support for negative numbers in Decimal from @cosmjs/math

[stalniy]

Description

The Decimal class from @cosmjs/math currently rejects negative values and throws an error when the input contains a "-" sign.
This makes it impossible to represent or work with signed decimal numbers in CosmJS.

🔍 Example

import { Decimal } from "@cosmjs/math";

Decimal.fromUserInput("-0.123", 3);
// ❌ Error: Negative values not supported

💡 Expected behavior

Decimal should support negative values, or at least provide an alternative (e.g. SignedDecimal) for cases where signed arithmetic is required.

🧠 Context

In the Go Cosmos SDK, the equivalent type sdk.Dec does support negative numbers.
This is useful for many valid scenarios, such as:

• Calculating deltas or differences between balances or prices
• Expressing signed ratios or deviations
• Performing off-chain accounting or simulation logic

In CosmJS, however, the current implementation appears to be limited to non-negative quantities (like tokens, gas prices, etc.), which restricts flexibility in analytical or off-chain use cases.

🚀 Proposal

• Extend the existing Decimal class to allow negative values, or
• Introduce a new SignedDecimal type that:
  • Keeps the same precision handling
  • Encodes/decodes safely
  • Maintains backward compatibility with positive-only decimals

[webmaster128]

Interesting. I also just found hyperweb-io/telescope#642.

Decimal was never written for the Cosmos SDK type github.com/cosmos/cosmos-sdk/types.Dec. It was meant to make writong dapps with balances easier and avoid add the rounding issues that number has, especially for displaying balances. We also have explicitly "A type for arbitrary precision, non-negative decimals." in the type description.

Not sure what the best solution is here. The entire design right now is made for Coin.

[stalniy]

I see. Well, I found a simple workaround for my usecase.

However support for negative values could be useful for some requirements in akash which may arise in the future but I dont have enough details to insist on implementing negative decimals support.

Cc: @troian

[webmaster128]

After #1916 the Decimal type is pretty much fully migrated from string to bigint. This should make it easy to add extra tests and remove the restriction to non-negative values.

[webmaster128]

Could you review #1930?