[WIP ]20085 benchmarks

docs/build/building-modules/18-decimal-handling.md

@@ -0,0 +1,129 @@
+---
+sidebar_position: 1
+---
+# Decimal Handling in Cosmos SDK
+
+## Introduction
+
+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:
+
+* **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.
+
+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.
+
+## Why the Change?
+
+* **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`.`
+
+## Using `Dec` in Modules that haven't used `LegacyDec`
+
+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.
+
+As an example, we will use `DecCoin` which is a common type used in the Cosmos SDK.
+
+
+```protobuf
+message DecCoin {
+  option (gogoproto.equal) = true;
+
+  string denom  = 1;
+  string amount = 2 [
+    (cosmos_proto.scalar)  = "cosmos.Dec",
+    (gogoproto.customtype) = "cosmossdk.io/math.Dec",
+    (gogoproto.nullable)   = false
+  ];
+}
+```
+
+How you can implement `Dec` in your module:
+
+```go
+import (
+	"cosmossdk.io/math"
+)
+
+example := math.NewDecFromInt64(100)
+```
+
+## Modules migrating from `LegacyDec` to `Dec`
+
+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.**
+
+## Precision Handling
+
+The reason for the state breaking change is the difference in precision handling between the two decimal types:
+
+* **LegacyDec**: Fixed precision of 18 decimal places.
+* **Dec**: Flexible precision up to 34 decimal places using the apd library.
+
+## Byte Representation Changes Example
+
+The change in precision handling directly impacts the byte representation of decimal values:
+
+**Legacy Dec Byte Representation:**
+`2333435363738393030303030303030303030303030303030303030`
+
+This example includes the value 123456789 followed by 18 zeros to maintain the fixed precision.
+
+**New Dec Byte Representation:**
+`0a03617364121031323334353637383900000000000000`
+
+This example shows the value 123456789 without additional padding, reflecting the flexible precision handling of the new Dec type.
+
+## Impact of Precision Change
+
+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.
+
+## Example of State-Breaking Change
+
+The protobuf definitions for DecCoin illustrate the change in the custom type for the amount field.
+
+**Before:**
+
+```protobuf
+message DecCoin {
+  option (gogoproto.equal) = true;
+
+  string denom  = 1;
+  string amount = 2 [
+    (cosmos_proto.scalar)  = "cosmos.Dec",
+    (gogoproto.customtype) = "cosmossdk.io/math.LegacyDec",
+    (gogoproto.nullable)   = false
+  ];
+}
+```
+
+**After:**
+
+```protobuf
+message DecCoin {
+  option (gogoproto.equal) = true;
+
+  string denom  = 1;
+  string amount = 2 [
+    (cosmos_proto.scalar)  = "cosmos.Dec",
+    (gogoproto.customtype) = "cosmossdk.io/math.Dec",
+    (gogoproto.nullable)   = false
+  ];
+}
+```
+
+## Converting `LegacyDec` to `Dec` without storing the data
+
+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.
+
+```go
+func LegacyDecToDec(ld LegacyDec) (Dec, error) {
+    return NewDecFromString(ld.String())
+}
+```
+
+```go
+func DecToLegacyDec(ld Dec) (LegacyDec, error) {
+    return LegacyDecFromString(ld.String())
+}
+```
+

go.mod

@@ -189,6 +189,7 @@ replace (
 	cosmossdk.io/depinject => ./depinject
 	cosmossdk.io/log => ./log
 	cosmossdk.io/store => ./store
+	cosmossdk.io/math => ./math
 	cosmossdk.io/x/accounts => ./x/accounts
 	cosmossdk.io/x/auth => ./x/auth
 	cosmossdk.io/x/bank => ./x/bank