Expose toFixedDecimal

[0xgleb]

Motivation

We need to be able to convert floats into U256 so that when a user clicks "Max" in the withdrawal flow the amount gets displayed correctly in the form

Solution

Expose toFixedDecimal for use in the js lib

Checks

By submitting this for review, I'm confirming I've done the following:

• made this PR as small as possible
• unit-tested any new functionality
• linked any relevant issues or PRs
• included screenshots (if this involves a front-end change)

Summary by CodeRabbit

• New Features

  • Added the ability to convert floating-point values to fixed-point decimal strings with a specified number of decimals via the JavaScript API.
  • Introduced a new contract function for converting floats to fixed-point decimal values for offchain use.

• Tests

  • Added tests to verify correct conversion to fixed-point decimals and roundtrip consistency between float and fixed decimal representations.

[coderabbitai]

Walkthrough

A new method for converting a Float to a fixed-point decimal representation was introduced in both the Rust and Solidity codebases. This includes Rust-side logic, JavaScript API exposure, a Solidity contract method, and corresponding tests for both Rust and JavaScript to verify the conversion and its roundtrip behavior.

Changes

File(s)	Change Summary
crates/float/src/lib.rs	Added to_fixed_decimal method to Float for converting to fixed decimal; added and extended tests for coverage.
crates/float/src/js_api.rs	Added to_fixed_decimal_js method to expose fixed decimal conversion via the JS API, with documentation/example.
src/concrete/DecimalFloat.sol	Added toFixedDecimalLossless external pure function to expose fixed decimal conversion in Solidity contract.
test_js/float.test.ts	Added tests for toFixedDecimal and roundtrip with fromFixedDecimal in the JS bindings test suite.

Sequence Diagram(s)

sequenceDiagram
    participant JS/TS
    participant Rust Float
    participant Solidity Contract

    JS/TS->>Rust Float: to_fixed_decimal_js(decimals)
    Rust Float->>Rust Float: to_fixed_decimal(decimals)
    Rust Float->>Solidity Contract: toFixedDecimalLosslessCall(Float, decimals)
    Solidity Contract-->>Rust Float: U256 fixed decimal value
    Rust Float-->>JS/TS: String(fixed decimal)

Loading

Possibly related PRs

• Expose fromFixedDecimalLosslessPacked #68: Adds the inverse from_fixed_decimal method to the Float struct, closely related as it implements the opposite direction of fixed decimal conversion.
• create rust float lib #46: Introduces the initial Rust Float library and EVM contract integration, providing the foundation for the new conversion methods.

Suggested reviewers

• findolor
• hardyjosh

---

📜 Recent review details

Configuration used: CodeRabbit UI
Review profile: ASSERTIVE
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 08002d3 and 7a00af8.

📒 Files selected for processing (4)

• crates/float/src/js_api.rs (1 hunks)
• crates/float/src/lib.rs (4 hunks)
• src/concrete/DecimalFloat.sol (1 hunks)
• test_js/float.test.ts (1 hunks)

🧰 Additional context used

🧠 Learnings (5)

📓 Common learnings

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#59
File: crates/float/src/lib.rs:233-242
Timestamp: 2025-06-17T10:17:56.205Z
Learning: In the rainlanguage/rain.math.float repository, the maintainer 0xgleb prefers to handle documentation additions and improvements in separate issues rather than inline with feature PRs.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#58
File: src/concrete/DecimalFloat.sol:175-182
Timestamp: 2025-06-16T13:17:28.513Z
Learning: In the rainlanguage/rain.math.float codebase, there's an established naming convention where functions accepting a `Float` type parameter consistently use `float` as the parameter name, even though it shadows the type name. This pattern is used throughout `LibDecimalFloat.sol` and should be maintained for consistency in related contracts like `DecimalFloat.sol`.

