how to treat u256 in ink?

Question

I want to use U256 in ink! but I've got some a error although I imported primitive_types/std.... how can I solve it?

use primitive_types::U256;

pub mod liquidity_num {
    pub const MIN_TICK: i32 = -887272;
    pub const MAX_TICK: i32 = -MIN_TICK;
    pub const MIN_SQRT_RATIO: u128 = 4295128739;
    pub const MAX_SQRT_RATIO: U256 = U256::from(1461446703485210103287273052203988822378723970342);
}

error

error: integer literal is too large
  --> uniswap-v3/logics/helpers/liquidity_helper.rs:13:49
   |
13 |     pub const MAX_SQRT_RATIO: U256 = U256::from(1461446703485210103287273052203988822378723970342);
   |                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0412]: cannot find type `U256` in this scope
  --> uniswap-v3/logics/helpers/liquidity_helper.rs:13:31
   |
13 |     pub const MAX_SQRT_RATIO: U256 = U256::from(1461446703485210103287273052203988822378723970342);
   |                               ^^^^ not found in this scope
   |
help: consider importing one of these items
   |
10 |     use crate::helpers::liquidity_helper::U256;
   |
10 |     use primitive_types::U256;
   |

error[E0433]: failed to resolve: use of undeclared type `U256`
  --> uniswap-v3/logics/helpers/liquidity_helper.rs:13:38
   |
13 |     pub const MAX_SQRT_RATIO: U256 = U256::from(1461446703485210103287273052203988822378723970342);
   |                                      ^^^^ not found in this scope
   |
help: consider importing one of these items
   |
10 |     use crate::helpers::liquidity_helper::U256;
   |
10 |     use primitive_types::U256;
   |

Answer 1

The largest size ink! has built in is a u128. ink! compiles to Wasm. The largest primitive Wasm has is 64bit (due to most computers using 64bit). So, there is no benefit to using any larger primitive over a collection.

From the ink! docs https://use.ink/ink-vs-solidity#uint256 the recommended way to treat with u256 is:

it is recommended to, with discretion, determine the range of the value, and choose the appropriate size (u8, u16, u32, u64, u128). If a 256-bit hash value is required, ink! has a Hash primitive available. In the event a value needs to be 256-bit, it is recommended to use an array (e.g. [u64; 4]).

See this old question on StackExchange too: Best way to handle Solidity's `uint256` in ink!