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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)?

#91

Post by sltkr »

oivey wrote: post #85
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…

Lots of the math in games and ML assumes you’re operating in the reals. For example, the optimization in neural networks. Integers and fixed point won’t work.

Doesn't ML work fine with fixed point numbers? I don't think there is a particular use case for very large or very small numbers.

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

#92

Post by salicideblock »

pfraze wrote: post #84
quelsolaar wrote: post #65

Earlier quoted context omitted.

As someone who has started out making games on Playstation 1 that didn't have floating point hardware, I can with authority say that developing games with only integers suck. Floating point number are far easier and robust to use.

Only integers? Wow. Were int pairs used to represent numbers with decimals or what?

In signal processing on constrained domains (constrained including the lack of an FPU), the usual alternative to floating point is "fixed point" arithmethic.

Basically you use the platform's native types (e.g. uint32) and decide which of the bits are for the integer part and which are for the fractional. uint32 can be interpreted as 20/12 for example. Your register went from representing "units" to representing "2^-12 increments of an unit". The ALU can do sum/comparison/subtractions transparently, but multiplications and (god forbid) divisions require shifting to return to the original representation.

The choice of how to split the bits is a tradeoff between range and precision. It can vary from one routine to another. It's a pain to compose code with it.

Short story: native float types are a blessing for programmer productivity and library interoperability.

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

#93

Post by taeric »

analog31 wrote: post #52
amelius wrote: post #36

Earlier quoted context omitted.

∞ is not a number. Using it as a number is a hack invented by mathematicians.

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...?

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

#94

Post by adwn »

bwestergard wrote: post #89
oivey wrote: post #85

Earlier quoted context omitted.

Lots of the math in games and ML assumes you’re operating in the reals. For example, the optimization in neural networks. Integers and fixed point won’t work.

Floats have a totally different algebra than the reals, though.

Only in the strictly mathematical sense. To a first approximation, floating-point numbers behave like real numbers, and that's good enough for many use-cases (not all, though).

Similarly, fixed-width integers have a totally different algebra than true integers, and yet they're immensely useful.

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

#95

Post by oivey »

bwestergard wrote: post #89
oivey wrote: post #85

Earlier quoted context omitted.

Lots of the math in games and ML assumes you’re operating in the reals. For example, the optimization in neural networks. Integers and fixed point won’t work.

Floats have a totally different algebra than the reals, though.

Yeah, but closer to the reals than fixed point or integers. That’s kind of the point of the standard.

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

#96

Post by TacticalCoder »

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 webserver basically busy-looping. Hence crashing the webserver in a few requests at most.

Now it'd be heresy if I were to say that maybe, just maybe, had the standards mandated to use 0 to 100 for weighting instead of 0 to 1.0 we could have dodged a whole source of potential issues!?

No, no, I realize this is heresy: let's all keep using numbers that cannot even be represented correctly (except as strings), parse those strings into something approximately representing what's written in the string, then make more approximation errors while doing computation with these numbers, propagation errors, epsilon estimation errors, and keep insisting we all could have authored "What every computer scientist should known about floating-point numbers" (which is 80 pages long and, well, approaching a treaty) ; )

/rant off

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

#97

Post by linkdd »

pfraze wrote: post #84
quelsolaar wrote: post #65

Earlier quoted context omitted.

As someone who has started out making games on Playstation 1 that didn't have floating point hardware, I can with authority say that developing games with only integers suck. Floating point number are far easier and robust to use.

Only integers? Wow. Were int pairs used to represent numbers with decimals or what?

Let's say you have two 4 bits integer to form an 8 bit decimal number:

1111.1111 is (1 + 2 + 4 + 8) + (1/2 + 1/4 + 1/8 + 1/16)

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

#98

Post by rav »

brandmeyer wrote: post #54
marcosdumay wrote: post #31

Earlier quoted context omitted.

You shouldn't really use equality on floating point numbers, except on very special circumstances (and I imagine the == behavior for 0 breaks things more often than it helps). But the wikipedia page on -0 has your case covered: > According to the IEEE 754 standard, negative zero and positive zero should compare as equal with the usual (numerical) comparison operators, like the == operators of C and Java. In those lan…

> You shouldn't really use equality on floating point numbers, except on very special circumstances. This is very common advice, so common that it gets cargo-culted into situations where it is really quite poor. Information storage, retrieval, and transmission systems should faithfully deliver floating-point values that are good to the last bit. Round-trips through databases, transmission over network protocols, etc…

By "the last bit" do you mean the 32nd bit or the 64th bit? :-)

Many times I've tracked down the place in our stack where a double-precision value from user input accidentally goes through a single-precision variable in some C code somewhere and crashes some Python code later on because the values don't match "to the last bit" in the way that the programmer thought... But that's a bug in the C code - I agree completely the the system SHOULD give the value back that was put into it!

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

#99

Post by adwn »

linkdd wrote: post #83
quelsolaar wrote: post #78

Earlier quoted context omitted.

>And computing integers IS faster than computing floats, at least on a CPU. In the abstract yes. In reality not so much. A lot of what floats are used for in games is vector math (you are often in a 2D/3D world), and vector math in fixed point requires a lot more work in integer math since you constantly need to shift down things in order to avoid overflow. Overflow bugs are a constant problem when doing dot products…

I never use the square root in games, I always compare squared distances (since the properties are the same). If you try to do with Fixed Point Arithmetic what was intended to be done with Floating Point, you're the problem. A 32 bits integer can hold values up to 4 billions, if I have that kind of value in a simple game, then yes i will switch to Floating Point Arithmetic, but when does that use case happen if you'r…

It appears you have a very niche definition of "game", one which excludes basically all 3D games.

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

#100

Post by scrooched_moose »

quelsolaar wrote: post #65
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…

As someone who has started out making games on Playstation 1 that didn't have floating point hardware, I can with authority say that developing games with only integers suck. Floating point number are far easier and robust to use.

Isn't that what caused the PS1 graphics "wobble"? I remember you could just stare at a wall, rotate the camera, and the textures would slightly jitter and move. It's really obvious in some the Metal Gear cutscenes, especially this conversation with Donald Anderson where the camera pans up from the floor (at 15m) or the sweep(15m31s):

https://www.youtube.com/watch?v=VLTqIXZ1jQQ#t=15m00s

I never had a PS1 but it always bugged me when playing on someone elses.

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