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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)?

#131

Post by bjourne »

taeric wrote: post #93
analog31 wrote: post #52

Earlier quoted context omitted.

That's right. It's a symbol. When you see it in an expression, you're probably expected to interpret it in light of a limit of some kind. It's just convenient to write it into an expression rather than use cumbersome limit notation all over the place. Like many notational shortcuts, it's a hack supported by proof. ;-)

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

Yes, in a way. What distinguishes irrational numbers from rational numbers is that all rational numbers can be represented by strings drawn from a regular language. For example, all strings generated by the regular language "-?\d+\.\d+?_\d+" (where "_" denotes the repeating decimal expansion as in 1/6 = 0.1_6) correspond to exactly one rational number and all rational numbers correspond to at least one string in this regular language. Irrational numbers (and other types of "numbers" such as +inf and -inf) cannot be represented by any such regular language.

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

#132

Post by mattgreenrocks »

strictfp wrote: post #122
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…

Meh, it's not like there can't be a bug in whatever other parsing code a webserver uses. Maybe using a float is overkill in this case, since you're never going to hit more than a hundred languages. But it's at least not setting any limitations.

The issue is that the representation of floating point numbers imposes additional cognitive burden that the code must handle. How does the web server header parsing code handle positive/negative infinity? How about NaN?

NaNs/infs are particularly vicious, as they propagate through computations.

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

#133

Post by civilized »

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…

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 for them. But there's a lot more to computing than business software.

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

#134

Post by kevin_thibedeau »

TacticalCoder wrote: post #96
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…

> 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.

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

#135

Post by mattgreenrocks »

magicalhippo wrote: post #76

I recall there being an issue with double.GetHashCode() in the early versions of .Net, where it would return different hash values for 0.0 and -0.0. That got fixed, but it seems a variation with signed NaN recently got fixed[1] in .Net Core (taking care to handle all the possible NaN values). Floats are deceptively easy to use. Which is nice but kinda sucks too, given all the footguns they bring to the party. [1]: ht…

The fact that NaN is technically a set of values in IEEE-754 (rather than just one agreed-upon value) was quite eye-opening to me.

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

#136

Post by neurocline »

quelsolaar wrote: post #66
linkdd wrote: post #64

Earlier quoted context omitted.

In some game engines, Fixed Point Arithmetic is used instead of Floating Point, because it's faster, and the approximation is generally good enough for a game.

I dont think this is true. Integer math is used in some game engines because they need to be deterministic, between networked computers (and different CPUs rounds floating point numbers differently). I have written an engine like that, and i know that Starcraft 2 is all integer for the same reason. No one does it because its faster or easier. Its a pain.

Starcraft II uses floats, but for the game simulation portion it uses an internal software floating-point library to ensure consistency.

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

#137

Post by amelius »

civilized wrote: post #133
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…

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.

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

#138

Post by lostcolony »

strictfp wrote: post #122
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…

Meh, it's not like there can't be a bug in whatever other parsing code a webserver uses. Maybe using a float is overkill in this case, since you're never going to hit more than a hundred languages. But it's at least not setting any limitations.

Based on the OP, this was the official parser for floats. That's a bit more extravagant of a bug.

I also would invite you to find a similar instance where a parsing bug for integers crashes the server. Not throws an exception, but falls over in an uncatchable way. I'm not sure I have ever seen one.

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

#139

Post by duckerude »

strictfp wrote: post #122
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…

Meh, it's not like there can't be a bug in whatever other parsing code a webserver uses. Maybe using a float is overkill in this case, since you're never going to hit more than a hundred languages. But it's at least not setting any limitations.

No, it is setting limitations, they're just harder to understand and predict. Here's what the RFC says:

  qvalue         = ( "0" [ "." 0*3DIGIT ] )
                 | ( "1" [ "." 0*3("0") ] )
(https://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3....)

There are 1001 valid values with 1117 representations. Only in practice, Firefox clamps to 2 decimal places, and it used to clamp to 1 decimal place (https://bugzilla.mozilla.org/show_bug.cgi?id=672448), and who knows what other software does.

And it gets worse: the grandparent suggests there are servers that parse it as floating point. Do they accept q=1e2? If they accept it, are there clients that send it? Do you need to be compatible with those clients?

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

#140

Post by taeric »

bjourne wrote: post #131
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...?

Yes, in a way. What distinguishes irrational numbers from rational numbers is that all rational numbers can be represented by strings drawn from a regular language. For example, all strings generated by the regular language "-?\d+\.\d+?_\d+" (where "_" denotes the repeating decimal expansion as in 1/6 = 0.1_6) correspond to exactly one rational number and all rational numbers correspond to at least one string in this…

I'm not entirely sure I follow. Aren't pi and e irrational numbers?

I also included .9_ as it is an easy trap to show we have two ways of writing 1 in standard decimal notation.

Please read this whole post as a question. I'm genuinely not clear on the distinction.

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