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feat(math): Upstream GDA based decimal type v2 #20536
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update dec w benchmark testing
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fix version
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feat(math): Testing Sub for GDA Dec Type (#20626)
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feat(math): Upstream GDA based decimal type - Add function coverage (…
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feat(math): Upstream GDA based decimal type testing (#20763)
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feat(math): Upstream GDA based decimal type (docs) (#20950)
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| --- | ||
| # Decimal Handling in Cosmos SDK | ||
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| ## Introduction | ||
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| In the Cosmos SDK, there are two types of decimals: `LegacyDec` and `Dec`. `LegacyDec` is the older decimal type that is still available for use, while `Dec` is the newer, more performant decimal type. The implementation of `Dec` is adapted from Regen Network's `regen-ledger`, specifically from [this module](https://github.com/regen-network/regen-ledger/tree/main/types/math). Migrating from `LegacyDec` to `Dec` involves state-breaking changes, specifically: | ||
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| * **Data Format**: The internal representation of decimals changes, affecting how data is stored and processed. | ||
| * **Precision Handling**: `Dec` supports flexible precision up to 34 decimal places, unlike `LegacyDec` which has a fixed precision of 18 decimal places. | ||
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| These changes require a state migration to update existing decimal values to the new format. It is recommended to use `Dec` for new modules to leverage its enhanced performance and flexibility. | ||
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| ## Why the Change? | ||
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| * **Enhanced Precision**: `Dec` uses the [apd](https://github.com/cockroachdb/apd) library for arbitrary precision decimals, suitable for accurate financial calculations. | ||
| * **Immutable Operations**: `Dec` operations are safer for concurrent use as they do not mutate the original values. | ||
| * **Better Performance**: `Dec` operations are faster and more efficient than `LegacyDec`.` | ||
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| ## Using `Dec` in Modules that haven't used `LegacyDec` | ||
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| If you are creating a new module or updating an existing module that has not used `LegacyDec`, you can directly use `Dec` without any changes. | ||
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| As an example we will use `DecCoin` which is a common type used in the Cosmos SDK. | ||
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| ```protobuf | ||
| message DecCoin { | ||
| option (gogoproto.equal) = true; | ||
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| string denom = 1; | ||
| string amount = 2 [ | ||
| (cosmos_proto.scalar) = "cosmos.Dec", | ||
| (gogoproto.customtype) = "cosmossdk.io/math.Dec", | ||
| (gogoproto.nullable) = false | ||
| ]; | ||
| } | ||
| ``` | ||
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| How you can implement `Dec` in your module: | ||
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| ```go | ||
| import ( | ||
| "cosmossdk.io/math" | ||
| ) | ||
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| example := math.NewDecFromInt64(100) | ||
| ``` | ||
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| ## Modules migrating from `LegacyDec` to `Dec` | ||
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| When migrating from `LegacyDec` to `Dec`, you need to update your module to use the new decimal type. **These types are state breaking changes and require a migration.** | ||
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| ## Precision Handling | ||
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| The reason for the state breaking change is the difference in precision handling between the two decimal types: | ||
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| * **LegacyDec**: Fixed precision of 18 decimal places. | ||
| * **Dec**: Flexible precision up to 34 decimal places using the apd library. | ||
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| ## Byte Representation Changes Example | ||
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| The change in precision handling directly impacts the byte representation of decimal values: | ||
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| **Legacy Dec Byte Representation:** | ||
| `2333435363738393030303030303030303030303030303030303030` | ||
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| This example includes the value 123456789 followed by 18 zeros to maintain the fixed precision. | ||
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| **New Dec Byte Representation:** | ||
| `0a03617364121031323334353637383900000000000000` | ||
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| This example shows the value 123456789 without additional padding, reflecting the flexible precision handling of the new Dec type. | ||
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| ## Impact of Precision Change | ||
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| The increase in precision from 18 to 34 decimal places allows for more detailed decimal values but requires data migration. This change in how data is formatted and stored is a key aspect of why the transition is considered state-breaking. | ||
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| ## Example of State-Breaking Change | ||
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| The protobuf definitions for DecCoin illustrate the change in the custom type for the amount field. | ||
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| **Before:** | ||
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| ```protobuf | ||
| message DecCoin { | ||
| option (gogoproto.equal) = true; | ||
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| string denom = 1; | ||
| string amount = 2 [ | ||
| (cosmos_proto.scalar) = "cosmos.Dec", | ||
| (gogoproto.customtype) = "cosmossdk.io/math.LegacyDec", | ||
| (gogoproto.nullable) = false | ||
| ]; | ||
| } | ||
| ``` | ||
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| **After:** | ||
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| ```protobuf | ||
| message DecCoin { | ||
| option (gogoproto.equal) = true; | ||
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| string denom = 1; | ||
| string amount = 2 [ | ||
| (cosmos_proto.scalar) = "cosmos.Dec", | ||
| (gogoproto.customtype) = "cosmossdk.io/math.Dec", | ||
| (gogoproto.nullable) = false | ||
| ]; | ||
| } | ||
| ``` | ||
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| ## Converting `LegacyDec` to `Dec` without storing the data | ||
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| If you would like to convert a `LegacyDec` to a `Dec` without a state migration changing how the data is handled internally within the application logic and not how it's stored or represented. You can use the following methods. | ||
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| ```go | ||
| func LegacyDecToDec(ld LegacyDec) (Dec, error) { | ||
| return NewDecFromString(ld.String()) | ||
| } | ||
| ``` | ||
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| ```go | ||
| func DecToLegacyDec(ld Dec) (LegacyDec, error) { | ||
| return LegacyDecFromString(ld.String()) | ||
| } | ||
| ``` | ||
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