This bigdecimal library in Rust: https://github.com/akubera/bigdecimal-rs is used like this: use bigdecimal::BigDecimal; use std::str::FromStr; fn main() { let input = std::env::args().skip(1).next().unwrap_or("0.7".to_string()); let decimal = BigDecimal::from_str(&input).expect("invalid d…

I can't help but link to this post: How to write slow Rust code

from the post it isn't clear if the problem is in lazy_static or in the initialization of the big int from a number instead of from a word. Should I initialize all of them every time I need them? Looks like parsing a string every time I need the number is not ok.

The post suggests using an ordinary integer whenever you need to use seven in an operation, since BigDecimal supports operators where the other side is an ordinary integer.

Aren't you confusing BigDecimal with BigInt? Because I can't with BigDecimal

Strangely, BigDecimal implements Div with primitive integers, but not Mul, Add, Sub, etc.

why there is a problem with lazy_static? I don't see any obvious penalties

the strange thing is that n = (&DEC_SEVEN - x); gives error[E0369]: cannot subtract `&BigDecimal` from `&DEC_SEVEN` --> src/math.rs:43:25 | 43 | n = (&DEC_SEVEN - x); | ---------- ^ - &BigDecimal | | | &DEC_SEVEN | = note: an impl…

It's probably because lazy_static! is introducing a wrapper type around it. Try &*DEC_SEVEN to get a reference to the inner value.

indeed it works. So this is the penalty, this wrapper type? Should I instead make an instantiable object that generates the big decimals on the first run? This is odd for math functions but I think this is the only way to make it fast

How to have a global BigDecimal value in Rust

help

cuviper August 24, 2021, 4:54pm 2

You can use lazy_static or once_cell::sync::Lazy.

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How to have a global BigDecimal value in Rust

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