0000 and -0.0000 rather than to just 0.0000? It's encoding strictly more information.

More information isn't better if that information isn't useful. Does x*0 evaluate to 0.0? Not with -0 around. Does x+0 evaluate to x? Maybe!

Re: How does your programming language handle “minus zero” (-0.0)?

#150

Post by emiliobumachar »

TorKlingberg wrote: post #60

I feel like floating point is a completely separate branch of programming that a lot of coders never use. When they do it's often a mistake, like for currency. Yet floating point is very useful for scientific calculations and simulations, which is what computers were all about for the first couple of decades. I have a suspicion that on a fundamental level, floating point isn't actually good for games or machine learn…

> very useful for scientific calculations and simulations

Don't forget control systems.

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