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#30
File: test/src/lib/LibDecimalFloat.gt.t.sol:33-36
Timestamp: 2025-04-25T03:58:01.307Z
Learning: In the rain.math.float library, all values of `Float` (which is a type alias for bytes32) are considered valid and can be safely used with methods like gt(), lt(), or eq() without causing reverts.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#64
File: src/concrete/DecimalFloat.sol:0-0
Timestamp: 2025-06-17T10:02:01.394Z
Learning: In the rain.math.float project, the Float type is designed with a specific bit layout: 224-bit signed coefficient and 32-bit signed exponent, represented as 32 bytes total. The LibDecimalFloat.unpack function returns values that are guaranteed to fit within int224 and int32 ranges due to this internal representation, making explicit range checks before casting unnecessary.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#64
File: src/concrete/DecimalFloat.sol:0-0
Timestamp: 2025-06-17T10:02:01.394Z
Learning: In the rain.math.float project, the Float type is designed with a specific bit layout: 224-bit signed coefficient and 32-bit signed exponent, represented as 32 bytes total. The LibDecimalFloat.unpack function returns values that are guaranteed to fit within int224 and int32 ranges due to this internal representation, making explicit range checks before casting unnecessary.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#70
File: crates/float/src/evm.rs:38-43
Timestamp: 2025-07-03T11:20:50.456Z
Learning: In the rainlanguage/rain.math.float codebase, the user 0xgleb prefers not to add explanatory comments for well-established Rust idioms like the double `?` pattern, as these are self-explanatory to experienced Rust developers and don't need over-commenting.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#57
File: crates/float/src/lib.rs:316-328
Timestamp: 2025-06-18T09:10:41.740Z
Learning: In the rain.math.float codebase, the user prefers implementing standard Rust traits (like Neg) rather than creating redundant public methods when the trait already provides the needed functionality. Float implements Copy, so reference usage with operators is not a concern.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#58
File: crates/float/src/lib.rs:201-232
Timestamp: 2025-06-16T13:14:38.431Z
Learning: In the rain.math.float Rust crate, the `execute_call` function already provides sufficient abstraction for EVM contract calls by handling execution boilerplate, error handling, and result processing. Individual methods like `lt`, `eq`, `gt` only need to handle their specific call encoding and result decoding, making further abstraction unnecessary.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#46
File: crates/float/src/lib.rs:153-155
Timestamp: 2025-06-13T13:41:30.549Z
Learning: When generating Rust bindings for Solidity contracts in this repository, parameter names are intentionally kept identical to the Solidity ABI (e.g., using `str` even though it shadows the Rust primitive) to preserve one-to-one consistency with the contract.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#68
File: crates/float/src/lib.rs:134-135
Timestamp: 2025-06-21T11:07:19.190Z
Learning: In Alloy primitives library, B256 is a type alias for FixedBytes<32> (pub type B256 = FixedBytes<32>), making them completely interchangeable in type usage. Changing between these types is not a breaking change.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#46
File: .github/workflows/rainix.yaml:50-50
Timestamp: 2025-06-11T10:19:16.675Z
Learning: In the rain.math.float CI workflow, the `nix develop -c rainix-sol-prelude` step is required for Rust jobs as well, because Rust code uses JSON ABI artifacts generated during the Solidity prelude to drive `alloy::sol!` type generation.

src/concrete/DecimalFloat.sol (4)

