How to store numbers greater than 2^64

fuel · December 15, 2022, 1:42am

Hi there! In continuation of “how to save strings in the storage of DApp topic” I thought about decimals. For example, I want to issue the ETH token with decimals 18, but the maximum number type in sway is u64 and that means I can use numbers till 2^18 = ~18.4467 * 1e18.
Is it possible to somehow use a larger type, or maybe it will be possible to store a large number as a string?

furnic · December 15, 2022, 3:55am

If you need really large numbers, the sway standard library has both U128 and U256 types available.

github.com

FuelLabs/sway/blob/50c1b6c858c044acf88760cb7eb1b39d076f322d/sway-lib-std/src/u256.sw#L26


      
          /// Right shift a u64 and preserve the overflow amount if any
          fn rsh_with_carry(word: u64, shift_amount: u64) -> (u64, u64) {
              let left_shift_amount = 64 - shift_amount;
              let carry = word << left_shift_amount;
              let shifted = word >> shift_amount;
              (shifted, carry)
          }
          
          
/// The 256-bit unsigned integer type.
          /// Represented as four 64-bit components: `(a, b, c, d)`, where `value = (a << 192) + (b << 128) + (c << 64) + d`.
          pub struct U256 {
              a: u64,
              b: u64,
              c: u64,
              d: u64,
          }
          
          
pub enum U256Error {
              LossOfPrecision: (),
          }

fuel · December 15, 2022, 9:48am

Thanks, will try to use U128 and U256

Fuelgasoline · December 15, 2022, 12:58pm

Thank for the question. I got it

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How to store numbers greater than 2^64

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