@programminginc - страница 2041

Artöm

Write it yourself

klimi

give me the source code

Ha ha

rex

i cant use strrev function because it is not defined in gcc compiler

rex

and again if i reversing the string character wise just tell me logic

Artöm

Use for, swap i and (last-i) chars, i from 0 to (length/2)

Artöm

C or C++?

Artöm

i cant use strrev function because it is not defined in gcc compiler

You may try adding -D_GNU_SOURCE to compiler invocation

Pavel

I want to implement a simple float comparison with epsilon in my project. But I also want to check with assertions that the values have comparable magnitudes with the given epsilon (so no one tries to compare one billion with something else using epsilon of 0.0001f). Is there a way to achieve that? bool AreFloatsComparable(float a, float b, float epsilon) { return ??? } bool AreEqualWithEpsilon(float a, float b, float epsilon) { Assert(AreFloatsComparable(a, b, epsilon), "error: ..."); return fabs(a - b) < epsilon; }

Mar!o

I want to implement a simple float comparison with epsilon in my project. But I also want to check with assertions that the values have comparable magnitudes with the given epsilon (so no one tries to compare one billion with something else using epsilon of 0.0001f). Is there a way to achieve that? bool AreFloatsComparable(float a, float b, float epsilon) { return ??? } bool AreEqualWithEpsilon(float a, float b, float epsilon) { Assert(AreFloatsComparable(a, b, epsilon), "error: ..."); return fabs(a - b) < epsilon; }

I have some code for that Ill send it when Im home

Mar!o

[[nodiscard]] inline NO_ALIAS auto is_zero(const f32 v) noexcept->bool { return abs(v) < 1e-6f; } [[nodiscard]] inline NO_ALIAS auto is_one(const f32 v) noexcept->bool { return is_zero(v - 1.f); } [[nodiscard]] inline NO_ALIAS auto near_equal(const f32 a, const f32 b) noexcept->bool { if (is_zero(a - b)) return true; const s32 a2 = *reinterpret_cast<const s32*>(&a); const s32 b2 = *reinterpret_cast<const s32*>(&a); if (a2 < 0 != b2 < 0) return false; return abs(a2 - b2) <= 0b0100; } [[nodiscard]] constexpr NO_ALIAS auto within_epsilon(const f32 a, const f32 b, const f32 epsilon) noexcept->bool { const f32 num = a - b; return -epsilon <= num && num <= epsilon; }

Mar!o

Here just replace f32 with float and s32 with int, NO_ALIAS with __declspec(noalias) (only if you are on windows, otherwise remove it).

Giri

[[nodiscard]] inline NO_ALIAS auto is_zero(const f32 v) noexcept->bool { return abs(v) < 1e-6f; } [[nodiscard]] inline NO_ALIAS auto is_one(const f32 v) noexcept->bool { return is_zero(v - 1.f); } [[nodiscard]] inline NO_ALIAS auto near_equal(const f32 a, const f32 b) noexcept->bool { if (is_zero(a - b)) return true; const s32 a2 = *reinterpret_cast<const s32*>(&a); const s32 b2 = *reinterpret_cast<const s32*>(&a); if (a2 < 0 != b2 < 0) return false; return abs(a2 - b2) <= 0b0100; } [[nodiscard]] constexpr NO_ALIAS auto within_epsilon(const f32 a, const f32 b, const f32 epsilon) noexcept->bool { const f32 num = a - b; return -epsilon <= num && num <= epsilon; }

What abt this 🤯

Mar!o

This is code for correctly comparing floating point numbers using epsilons :)

Pavel

[[nodiscard]] inline NO_ALIAS auto is_zero(const f32 v) noexcept->bool { return abs(v) < 1e-6f; } [[nodiscard]] inline NO_ALIAS auto is_one(const f32 v) noexcept->bool { return is_zero(v - 1.f); } [[nodiscard]] inline NO_ALIAS auto near_equal(const f32 a, const f32 b) noexcept->bool { if (is_zero(a - b)) return true; const s32 a2 = *reinterpret_cast<const s32*>(&a); const s32 b2 = *reinterpret_cast<const s32*>(&a); if (a2 < 0 != b2 < 0) return false; return abs(a2 - b2) <= 0b0100; } [[nodiscard]] constexpr NO_ALIAS auto within_epsilon(const f32 a, const f32 b, const f32 epsilon) noexcept->bool { const f32 num = a - b; return -epsilon <= num && num <= epsilon; }

Thanks, will have a look at this

Mar!o

Your welcome, just write if you need more help :)

Mar!o

Remember it is C++17 if you need it for C or an older std just write too

Pavel

Remember it is C++17 if you need it for C or an older std just write too

I need it exactly for C++17 :)

Mar!o

Alright :)

Álvaro

Hi everybody

klimi

Hi everybody

Hello

Anonymous

Hi everybody

Hello

Álvaro

Just entering this awesome world of C in 42Madrid

Álvaro

Hope learn a lot from you

klimi

Hope learn a lot from you

most things are up to you tho. You are the person who is so awesome to learn all the things

Álvaro

😊👍

Lauri

dayan: What getting memory location of variable can be used for Useful for

klimi

um changing the variable or reading it? (im no pro)

Lauri

No

klimi

okay.