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#58
File: src/concrete/DecimalFloat.sol:175-182
Timestamp: 2025-06-16T13:17:28.513Z
Learning: In the rainlanguage/rain.math.float codebase, there's an established naming convention where functions accepting a `Float` type parameter consistently use `float` as the parameter name, even though it shadows the type name. This pattern is used throughout `LibDecimalFloat.sol` and should be maintained for consistency in related contracts like `DecimalFloat.sol`.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#64
File: src/concrete/DecimalFloat.sol:0-0
Timestamp: 2025-06-17T10:02:01.394Z
Learning: In the rain.math.float project, the Float type is designed with a specific bit layout: 224-bit signed coefficient and 32-bit signed exponent, represented as 32 bytes total. The LibDecimalFloat.unpack function returns values that are guaranteed to fit within int224 and int32 ranges due to this internal representation, making explicit range checks before casting unnecessary.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#64
File: src/concrete/DecimalFloat.sol:0-0
Timestamp: 2025-06-17T10:02:01.394Z
Learning: In the rain.math.float project, the Float type is designed with a specific bit layout: 224-bit signed coefficient and 32-bit signed exponent, represented as 32 bytes total. The LibDecimalFloat.unpack function returns values that are guaranteed to fit within int224 and int32 ranges due to this internal representation, making explicit range checks before casting unnecessary.

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#30
File: test/src/lib/LibDecimalFloat.gt.t.sol:33-36
Timestamp: 2025-04-25T03:58:01.307Z
Learning: In the rain.math.float library, all values of `Float` (which is a type alias for bytes32) are considered valid and can be safely used with methods like gt(), lt(), or eq() without causing reverts.

test_js/float.test.ts (7)

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#58
File: src/concrete/DecimalFloat.sol:175-182
Timestamp: 2025-06-16T13:17:28.513Z
Learning: In the rainlanguage/rain.math.float codebase, there's an established naming convention where functions accepting a `Float` type parameter consistently use `float` as the parameter name, even though it shadows the type name. This pattern is used throughout `LibDecimalFloat.sol` and should be maintained for consistency in related contracts like `DecimalFloat.sol`.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#58
File: crates/float/src/lib.rs:382-401
Timestamp: 2025-06-16T13:19:32.009Z
Learning: In the rainlanguage/rain.math.float codebase, variable shadowing in property tests like test_lt_eq_gt_with_add is acceptable when it represents a logical progression of the same conceptual value being tested through different states.

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#30
File: test/src/lib/LibDecimalFloat.gt.t.sol:33-36
Timestamp: 2025-04-25T03:58:01.307Z
Learning: In the rain.math.float library, all values of `Float` (which is a type alias for bytes32) are considered valid and can be safely used with methods like gt(), lt(), or eq() without causing reverts.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#46
File: crates/float/proptest-regressions/lib.txt:1-3
Timestamp: 2025-06-11T09:03:20.771Z
Learning: The file `crates/float/proptest-regressions/lib.txt` is automatically generated by proptest and should not be manually edited.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#64
File: src/concrete/DecimalFloat.sol:0-0
Timestamp: 2025-06-17T10:02:01.394Z
Learning: In the rain.math.float project, the Float type is designed with a specific bit layout: 224-bit signed coefficient and 32-bit signed exponent, represented as 32 bytes total. The LibDecimalFloat.unpack function returns values that are guaranteed to fit within int224 and int32 ranges due to this internal representation, making explicit range checks before casting unnecessary.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#64
File: src/concrete/DecimalFloat.sol:0-0
Timestamp: 2025-06-17T10:02:01.394Z
Learning: In the rain.math.float project, the Float type is designed with a specific bit layout: 224-bit signed coefficient and 32-bit signed exponent, represented as 32 bytes total. The LibDecimalFloat.unpack function returns values that are guaranteed to fit within int224 and int32 ranges due to this internal representation, making explicit range checks before casting unnecessary.

Learnt from: rouzwelt
PR: rainlanguage/rain.math.float#76
File: test_js/float.test.ts:9-32
Timestamp: 2025-07-17T02:38:44.698Z
Learning: In the rainlanguage/rain.math.float repository, the user rouzwelt accepts non-null assertions in test files because tests should throw and fail immediately when something goes wrong, making it clear where the issue occurred.

crates/float/src/js_api.rs (4)

