# Han (weihan) - Update 8

## Summary
I had completed most of the required codes related to leaf node which includes the addition of new state epoch metadata and new Verkle proof format.

## Development
I've finished most of the development related to state epoch metadata and leaf node modification. I'm almost done with modifying the Verkle proof component.

Check out my development branch [here](https://github.com/weiihann/go-verkle/tree/state-expiry-tree).

## Code Notes
Navigating through the Verkle commitment seemed daunting at first, but it wasn't so bad when I got hands on. The following is the notes for the `NewLeafNode` function in the *tree.go* file:

1. Load Lagrange Precompile file

cfg := GetConfig()

2. For the first 128 values, build the polynomial for C1

var c1poly [NodeWidth]Fr
var c1 *Point

count, err := fillSuffixTreePoly(c1poly[:], values[:NodeWidth/2])

3. Create the commitment for C1

c1 = cfg.CommitToPoly(c1poly[:], NodeWidth-count)

4. For the last 128 values, build the polynomial for C2

var c2poly [NodeWidth]Fr
count, err = fillSuffixTreePoly(c2poly[:], values[NodeWidth/2:])

5. Create the commitment for C2

c2 := cfg.CommitToPoly(c2poly[:], NodeWidth-count)

6. Create the commitment of leaf node. First step is to get the stem (31 bytes). Then it sets the first position of polynomial to 1 (this is constant). Then, it sets the second position of the polynomial to the stem. Then, it sets the position of 2 and 3 to c1 and c2. This is consistent with the commitment formula C(1, Stem, C1, C2).

// Root commitment preparation for calculation.
stem = stem[:StemSize] // enforce a 31-byte length
var poly [NodeWidth]Fr
poly[0].SetUint64(1)
if err := StemFromBytes(&poly[1], stem); err != nil {
	return nil, err
}
banderwagon.BatchMapToScalarField([]*Fr{&poly[2], &poly[3]}, []*Point{c1, c2})

7. Build LeafNode object and return it. It will create the commitment of the node using the polynomial constructed. At this point, poly[0:5] = [1, Stem, C1, C2]. But do take note that the polynomial has a length of 256, so the rest of the elements are zero (which I assume is to be ignored).

return &LeafNode{
		// depth will be 0, but the commitment calculation
		// does not need it, and so it won't be free.
		values:     values,
		stem:       stem,
		commitment: cfg.CommitToPoly(poly[:], NodeWidth-4),
		c1:         c1,
		c2:         c2,
	}, nil
}

The rest of the functions follow a similar pattern on creating and updating the node commitment.

## Daily Updates
To ensure consistency, I post daily updates (on weekdays) on what I did for EPF. Check out my daily updates this week:

[Monday](https://twitter.com/ngweihan_eth/status/1698726060752540089)
Tuesday (skipped)
[Wednesday](https://twitter.com/ngweihan_eth/status/1699447177259688016)
Thursday (skipped)
Friday (skipped)

## Next week's Action Items
- Complete the Verkle proof component
- Complete unit testing for verkle tree modification
- Present project during EPF office hours