Replace f64 with rust_decimal in token conversions

.changelog/unreleased/improvements/436-remove-f64.md

@@ -0,0 +1,2 @@
+- Refactored token decimal formatting.
+  ([#436](https://github.com/anoma/namada/pull/436))

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;
 

wasm/checksums.json

@@ -1,15 +1,18 @@
 {
-    "tx_bond.wasm": "tx_bond.04d6847800dad11990b42e8f2981a4a79d06d6d0c981c3d70c929e5b6a4f348b.wasm",
-    "tx_ibc.wasm": "tx_ibc.6ab530398ed8e276a8af7f231edbfae984b7e84eeb854714ba9339c5bed9d330.wasm",
-    "tx_init_account.wasm": "tx_init_account.578d987351e6ae42baa7849ae167e3ba33f3a62dba51cd47b0fa6d3ea6e4f128.wasm",
-    "tx_init_proposal.wasm": "tx_init_proposal.71e27610210622fa53c3de58351761cca839681a4f450d4eff6b46bde3ae85a5.wasm",
-    "tx_init_validator.wasm": "tx_init_validator.269f065ff683782db2fdcac6e2485e80cbebb98929671a42eeb01703e0bbd8f5.wasm",
-    "tx_transfer.wasm": "tx_transfer.784325cf7763faf8d75797960cda6fbabbd343f3c6f7e6785f60f5e0911a6bb5.wasm",
-    "tx_unbond.wasm": "tx_unbond.ed13fa636d138ac4e35f2b4f31a6b4d3bed67e6b998dc6325f90711a2aca3704.wasm",
-    "tx_update_vp.wasm": "tx_update_vp.c4050e597116203eba5afde946a014afb067bdeaaae417377214a80c38a3786b.wasm",
-    "tx_vote_proposal.wasm": "tx_vote_proposal.ece325881aad1c8a29f715c2f435c3335e08e51eed837c00ce0f7bbaddbefe50.wasm",
-    "tx_withdraw.wasm": "tx_withdraw.408fc10b3744c398258124e5e48e3449f6baf82a263df26911586a3382fbceb9.wasm",
-    "vp_testnet_faucet.wasm": "vp_testnet_faucet.ae9a681dc2c1bd244b0575474fa4a364af56fa75833950693ca52ab25018c97d.wasm",
-    "vp_token.wasm": "vp_token.468de153dc5ce3af208bd762de3e85be48bc631012ec5f0947af95168da6cb93.wasm",
-    "vp_user.wasm": "vp_user.c101016a85a72f40da7f33e5d9061cfd2e3274eaac75a71c59c9ab4ed9896ffd.wasm"
-}
+    "tx_bond.wasm": "tx_bond.059b1256240d15a64cf419f3a2d24af1496211c386d85acc3733095bc2e5da9b.wasm",
+    "tx_ibc.wasm": "tx_ibc.4eeb30bc1e6a32b8efe8958eab568082a238db01eb98340f28a9fa41371a3753.wasm",
+    "tx_init_account.wasm": "tx_init_account.85d017ac76e51f359fa07e753c0e6fcbd3341e7661492cbf2801cf3c41480dd4.wasm",
+    "tx_init_nft.wasm": "tx_init_nft.fbeb1687a364b2c249c9fd69588ff0985bd9c1f8f4c93e5328de1e9ba527d991.wasm",
+    "tx_init_proposal.wasm": "tx_init_proposal.43b52414649bb0fec86dfb35d001656c1825bc5906e450e8b0c3a60aaa5f3d45.wasm",
+    "tx_init_validator.wasm": "tx_init_validator.6ccb7fcf246cb7a2f97a5dfdcefe16ee1add72a832081c2572adc2d7a355cf56.wasm",
+    "tx_mint_nft.wasm": "tx_mint_nft.f2ed21521c676f04be4c6278cc60bec83265c3750437c87d9ea681b830767d71.wasm",
+    "tx_transfer.wasm": "tx_transfer.b6fc342f4a76918874e6d037a3864e4369dbba7cd7d558622e7a723e3d854da3.wasm",
+    "tx_unbond.wasm": "tx_unbond.6e7316d08bf8ab9a6fb1889f64a5a2265ee0399661dbb48e33555170545d1c7c.wasm",
+    "tx_update_vp.wasm": "tx_update_vp.6d291dadb43545a809ba33fe26582b7984c67c65f05e363a93dbc62e06a33484.wasm",
+    "tx_vote_proposal.wasm": "tx_vote_proposal.d0a87d58f64f46586ae3d83852deee269e22520f4780875c05aaf1731044c356.wasm",
+    "tx_withdraw.wasm": "tx_withdraw.e5dcc5ef2362018c1fa5ea02912528ee929aa7b6fefcf06f4ccf7509bfa52283.wasm",
+    "vp_nft.wasm": "vp_nft.9be5a821bc7b3075b917e8ead45893502d82cc7417e6af50dfd3f6baf36243e0.wasm",
+    "vp_testnet_faucet.wasm": "vp_testnet_faucet.8e2e45ff165d40dc8249188aca108e5cba86ac5dd1cd989b0237cadd4b66bfdf.wasm",
+    "vp_token.wasm": "vp_token.4a0446f20e7436de1e889c640a11644d1a1295c4d29e45b24582df2b9ed3176e.wasm",
+    "vp_user.wasm": "vp_user.eb1d6f1f524c28571ad0f21f75371aa635257313cea2702b9a70e5022fe6c3ef.wasm"
+}