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#58
File: src/concrete/DecimalFloat.sol:175-182
Timestamp: 2025-06-16T13:17:28.513Z
Learning: In the rainlanguage/rain.math.float codebase, there's an established naming convention where functions accepting a `Float` type parameter consistently use `float` as the parameter name, even though it shadows the type name. This pattern is used throughout `LibDecimalFloat.sol` and should be maintained for consistency in related contracts like `DecimalFloat.sol`.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#57
File: crates/float/src/lib.rs:316-328
Timestamp: 2025-06-18T09:10:41.740Z
Learning: In the rain.math.float codebase, the user prefers implementing standard Rust traits (like Neg) rather than creating redundant public methods when the trait already provides the needed functionality. Float implements Copy, so reference usage with operators is not a concern.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#64
File: src/concrete/DecimalFloat.sol:0-0
Timestamp: 2025-06-17T10:02:01.394Z
Learning: In the rain.math.float project, the Float type is designed with a specific bit layout: 224-bit signed coefficient and 32-bit signed exponent, represented as 32 bytes total. The LibDecimalFloat.unpack function returns values that are guaranteed to fit within int224 and int32 ranges due to this internal representation, making explicit range checks before casting unnecessary.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#64
File: src/concrete/DecimalFloat.sol:0-0
Timestamp: 2025-06-17T10:02:01.394Z
Learning: In the rain.math.float project, the Float type is designed with a specific bit layout: 224-bit signed coefficient and 32-bit signed exponent, represented as 32 bytes total. The LibDecimalFloat.unpack function returns values that are guaranteed to fit within int224 and int32 ranges due to this internal representation, making explicit range checks before casting unnecessary.

crates/float/src/lib.rs (9)

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#58
File: src/concrete/DecimalFloat.sol:175-182
Timestamp: 2025-06-16T13:17:28.513Z
Learning: In the rainlanguage/rain.math.float codebase, there's an established naming convention where functions accepting a `Float` type parameter consistently use `float` as the parameter name, even though it shadows the type name. This pattern is used throughout `LibDecimalFloat.sol` and should be maintained for consistency in related contracts like `DecimalFloat.sol`.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#64
File: src/concrete/DecimalFloat.sol:0-0
Timestamp: 2025-06-17T10:02:01.394Z
Learning: In the rain.math.float project, the Float type is designed with a specific bit layout: 224-bit signed coefficient and 32-bit signed exponent, represented as 32 bytes total. The LibDecimalFloat.unpack function returns values that are guaranteed to fit within int224 and int32 ranges due to this internal representation, making explicit range checks before casting unnecessary.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#64
File: src/concrete/DecimalFloat.sol:0-0
Timestamp: 2025-06-17T10:02:01.394Z
Learning: In the rain.math.float project, the Float type is designed with a specific bit layout: 224-bit signed coefficient and 32-bit signed exponent, represented as 32 bytes total. The LibDecimalFloat.unpack function returns values that are guaranteed to fit within int224 and int32 ranges due to this internal representation, making explicit range checks before casting unnecessary.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#57
File: crates/float/src/lib.rs:316-328
Timestamp: 2025-06-18T09:10:41.740Z
Learning: In the rain.math.float codebase, the user prefers implementing standard Rust traits (like Neg) rather than creating redundant public methods when the trait already provides the needed functionality. Float implements Copy, so reference usage with operators is not a concern.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#58
File: crates/float/src/lib.rs:201-232
Timestamp: 2025-06-16T13:14:38.431Z
Learning: In the rain.math.float Rust crate, the `execute_call` function already provides sufficient abstraction for EVM contract calls by handling execution boilerplate, error handling, and result processing. Individual methods like `lt`, `eq`, `gt` only need to handle their specific call encoding and result decoding, making further abstraction unnecessary.