MilkBeforeCereal

No

but essentially it is used for that? 🤔

Lauri

klimi

yes?

Lauri

What can I do with that memory adress

klimi

um changing the variable or reading it? (im no pro)

^

Mar!o

It is useful in many cases for example function parameters: A pointer is like an int, but it contains a memory adress. If you want to pass a big object to a function, it would copy the object from the callsite. If you pass a pointer it only copies the pointer and you can access the big data using the pointer

Mar!o

Which is of course much faster

桃桃乌龙

Learn yourself some assembly language and you’ll find out that pointers is pretty much everywhere.

Pavel

[[nodiscard]] inline NO_ALIAS auto is_zero(const f32 v) noexcept->bool { return abs(v) < 1e-6f; } [[nodiscard]] inline NO_ALIAS auto is_one(const f32 v) noexcept->bool { return is_zero(v - 1.f); } [[nodiscard]] inline NO_ALIAS auto near_equal(const f32 a, const f32 b) noexcept->bool { if (is_zero(a - b)) return true; const s32 a2 = *reinterpret_cast<const s32*>(&a); const s32 b2 = *reinterpret_cast<const s32*>(&a); if (a2 < 0 != b2 < 0) return false; return abs(a2 - b2) <= 0b0100; } [[nodiscard]] constexpr NO_ALIAS auto within_epsilon(const f32 a, const f32 b, const f32 epsilon) noexcept->bool { const f32 num = a - b; return -epsilon <= num && num <= epsilon; }

By the way, there seems to be a UB (at least in general case, where strict aliasing is enabled). Type punning between these values is violating the rules of strict aliasing. See the last code example in the Notes section https://en.cppreference.com/w/cpp/language/reinterpret_cast These lines const s32 a2 = *reinterpret_cast<const s32*>(&a); const s32 b2 = *reinterpret_cast<const s32*>(&a); can be replaced with these for example s32 a2, b2; memcpy(&a2, &a, sizeof(f32)); memcpy(&b2, &b, sizeof(f32)); More detailed explanation https://gist.github.com/shafik/848ae25ee209f698763cffee272a58f8

klimi

@bastyav you alright dude?

Mar!o

By the way, there seems to be a UB (at least in general case, where strict aliasing is enabled). Type punning between these values is violating the rules of strict aliasing. See the last code example in the Notes section https://en.cppreference.com/w/cpp/language/reinterpret_cast These lines const s32 a2 = *reinterpret_cast<const s32*>(&a); const s32 b2 = *reinterpret_cast<const s32*>(&a); can be replaced with these for example s32 a2, b2; memcpy(&a2, &a, sizeof(f32)); memcpy(&b2, &b, sizeof(f32)); More detailed explanation https://gist.github.com/shafik/848ae25ee209f698763cffee272a58f8

You are right the memcpy solution is better but the old one shouldn't be a ub because a2 and b2 are copies of the dereferenced punned pointer which are not affected by the address meaning that there is no aliasing second pointer to them. Gonna read the post tough :)

Pavel

You are right the memcpy solution is better but the old one shouldn't be a ub because a2 and b2 are copies of the dereferenced punned pointer which are not affected by the address meaning that there is no aliasing second pointer to them. Gonna read the post tough :)

Probably, but the compiler is free to do any wierd stuff in this case, so I would be at least aware of this BTW, I forgot to include one of the links (updated my message now) https://en.cppreference.com/w/cpp/language/reinterpret_cast

Mar!o

Probably, but the compiler is free to do any wierd stuff in this case, so I would be at least aware of this BTW, I forgot to include one of the links (updated my message now) https://en.cppreference.com/w/cpp/language/reinterpret_cast

And sometimes the compiler does really weird stuff :P

Idiriz906

I am human

Idiriz906

😭😭😭why the admins restricted me to write here-!!!!

Idiriz906

Would not i get here benifits from the experiers 😭😭

Artöm

Remember it is C++17 if you need it for C or an older std just write too

14 if remove nodiscard