V: Imprecise double arithmetics?

[MaxGraey]

fn main() {
    t := 0.1 + 0.2
    println(t == 0.30000000000000004)
}

Output: false
Expected: true

[medvednikov]

https://play.golang.org/p/NAFwcLhTQK0

[MaxGraey]

In Go: 0.1 + 0.2 == 0.3 and it's true. Btw it's wrong! In all mature languages which follow IEEE 754 standard this should be false!

1. Go true
2. Rust false
3. C false

But in your case even 0.1 + 0.2 == 0.3 is false:

fn main() {
    t := 0.1 + 0.2
    println(t == 0.3)
}

Output: false

How you explain this?

[medvednikov]

V running in the playground compiles to C, that's how it works there.

[MaxGraey]

@medvednikov
Same result as in Rust:
https://onlinegdb.com/BkdNxHYtV

[medvednikov]

Right now floating-point constants default to f32, instead of f64. Will be fixed today.

[medvednikov]

I changed it to f64, the comparison still doesn't work because it doesn't work in C (and in C++).

Comparing floats like this is a bad idea:

https://www.cs.technion.ac.il/users/yechiel/c++-faq/floating-point-arith.html

https://www.boost.org/doc/libs/1_61_0/libs/math/doc/html/math_toolkit/float_comparison.html

[medvednikov]

Actually 0.1 + 0.2 == 0.30000000000000004 works now. 0.1 + 0.2 == 0.3 doesn't.

[MaxGraey]

the comparison still doesn't work because it doesn't work in C (and in C++).

comparison 0.1 + 0.2 == 0.30000000000000004 should works exactly in C/C++:

Current in V:

fn main() {
    t := 0.1 + 0.2
    println(t == 0.30000000000000004)
}

Output:

It still not fixed!

[MaxGraey]

In Rust:

[MaxGraey]

In Go:

[medvednikov]

Forgot to deploy the playground after the fix:

t := 0.1 + 0.2
println(t == 0.30000000000000004)
// true

Now it works like C/C++.

[proyb6]

I tried to run on playground today, output as false

t := 0.1 + 0.2
println(t == 0.30000000000000004)
// t is 0.300000

[MaxGraey]

Can confirm. This issue still not fixed!

[whoizit]

it should be open, because this is not fixed

[medvednikov]

@whoizit fixed again.

t == 0.30000000000000004

[megatux]

Just for completion, https://0.30000000000000004.com/