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Re: 0.30000000000000004

#61

Post by tomca32 »

jonny_eh wrote: post #36

> It's actually pretty simple The explanation then goes on to be very complex. e.g. "it can only express fractions that use a prime factor of the base". Please don't say things like this when explaining things to people, it makes them feel stupid if it doesn't click with the first explanation. I suggest instead "It's actually rather interesting".

The problem is that almost everything is simple once you understand it. Once you understand something, you think it's pretty simple to explain it.

On the other hand, people say "it's actually pretty simple" to encourage someone to listen to the explanation rather than to give up before they even heard anything, as we often do.

Re: 0.30000000000000004

#63

Post by pmarreck »

IEEE floating-point is disgusting. The non-determinism and illusion of accuracy is just wrong.

I use integer or fixed-point decimal if at all possible. If the algorithm needs floats, I convert it to work with integer or fixed-point decimal instead. (Or if possible, I see the decimal point as a "rendering concern" and just do the math in integers and leave the view to put the decimal by whatever my selected precision is.)

Re: 0.30000000000000004

#64

Post by hyperpape »

jonny_eh wrote: post #36

> It's actually pretty simple The explanation then goes on to be very complex. e.g. "it can only express fractions that use a prime factor of the base". Please don't say things like this when explaining things to people, it makes them feel stupid if it doesn't click with the first explanation. I suggest instead "It's actually rather interesting".

I rather like http://fabiensanglard.net/floating_point_visually_explained/

Re: 0.30000000000000004

#65

Post by ChuckMcM »

That is why I only used base 2310 for my floating point numbers :-). FWIW there are some really interesting decimal format floating point libraries out there (see http://speleotrove.com/decimal/ and https://github.com/MARTIMM/Decimal) and the early computers had decimal as a native type (https://en.wikipedia.org/wiki/Decimal_computer#Early_compute...)

Re: 0.30000000000000004

#66

Post by _bxg1 »

munchbunny wrote: post #52
_bxg1 wrote: post #40

Earlier quoted context omitted.

I actually ran into a bug recently while implementing my first raytracer, where the point calculated from the sphere-intersect test would just occasionally end up inside the sphere due to floating point imprecision, so the diffuse sample rays would have their origins completely in the dark, leading to randomly black pixels. Solved it by bumping every intersection out by 0.01 in the direction of its normal. And then o…

That's really interesting - hadn't thought of that before. To fix that, would you be able to do a square of the magnitude comparison with the radius and just bump the borderline cases, or is it more efficient without the extra branching?

I just did it across the board; since the error is in the floating-point noise I don't know if I'd even trust a comparison on that. Plus, the discrepancy between "bumped" and "unbumped" samples might cause some visible artifacts.

Re: 0.30000000000000004

#67

Post by _y5hn »

_bxg1 wrote: post #17

I remember in college when we learned about this and I had the thought, "Why don't we just store the numerator and denominator?", and threw together a little C++ class complete with (then novel, to me) operator-overloads, which implemented the concept. I felt very proud of myself. Then years later I learned that it's a thing people actually use: https://en.wikipedia.org/wiki/Rational_data_type

It's actually in use in many places, for things like handling currency and money, and for when you get funny corner cases involving rounding such numbers and pooling the change.

Whenever I see someone handling currency in floats, something inside me wither and die a small death.

Re: 0.30000000000000004

#68

Post by snickerbockers »

amelius wrote: post #55
snickerbockers wrote: post #49

Earlier quoted context omitted.

That's not a floating point.

From the article: > Programmable calculators manufactured by Texas Instruments, Hewlett-Packard, and others typically employ a floating-point BCD format, typically with two or three digits for the (decimal) exponent.

Then that's how they're encoding the components of the float. BCD itself is not a floating-point, it's just a different way of encoding a fixed-point or integer. If all you want to do is use floating point but expand the logarithm and mantissa then that's completely tangential to whether or not they're stored as BCD or regular binary values.

Re: 0.30000000000000004

#69

Post by ggggtez »

jonny_eh wrote: post #36

> It's actually pretty simple The explanation then goes on to be very complex. e.g. "it can only express fractions that use a prime factor of the base". Please don't say things like this when explaining things to people, it makes them feel stupid if it doesn't click with the first explanation. I suggest instead "It's actually rather interesting".

>Why does this happen? It's actually rather interesting.

Did the text change in the last 15 minutes?

Re: 0.30000000000000004

#70

Post by Dylan16807 »

tomca32 wrote: post #61
jonny_eh wrote: post #36

> It's actually pretty simple The explanation then goes on to be very complex. e.g. "it can only express fractions that use a prime factor of the base". Please don't say things like this when explaining things to people, it makes them feel stupid if it doesn't click with the first explanation. I suggest instead "It's actually rather interesting".

The problem is that almost everything is simple once you understand it. Once you understand something, you think it's pretty simple to explain it. On the other hand, people say "it's actually pretty simple" to encourage someone to listen to the explanation rather than to give up before they even heard anything, as we often do.

I understand prime factors just fine, but I'd never think it's "simple" to bring them up when I'm explaining how decimal points work.
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