How to calculate square root of a number in ink! smart contract?

Question

In the classic flipper ink! sc example I tried within a function

let dist2: f32 = f32::sqrt(4.0);

and got the error " function or associated item not found in f32 "

Bearing in mind this https://doc.rust-lang.org/std/primitive.f32.html#method.sqrt and failing that, after installing and trying this https://crates.io/crates/sp-arithmetic that I found here What's the best way to compute square root in Substrate? but creates conflicts and fails to compile flipper.

I am puzzled of how to proceed. Any suggestions please?

Answer 1

Issue is now resolved. As suggested by Phala team adding the following in the Cargo.toml

[dependencies] 
... 
sp-arithmetic = { version = "15", default-features = false }

[features] 
std = [ 
... 
"sp-arithmetic/std"
]

And

    [profile.release] 
    overflow-checks = false

And following this post Ink! smart contract struct field issues for necessary type conversions

Flipper now runs fine

   use scale::CompactAs; 
   use sp_arithmetic::FixedU128; 

   #[ink(message)] 
   pub fn get_squareroot(&self, num: u32) -> u128 {  
       let d1 = FixedU128::from_u32(num);  
       let d2 = FixedU128::sqrt(d1); 
       let d3 = *d2.encode_as();
       d3 
    }

Answer 2

ink! smart contract doesn't support f32 type. You can get more info from here

Answer 3

`use ink_lang::contract;

#[contract] mod sqrt_contract { #[ink(storage)] pub struct SqrtContract {}

impl SqrtContract {
    #[ink(constructor)]
    pub fn new() -> Self {
        Self {}
    }

    #[ink(message)]
    pub fn calculate_sqrt(&self, num: u64) -> u64 {
        ink_core::math::sqrt(num)
    }
}

}`

Keep in mind that Ink! is a statically-typed language, so you'll need to specify the data type of the input and output values. Also note that the sqrt function may not be available in all versions of Ink!, so make sure to check the documentation for your specific version.