likewise/CLAUDE.md

Likewise - Floating Point Diff Implementation

Codebase Structure

src/
├── lib.rs              # Main entry, re-exports
├── types.rs            # DiffOp, Change, ChangeTag, Algorithm enums
├── common.rs           # capture_diff_slices(), get_diff_ratio()
├── algorithms/         # myers.rs, patience.rs, lcs.rs, hook.rs, utils.rs
├── text/              # TextDiff, DiffableStr trait
├── udiff.rs           # Unified diff output
└── utils.rs           # Text utilities

Current Diff Flow

1. capture_diff_slices(alg, &old, &new) → Vec<DiffOp>
2. DiffOp::iter_changes(&old, &new) → Iterator<Change<T>>
3. Requires T: Hash + Eq + Ord

Key Types

pub enum DiffOp {
    Equal { old_index: usize, new_index: usize, len: usize },
    Delete { old_index: usize, old_len: usize, new_index: usize },
    Insert { old_index: usize, new_index: usize, new_len: usize },
    Replace { old_index: usize, old_len: usize, new_index: usize, new_len: usize },
}

pub struct Change<T> {
    pub(crate) tag: ChangeTag,
    pub(crate) old_index: Option<usize>,
    pub(crate) new_index: Option<usize>, 
    pub(crate) value: T,
}

Algorithm Trait

pub trait DiffHook {
    type Error;
    fn equal(&mut self, old: usize, new: usize, len: usize) -> Result<(), Self::Error>;
    fn delete(&mut self, old: usize, old_len: usize, new: usize) -> Result<(), Self::Error>;
    fn insert(&mut self, old: usize, new: usize, new_len: usize) -> Result<(), Self::Error>;
    fn replace(&mut self, old: usize, old_len: usize, new: usize, new_len: usize) -> Result<(), Self::Error>;
}

Task: FP Comparison

Add eps/ulps floating point comparison for f32/f64 slices.

Implementation Points

1. New comparison trait alongside existing PartialEq requirement
2. Algorithm modification to use FP-aware comparison in core loops
3. API surface for specifying epsilon/ulps parameters
4. Testing edge cases: NaN, infinity, subnormals, precision boundaries

Files to Modify

• src/algorithms/myers.rs - Core comparison logic
• src/algorithms/patience.rs - Core comparison logic
• src/algorithms/lcs.rs - Core comparison logic
• src/common.rs - Add FP-aware capture_diff_slices_fp()
• examples/floating_point.rs - Usage demonstration

Example Usage Goal

let old = vec![1.0, 2.0, 3.0];
let new = vec![1.000001, 2.0, 3.1];

// Absolute epsilon
let ops = capture_diff_slices_fp_eps(Algorithm::Myers, &old, &new, 0.0001);

// Relative ulps  
let ops = capture_diff_slices_fp_ulps(Algorithm::Myers, &old, &new, 4);

Testing Strategy

Use existing insta snapshot testing framework. Test matrices:

• Normal values with various epsilon/ulps settings
• Edge cases: ±0.0, NaN, ±infinity
• Precision boundaries and subnormal values
• Mixed normal/edge case arrays

Status

• CI fixed (Rust 1.66 MSRV)
• Codebase analysis complete
• Design FP comparison API
• Implement core FP comparison logic
• Add comprehensive tests
• Create usage examples