solana/bucket_map/src/index_entry.rs

use crate::bucket::Bucket;
use crate::bucket_storage::{BucketStorage, Uid};
use crate::RefCount;
use solana_sdk::clock::Slot;
use solana_sdk::pubkey::Pubkey;
use std::collections::hash_map::DefaultHasher;
use std::fmt::Debug;
use std::hash::{Hash, Hasher};

#[repr(C)]
#[derive(Debug, Copy, Clone, PartialEq)]
// one instance of this per item in the index
// stored in the index bucket
pub struct IndexEntry {
    pub key: Pubkey, // can this be smaller if we have reduced the keys into buckets already?
    pub ref_count: RefCount, // can this be smaller? Do we ever need more than 4B refcounts?
    pub storage_offset: u64, // smaller? since these are variably sized, this could get tricky. well, actually accountinfo is not variable sized...
    // if the bucket doubled, the index can be recomputed using create_bucket_capacity_pow2
    pub storage_capacity_when_created_pow2: u8, // see data_location
    pub num_slots: Slot, // can this be smaller? epoch size should ~ be the max len. this is the num elements in the slot list
}

impl IndexEntry {
    pub fn data_bucket_from_num_slots(num_slots: Slot) -> u64 {
        (num_slots as f64).log2().ceil() as u64 // use int log here?
    }

    pub fn data_bucket_ix(&self) -> u64 {
        Self::data_bucket_from_num_slots(self.num_slots)
    }

    pub fn ref_count(&self) -> RefCount {
        self.ref_count
    }

    // This function maps the original data location into an index in the current bucket storage.
    // This is coupled with how we resize bucket storages.
    pub fn data_loc(&self, storage: &BucketStorage) -> u64 {
        self.storage_offset << (storage.capacity_pow2 - self.storage_capacity_when_created_pow2)
    }

    pub fn read_value<'a, T>(&self, bucket: &'a Bucket<T>) -> Option<(&'a [T], RefCount)> {
        let data_bucket_ix = self.data_bucket_ix();
        let data_bucket = &bucket.data[data_bucket_ix as usize];
        let slice = if self.num_slots > 0 {
            let loc = self.data_loc(data_bucket);
            let uid = Self::key_uid(&self.key);
            assert_eq!(uid, bucket.data[data_bucket_ix as usize].uid(loc));
            bucket.data[data_bucket_ix as usize].get_cell_slice(loc, self.num_slots)
        } else {
            // num_slots is 0. This means we don't have an actual allocation.
            // can we trust that the data_bucket is even safe?
            bucket.data[data_bucket_ix as usize].get_empty_cell_slice()
        };
        Some((slice, self.ref_count))
    }
    pub fn key_uid(key: &Pubkey) -> Uid {
        let mut s = DefaultHasher::new();
        key.hash(&mut s);
        s.finish().max(1u64)
    }
}