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feat(math): Upstream GDA based decimal type #20085

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update dec w benchmark testing
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61 changes: 61 additions & 0 deletions docs/build/building-modules/18-decimal-handling.md
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---
sidebar_position: 1
---
# Decimal Handling in Cosmos SDK

:::note
As part of ongoing improvements to the Cosmos SDK, we have updated our decimal handling from `LegacyDec` to `Dec`. This update is crucial for modules that perform mathematical computations, ensuring higher precision and better performance.
:::

## Introduction

In the Cosmos SDK we have 2 types of decimals LegacyDec and Dec. `LegacyDec` is the old decimal type that was used, which is still available. `Dec` is the new decimal type and is more performant than `LegacyDec`.

## 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.
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* **Better Performance**: `Dec` operations are faster and more efficient than `LegacyDec`.
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Very good to explain the motivation!


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Benchmarking results below between `LegacyDec` and `Dec`:

```
BenchmarkCompareLegacyDecAndNewDec/LegacyDec-10 8621032 143.8 ns/op 144 B/op 3 allocs/op
BenchmarkCompareLegacyDecAndNewDec/NewDec-10 5206173 238.7 ns/op 176 B/op 7 allocs/op
BenchmarkCompareLegacyDecAndNewDecQuoInteger/LegacyDec-10 5767692 205.1 ns/op 232 B/op 6 allocs/op
BenchmarkCompareLegacyDecAndNewDecQuoInteger/NewDec-10 23172602 51.75 ns/op 16 B/op 2 allocs/op
BenchmarkCompareLegacyAddAndDecAdd/LegacyDec-10 21157941 56.33 ns/op 80 B/op 2 allocs/op
BenchmarkCompareLegacyAddAndDecAdd/NewDec-10 24133659 48.92 ns/op 48 B/op 1 allocs/op
BenchmarkCompareLegacySubAndDecMul/LegacyDec-10 14256832 87.47 ns/op 80 B/op 2 allocs/op
BenchmarkCompareLegacySubAndDecMul/NewDec-10 18273994 65.68 ns/op 48 B/op 1 allocs/op
BenchmarkCompareLegacySubAndDecSub/LegacyDec-10 19988325 64.46 ns/op 80 B/op 2 allocs/op
BenchmarkCompareLegacySubAndDecSub/NewDec-10 27430347 42.45 ns/op 8 B/op 1 allocs/op
```
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Replace hard tabs with spaces in the benchmarking code block for consistency with Markdown formatting standards.


## Updating Your Modules

Modules using `LegacyDec` should transition to `Dec` to maintain compatibility with the latest SDK updates. This involves:

1. Updating type declarations from `LegacyDec` to `Dec`.
2. Modifying arithmetic operations to handle the new method signatures and potential errors.

# Example Update

Transitioning an addition operation from `LegacyDec` to `Dec`:

**Before:**

```go
result := legacyDec1.Add(legacyDec2)
```

**After:**

```go
result, err := dec1.Add(dec2)
if err != nil {
log.Fatalf("Error during addition: %v", err)
}
```

This can be done for all arithmetic operations, including subtraction, multiplication, division, and more.
2 changes: 2 additions & 0 deletions go.mod
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Expand Up @@ -80,6 +80,7 @@ require (
github.com/cenkalti/backoff/v4 v4.1.3 // indirect
github.com/cespare/xxhash v1.1.0 // indirect
github.com/cespare/xxhash/v2 v2.2.0 // indirect
github.com/cockroachdb/apd/v2 v2.0.2 // indirect
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Curious why we landed on apd v2 instead of v3? Didn't see a discussion in either of #7773 (comment) or #11783 , just a brief mention. In some testing we did it showed 20-30% better performance improvements in overall runtime.

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@aaronc aaronc May 13, 2024 •
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This just looks like an oversight. The reference code was written a while ago (before v3) and this code should be updated to use the latest version

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Cool, thanks for the insight.

github.com/cockroachdb/logtags v0.0.0-20230118201751-21c54148d20b // indirect
github.com/cockroachdb/pebble v1.1.0 // indirect
github.com/cockroachdb/redact v1.1.5 // indirect
Expand Down Expand Up @@ -183,6 +184,7 @@ replace (
cosmossdk.io/api => ./api
cosmossdk.io/core => ./core
cosmossdk.io/depinject => ./depinject
cosmossdk.io/math => ./math
cosmossdk.io/x/accounts => ./x/accounts
cosmossdk.io/x/auth => ./x/auth
cosmossdk.io/x/bank => ./x/bank
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2 changes: 2 additions & 0 deletions go.sum
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Expand Up @@ -107,6 +107,8 @@ github.com/cncf/xds/go v0.0.0-20210805033703-aa0b78936158/go.mod h1:eXthEFrGJvWH
github.com/cncf/xds/go v0.0.0-20210922020428-25de7278fc84/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
github.com/cncf/xds/go v0.0.0-20211001041855-01bcc9b48dfe/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
github.com/cncf/xds/go v0.0.0-20211011173535-cb28da3451f1/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
github.com/cockroachdb/apd/v2 v2.0.2 h1:weh8u7Cneje73dDh+2tEVLUvyBc89iwepWCD8b8034E=
github.com/cockroachdb/apd/v2 v2.0.2/go.mod h1:DDxRlzC2lo3/vSlmSoS7JkqbbrARPuFOGr0B9pvN3Gw=
github.com/cockroachdb/datadriven v0.0.0-20190809214429-80d97fb3cbaa/go.mod h1:zn76sxSg3SzpJ0PPJaLDCu+Bu0Lg3sKTORVIj19EIF8=
github.com/cockroachdb/datadriven v1.0.3-0.20230413201302-be42291fc80f h1:otljaYPt5hWxV3MUfO5dFPFiOXg9CyG5/kCfayTqsJ4=
github.com/cockroachdb/datadriven v1.0.3-0.20230413201302-be42291fc80f/go.mod h1:a9RdTaap04u637JoCzcUoIcDmvwSUtcUFtT/C3kJlTU=
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