Function reth_trie::encode_path_leaf

pub fn encode_path_leaf(nibbles: &Nibbles, is_leaf: bool) -> SmallVec<[u8; 36]>

Encodes a given path leaf as a compact array of bytes.

In resulted array, each byte represents two “nibbles” (half-bytes or 4 bits) of the original hex data, along with additional information about the leaf itself.

The method takes the following input: is_leaf: A boolean value indicating whether the current node is a leaf node or not.

The first byte of the encoded vector is set based on the is_leaf flag and the parity of the hex data length (even or odd number of nibbles).

• If the node is an extension with even length, the header byte is 0x00.
• If the node is an extension with odd length, the header byte is 0x10 + <first nibble>.
• If the node is a leaf with even length, the header byte is 0x20.
• If the node is a leaf with odd length, the header byte is 0x30 + <first nibble>.

If there is an odd number of nibbles, store the first nibble in the lower 4 bits of the first byte of encoded.

Returns

A vector containing the compact byte representation of the nibble sequence, including the header byte.

This vector’s length is self.len() / 2 + 1. For stack-allocated nibbles, this is at most 33 bytes, so 36 was chosen as the stack capacity to round up to the next usize-aligned size.

Examples

// Extension node with an even path length:
let nibbles = Nibbles::from_nibbles(&[0x0A, 0x0B, 0x0C, 0x0D]);
assert_eq!(nibbles.encode_path_leaf(false)[..], [0x00, 0xAB, 0xCD]);

// Extension node with an odd path length:
let nibbles = Nibbles::from_nibbles(&[0x0A, 0x0B, 0x0C]);
assert_eq!(nibbles.encode_path_leaf(false)[..], [0x1A, 0xBC]);

// Leaf node with an even path length:
let nibbles = Nibbles::from_nibbles(&[0x0A, 0x0B, 0x0C, 0x0D]);
assert_eq!(nibbles.encode_path_leaf(true)[..], [0x20, 0xAB, 0xCD]);

// Leaf node with an odd path length:
let nibbles = Nibbles::from_nibbles(&[0x0A, 0x0B, 0x0C]);
assert_eq!(nibbles.encode_path_leaf(true)[..], [0x3A, 0xBC]);