replace floating point arithm from token module with rust_decimal

proof_of_stake/src/parameters.rs

@@ -71,11 +71,14 @@ pub enum ValidationError {
     UnbondingLenTooShort(u64, u64),
 }
 
+/// The number of fundamental units per whole token of the native staking token
+pub const TOKENS_PER_NAM: u64 = 1_000_000;
+
 /// From Tendermint: <https://github.com/tendermint/tendermint/blob/master/spec/abci/apps.md#updating-the-validator-set>
 const MAX_TOTAL_VOTING_POWER: i64 = i64::MAX / 8;
 
 /// Assuming token amount is `u64` in micro units.
-const TOKEN_MAX_AMOUNT: u64 = u64::MAX / 1_000_000;
+const TOKEN_MAX_AMOUNT: u64 = u64::MAX / TOKENS_PER_NAM;
 
 impl PosParams {
     /// Validate PoS parameters values. Returns an empty list if the values are

shared/src/types/token.rs

@@ -6,6 +6,7 @@ use std::ops::{Add, AddAssign, Mul, Sub, SubAssign};
 use std::str::FromStr;
 
 use borsh::{BorshDeserialize, BorshSchema, BorshSerialize};
+use rust_decimal::prelude::{Decimal, ToPrimitive};
 use serde::{Deserialize, Serialize};
 use thiserror::Error;
 
@@ -37,7 +38,6 @@ pub struct Amount {
 pub const MAX_DECIMAL_PLACES: u32 = 6;
 /// Decimal scale of token [`Amount`] and [`Change`].
 pub const SCALE: u64 = 1_000_000;
-const SCALE_F64: f64 = SCALE as f64;
 
 /// A change in tokens amount
 pub type Change = i128;
@@ -109,21 +109,16 @@ impl<'de> serde::Deserialize<'de> for Amount {
     }
 }
 
-impl From<Amount> for f64 {
-    /// Warning: `f64` loses precision and it should not be used when exact
-    /// values are required.
+impl From<Amount> for Decimal {
     fn from(amount: Amount) -> Self {
-        amount.micro as f64 / SCALE_F64
+        Into::<Decimal>::into(amount.micro) / Into::<Decimal>::into(SCALE)
     }
 }
 
-impl From<f64> for Amount {
-    /// Warning: `f64` loses precision and it should not be used when exact
-    /// values are required.
-    fn from(micro: f64) -> Self {
-        Self {
-            micro: (micro * SCALE_F64).round() as u64,
-        }
+impl From<Decimal> for Amount {
+    fn from(micro: Decimal) -> Self {
+        let res = (micro * Into::<Decimal>::into(SCALE)).to_u64().unwrap();
+        Self { micro: res }
     }
 }
 
@@ -205,7 +200,7 @@ impl FromStr for Amount {
         match rust_decimal::Decimal::from_str(s) {
             Ok(decimal) => {
                 let scale = decimal.scale();
-                if scale > 6 {
+                if scale > MAX_DECIMAL_PLACES {
                     return Err(AmountParseError::ScaleTooLarge(scale));
                 }
                 let whole =
@@ -440,11 +435,11 @@ mod tests {
             /// The upper limit is set to `2^51`, because then the float is
             /// starting to lose precision.
             #[test]
-            fn test_token_amount_f64_conversion(raw_amount in 0..2_u64.pow(51)) {
+            fn test_token_amount_decimal_conversion(raw_amount in 0..2_u64.pow(51)) {
                 let amount = Amount::from(raw_amount);
-                // A round-trip conversion to and from f64 should be an identity
-                let float = f64::from(amount);
-                let identity = Amount::from(float);
+                // A round-trip conversion to and from Decimal should be an identity
+                let decimal = Decimal::from(amount);
+                let identity = Amount::from(decimal);
                 assert_eq!(amount, identity);
         }
     }

tests/src/native_vp/pos.rs

@@ -594,6 +594,10 @@ pub mod testing {
 
     use crate::tx::{self, tx_host_env};
 
+    const TOKENS_PER_NAM: i128 =
+        namada::ledger::pos::namada_proof_of_stake::parameters::TOKENS_PER_NAM
+            as i128;
+
     #[derive(Clone, Debug, Default)]
     pub struct TestValidator {
         pub address: Option<Address>,
@@ -940,9 +944,9 @@ pub mod testing {
                     // We convert the tokens from micro units to whole tokens
                     // with division by 10^6
                     let vp_before =
-                        params.votes_per_token * ((total_delta) / 1_000_000);
+                        params.votes_per_token * (total_delta / TOKENS_PER_NAM);
                     let vp_after = params.votes_per_token
-                        * ((total_delta + token_delta) / 1_000_000);
+                        * ((total_delta + token_delta) / TOKENS_PER_NAM);
                     // voting power delta
                     let vp_delta = vp_after - vp_before;
 
@@ -1001,12 +1005,12 @@ pub mod testing {
                         let total_delta = validator_total_deltas
                             .get(epoch)
                             .unwrap_or_default();
-                        // We convert the tokens from micro units to whole
+                        // We convert the tokens from micro units to whole 
                         // tokens with division by 10^6
                         let vp_before = params.votes_per_token
-                            * ((total_delta) / 1_000_000);
+                            * (total_delta / TOKENS_PER_NAM);
                         let vp_after = params.votes_per_token
-                            * ((total_delta + token_delta) / 1_000_000);
+                            * ((total_delta + token_delta) / TOKENS_PER_NAM);
                         // voting power delta
                         let vp_delta_at_unbonding =
                             vp_after - vp_before - vp_delta - total_vp_delta;
@@ -1080,9 +1084,9 @@ pub mod testing {
                     // We convert the tokens from micro units to whole tokens
                     // with division by 10^6
                     let vp_before = params.votes_per_token
-                        * ((total_delta_cur) / 1_000_000);
+                        * (total_delta_cur / TOKENS_PER_NAM);
                     let vp_after = params.votes_per_token
-                        * ((total_delta_cur + token_delta) / 1_000_000);
+                        * ((total_delta_cur + token_delta) / TOKENS_PER_NAM);
                     // voting power delta
                     let vp_delta = vp_after - vp_before;