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Cryptic genetic variation in software: hunting a buffered 41-year-old bug

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Re: Cryptic genetic variation in software: hunting a buffered 41-year-old bug

#21

Post by [deleted] »

cgio wrote: post #18
entropy_ wrote: post #13

Earlier quoted context omitted.

I learned Math in a french-system school and yes, that's definitely a much better notation in my opinion. The difference between [] and () is not immediately clear, whereas [a,b] versus ]a,b[ makes it obvious that one includes a and b while the other does not. It also makes it easy to remember "open" and "closed" and what they mean in terms of whether or not the interval bounds are included or excluded

I don't know if it's very intuitive given that a and be are still inside the ][. Maybe a]..[b would make it clearer?

[deleted]

Re: Cryptic genetic variation in software: hunting a buffered 41-year-old bug

#22

Post by mlvljr »

cgio wrote: post #18
entropy_ wrote: post #13

Earlier quoted context omitted.

I learned Math in a french-system school and yes, that's definitely a much better notation in my opinion. The difference between [] and () is not immediately clear, whereas [a,b] versus ]a,b[ makes it obvious that one includes a and b while the other does not. It also makes it easy to remember "open" and "closed" and what they mean in terms of whether or not the interval bounds are included or excluded

I don't know if it's very intuitive given that a and be are still inside the ][. Maybe a]..[b would make it clearer?

just a][b :)

Re: Cryptic genetic variation in software: hunting a buffered 41-year-old bug

#23

Post by ntlve »

jdpage wrote: post #19
matthewcanty wrote: post #4

That was a really interesting read, and very well written. I wonder if anyone can clear this up though... I find the terminology of open and closed intervals contradictory to their meaning. Does anyone know why they are described like this? `Closed` makes me think shut or not-including - however it includes its endpoints. `Open` makes me think inclusive - yet does not include its endpoints.

From a real analysis standpoint... the definition of a 'closed set' in an N-dimensional metric space (of which Euclidean space, i.e. normal space, is an example) is as follows: a set C is 'closed' if and only if, given any sequence of elements (x_n) converging on x, such that (x_n) is a subset of C, it follows that x is also in C. Under this definition, 'closed' makes sense in the larger context, since in mathematics…

Out of curiosity, do you have any examples or references to something with examples of sets that are neither open nor closed?

Re: Cryptic genetic variation in software: hunting a buffered 41-year-old bug

#25

Post by mnembrini »

ntlve wrote: post #23
jdpage wrote: post #19

Earlier quoted context omitted.

From a real analysis standpoint... the definition of a 'closed set' in an N-dimensional metric space (of which Euclidean space, i.e. normal space, is an example) is as follows: a set C is 'closed' if and only if, given any sequence of elements (x_n) converging on x, such that (x_n) is a subset of C, it follows that x is also in C. Under this definition, 'closed' makes sense in the larger context, since in mathematics…

Out of curiosity, do you have any examples or references to something with examples of sets that are neither open nor closed?

[0,1) = {x | 0<=x<1} is probably the simplest example.

Re: Cryptic genetic variation in software: hunting a buffered 41-year-old bug

#26

Post by anon4 »

matthewcanty wrote: post #4

That was a really interesting read, and very well written. I wonder if anyone can clear this up though... I find the terminology of open and closed intervals contradictory to their meaning. Does anyone know why they are described like this? `Closed` makes me think shut or not-including - however it includes its endpoints. `Open` makes me think inclusive - yet does not include its endpoints.

Think of Tom&Jerry. Open is when Tom is running on a carpet towards an open door, but the carpet is moving under him and he never reaches the door. Closed is when Tom slams into a closed door and gets flattened.

Re: Cryptic genetic variation in software: hunting a buffered 41-year-old bug

#29

Post by PhantomGremlin »

At least one, possibly two other bugs lurking in the implementation.

1) Algorithm FT says:

    1. Generate u. Store the first bit of u
    as a sign s (s=0 if u=1/2).
and yet the C code implements

    if ( u
2) I can't be sure of the following w/o access to doc. But i4_uni() says

    a uniform distribution over (1, 2147483562)
which, offhand, is suspicious. A distribution over positive integers would probably want to use all available values in a 32-bit signed int, so it would most likely end at 2^31 -1 which is 2147483647, and not the value given.

Re: Cryptic genetic variation in software: hunting a buffered 41-year-old bug

#30

Post by GFK_of_xmaspast »

jdpage wrote: post #19
matthewcanty wrote: post #4

That was a really interesting read, and very well written. I wonder if anyone can clear this up though... I find the terminology of open and closed intervals contradictory to their meaning. Does anyone know why they are described like this? `Closed` makes me think shut or not-including - however it includes its endpoints. `Open` makes me think inclusive - yet does not include its endpoints.

From a real analysis standpoint... the definition of a 'closed set' in an N-dimensional metric space (of which Euclidean space, i.e. normal space, is an example) is as follows: a set C is 'closed' if and only if, given any sequence of elements (x_n) converging on x, such that (x_n) is a subset of C, it follows that x is also in C. Under this definition, 'closed' makes sense in the larger context, since in mathematics…

You can also have sets that are simultaneously closed and open.
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