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#30
File: test/src/lib/LibDecimalFloat.gt.t.sol:33-36
Timestamp: 2025-04-25T03:58:01.307Z
Learning: In the rain.math.float library, all values of `Float` (which is a type alias for bytes32) are considered valid and can be safely used with methods like gt(), lt(), or eq() without causing reverts.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#46
File: crates/float/proptest-regressions/lib.txt:1-3
Timestamp: 2025-06-11T09:03:20.771Z
Learning: The file `crates/float/proptest-regressions/lib.txt` is automatically generated by proptest and should not be manually edited.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#59
File: crates/float/src/lib.rs:447-461
Timestamp: 2025-06-17T10:11:32.740Z
Learning: In the rainlanguage/rain.math.float repository, the user 0xgleb prefers using .unwrap() over ? in tests because it provides clearer stack traces showing the exact line where panics occurred, making debugging easier.

Learnt from: 0xgleb
PR: rainlanguage/rain.math.float#70
File: crates/float/src/evm.rs:38-43
Timestamp: 2025-07-03T11:20:50.456Z
Learning: In the rainlanguage/rain.math.float codebase, the user 0xgleb prefers not to add explanatory comments for well-established Rust idioms like the double `?` pattern, as these are self-explanatory to experienced Rust developers and don't need over-commenting.

🧬 Code Graph Analysis (1)

crates/float/src/lib.rs (1)

crates/float/src/evm.rs (1)

• execute_call (34-63)

🪛 Biome (1.9.4)

test_js/float.test.ts

[error] 32-32: Forbidden non-null assertion.

(lint/style/noNonNullAssertion)

---

[error] 33-33: Forbidden non-null assertion.

(lint/style/noNonNullAssertion)

---

[error] 39-39: Forbidden non-null assertion.

(lint/style/noNonNullAssertion)

---

[error] 40-40: Forbidden non-null assertion.

(lint/style/noNonNullAssertion)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (1)

• GitHub Check: rainix (macos-latest, rainix-rs-test)

🔇 Additional comments (6)

src/concrete/DecimalFloat.sol (1)

195-202: LGTM! Perfect consistency with established patterns.

The new toFixedDecimalLossless function follows the exact same pattern as other exposed functions in the contract, with proper documentation and consistent parameter naming using float (matching the established convention from the learnings).

crates/float/src/js_api.rs (1)

146-171: LGTM! Well-structured JavaScript API method.

The new to_fixed_decimal_js method follows the established patterns in the codebase perfectly:

• Proper documentation with clear TypeScript example
• Consistent error handling that propagates FloatError
• Appropriate conversion of U256 to string for JavaScript consumption
• Correct use of #[wasm_export] attribute

test_js/float.test.ts (1)

31-42: LGTM! Comprehensive test coverage for the new functionality.

The new test cases provide excellent coverage:

• Basic conversion test validates the core functionality
• Roundtrip test ensures consistency between fromFixedDecimal and toFixedDecimal
• Both tests follow the established patterns in the test suite

The non-null assertions are acceptable in test contexts as they help identify issues quickly when they occur.

crates/float/src/lib.rs (3)

82-115: LGTM! Excellent implementation following established patterns.

The new to_fixed_decimal method is perfectly implemented:

• Follows the exact same pattern as other EVM call methods in the file
• Uses execute_call with proper error handling and ABI encoding/decoding
• Comprehensive documentation with clear example
• Proper return type Result<U256, FloatError>

The implementation is consistent with the existing codebase architecture and error handling patterns.

---

1342-1358: LGTM! Comprehensive test coverage for the new functionality.

The test cases provide excellent coverage of various scenarios:

• Zero values with different decimal places
• Small and large numbers
• Edge cases like 1e-18 with 18 decimals
• Different decimal precision levels

Each test case properly validates the conversion by comparing with expected U256 values.

---

1397-1409: LGTM! Excellent addition of roundtrip testing.

The enhancement of the property test to include roundtrip verification is excellent:

• Renamed appropriately to reflect the extended functionality
• Added verification that to_fixed_decimal returns the original value
• This ensures the conversion is truly lossless as intended

The roundtrip property test is a valuable addition that strengthens the test suite by ensuring both directions of conversion work correctly together.

✨ Finishing Touches

• 📝 Generate Docstrings

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