keys.go

package sroar

import (
	"fmt"
	"strings"
)

var (
	indexNodeSize  = 0
	indexNumKeys   = 1
	indexNodeStart = 2
)

// node stores uint64 keys and the corresponding container offset in the buffer.
// 0th index (indexNodeSize) is used for storing the size of node in bytes.
// 1st index (indexNumKeys) is used for storing the number of keys.
// 2nd index is where we start writing the key-value pairs.
type node []uint64

func keyOffset(i int) int { return indexNodeStart + 2*i }
func valOffset(i int) int { return indexNodeStart + 2*i + 1 }

func (n node) numKeys() int        { return int(n[indexNumKeys]) }
func (n node) size() int           { return int(n[indexNodeSize]) }
func (n node) maxKeys() int        { return (len(n) - indexNodeStart) / 2 }
func (n node) key(i int) uint64    { return n[keyOffset(i)] }
func (n node) val(i int) uint64    { return n[valOffset(i)] }
func (n node) data(i int) []uint64 { return n[keyOffset(i):keyOffset(i+1)] }

func (n node) uint64(idx int) uint64   { return n[idx] }
func (n node) setAt(idx int, k uint64) { n[idx] = k }

func (n node) setNumKeys(num int) { n[indexNumKeys] = uint64(num) }
func (n node) setNodeSize(sz int) { n[indexNodeSize] = uint64(sz) }

func (n node) maxKey() uint64 {
	idx := n.numKeys()
	// numKeys == index of the max key, because 0th index is being used for meta information.
	if idx == 0 {
		return 0
	}
	return n.key(idx)
}

func (n node) moveRight(lo int) {
	hi := n.numKeys()
	assert(!n.isFull())
	// copy works despite of overlap in src and dst.
	// See https://golang.org/pkg/builtin/#copy
	copy(n[keyOffset(lo+1):keyOffset(hi+1)], n[keyOffset(lo):keyOffset(hi)])
}

// isFull checks that the node is already full.
func (n node) isFull() bool {
	return n.numKeys() == n.maxKeys()
}

// Search returns the index of a smallest key >= k in a node.
func (n node) search(k uint64) int {
	N := n.numKeys()
	lo, hi := 0, N-1
	for lo+16 <= hi {
		mid := lo + (hi-lo)/2
		ki := n.key(mid)
		// fmt.Printf("lo: %d mid: %d hi: %d. ki: %#x k: %#x\n", lo, mid, hi, ki, k)

		if ki < k {
			lo = mid + 1
		} else if ki > k {
			hi = mid
			// We should keep it equal, and not -1, because we'll take the first greater entry.
		} else {
			// fmt.Printf("returning mid: %d\n", mid)
			return mid
		}
	}
	for ; lo <= hi; lo++ {
		ki := n.key(lo)
		// fmt.Printf("itr. lo: %d hi: %d. ki: %#x k: %#x\n", lo, hi, ki, k)
		if ki >= k {
			return lo
		}
	}
	return N
	// if N < 4 {
	// simd.Search has a bug which causes this to return index 11 when it should be returning index
	// 9.
	// }
	// return int(simd.Search(n[keyOffset(0):keyOffset(N)], k))
}

func zeroOut(data []uint64) {
	for i := 0; i < len(data); i++ {
		data[i] = 0
	}
}

// compacts the node i.e., remove all the kvs with value < lo. It returns the remaining number of
// keys.
func (n node) compact(lo uint64) int {
	N := n.numKeys()
	mk := n.maxKey()
	var left, right int
	for right = 0; right < N; right++ {
		if n.val(right) < lo && n.key(right) < mk {
			// Skip over this key. Don't copy it.
			continue
		}
		// Valid data. Copy it from right to left. Advance left.
		if left != right {
			copy(n.data(left), n.data(right))
		}
		left++
	}
	// zero out rest of the kv pairs.
	zeroOut(n[keyOffset(left):keyOffset(right)])
	n.setNumKeys(left)

	// If the only key we have is the max key, and its value is less than lo, then we can indicate
	// to the caller by returning a zero that it's OK to drop the node.
	if left == 1 && n.key(0) == mk && n.val(0) < lo {
		return 0
	}
	return left
}

// getValue returns the value corresponding to the key if found.
func (n node) getValue(k uint64) (uint64, bool) {
	k &= mask // Ensure k has its lowest bits unset.
	idx := n.search(k)
	// key is not found
	if idx >= n.numKeys() {
		return 0, false
	}
	if ki := n.key(idx); ki == k {
		return n.val(idx), true
	}
	return 0, false
}

// set returns true if it added a new key.
func (n node) set(k, v uint64) bool {
	N := n.numKeys()
	idx := n.search(k)
	if idx == N {
		n.setNumKeys(N + 1)
		n.setAt(keyOffset(idx), k)
		n.setAt(valOffset(idx), v)
		return true
	}

	ki := n.key(idx)
	if N == n.maxKeys() {
		// This happens during split of non-root node, when we are updating the child pointer of
		// right node. Hence, the key should already exist.
		assert(ki == k)
	}
	if ki == k {
		n.setAt(valOffset(idx), v)
		return false
	}
	assert(ki > k)
	// Found the first entry which is greater than k. So, we need to fit k
	// just before it. For that, we should move the rest of the data in the
	// node to the right to make space for k.
	n.moveRight(idx)
	n.setNumKeys(N + 1)
	n.setAt(keyOffset(idx), k)
	n.setAt(valOffset(idx), v)
	return true
	// panic("shouldn't reach here")
}

func (n node) updateOffsets(beyond, by uint64, add bool) {
	for i := 0; i < n.numKeys(); i++ {
		if offset := n.val(i); offset > beyond {
			if add {
				n.setAt(valOffset(i), offset+by)
			} else {
				assert(offset >= by)
				n.setAt(valOffset(i), offset-by)
			}
		}
	}
}

func (n node) iterate(fn func(node, int)) {
	for i := 0; i < n.maxKeys(); i++ {
		if k := n.key(i); k > 0 {
			fn(n, i)
		} else {
			break
		}
	}
}

func (n node) print(parentID uint64) {
	var keys []string
	n.iterate(func(n node, i int) {
		keys = append(keys, fmt.Sprintf("%d", n.key(i)))
	})
	if len(keys) > 8 {
		copy(keys[4:], keys[len(keys)-4:])
		keys[3] = "..."
		keys = keys[:8]
	}
	fmt.Printf("num keys: %d keys: %s\n", n.numKeys(), strings.Join(keys, " "))
}