Memorize hash

[zhangsoledad]

• Cache hashes in the source structs (Header and Transaction) since they are constructed.
• Do not calculate Header hash when fetching header from database.
• Optimize ProposalShortId::hash().
• Save hashes related to Transaction into database.
  So, we can just fetch them from database instead of compute them.

[yangby-cryptape]

Summary

I think, only Header and Transaction are worth memorizing (I did).

All others can be found be a shell command:

yangby@laptop:ckb> grep -r 'fn [a-z_]*hash(' [^t]* | grep "[-]> [^&]*H256"
core/src/header.rs:    pub fn pow_hash(&self) -> H256 {
core/src/header.rs:    pub fn pow_hash(&self) -> H256 {
core/src/script.rs:    pub fn hash(&self) -> H256 {
core/src/block.rs:    pub fn cal_uncles_hash(&self) -> H256 {
core/src/uncle.rs:pub fn uncles_hash(uncles: &[UncleBlock]) -> H256 {
core/src/transaction.rs:    pub fn data_hash(&self) -> H256 {
core/src/transaction.rs:    pub fn hash(&self) -> H256 {
rpc/src/module/chain.rs:    fn get_block_hash(&self, _number: String) -> Result<Option<H256>>;
rpc/src/module/chain.rs:    fn get_block_hash(&self, number: String) -> Result<Option<H256>> {
shared/src/shared.rs:    fn block_hash(&self, number: BlockNumber) -> Option<H256> {
store/src/store.rs:    fn get_block_hash(&self, number: BlockNumber) -> Option<H256>;
store/src/store.rs:    fn get_block_hash(&self, number: BlockNumber) -> Option<H256> {
sync/src/types.rs:    pub fn block_hash(&self, number: BlockNumber) -> Option<H256> {
verification/src/tests/dummy.rs:    fn block_hash(&self, _height: u64) -> Option<H256> {

Further

I think we can optimize the hash of ProposalShortId.

ckb/core/src/transaction.rs

Lines 408 to 409 in de1cfc9

	#[derive(Serialize, Deserialize, Copy, Clone, PartialEq, Eq, Default, Hash)]
	pub struct ProposalShortId([u8; 10]);

ckb/core/src/transaction.rs

Lines 457 to 459 in de1cfc9

	pub fn hash(&self) -> H256 {
	blake2b_256(serialize(self).expect("ProposalShortId serialize should not fail")).into()
	}

ckb/core/src/block.rs

Lines 90 to 98 in de1cfc9

	pub fn cal_proposals_root(&self) -> H256 {
	merkle_root(
	&self
	.proposals
	.iter()
	.map(ProposalShortId::hash)
	.collect::<Vec<_>>(),
	)
	}

ckb/core/src/uncle.rs

Lines 43 to 51 in de1cfc9

	pub fn cal_proposals_root(&self) -> H256 {
	merkle_root(
	&self
	.proposals
	.iter()
	.map(ProposalShortId::hash)
	.collect::<Vec<_>>(),
	)
	}

My suggest is:

pub fn hash(&self) -> H256 {
    let mut h = H256::zero();
    h.as_bytes_mut()[..self.0.len()].copy_from_slice(&self.0[..]);
    h
}

[TheWaWaR]

Add assert_debug! in from_bytes_with_hash to check hash consistent with the header.