Replace math/rand with crypto/rand in cuckoo (#62)

* Seed math/rand with crypto/rand for performance

Co-authored-by: Jaskaran Veer Singh <[email protected]>

internal/cuckoo/cuckoo.go

@@ -2,6 +2,8 @@ package cuckoo
 
 import (
  "bytes"
+ crand "crypto/rand"
+ "encoding/binary"
  "fmt"
  "math/rand"
 
@@ -79,10 +81,23 @@ type Cuckoo struct {
 }
 
 // NewCuckoo instantiates a Cuckoo struct with a bucket of size Factor * size,
-// and a CuckooHasher for the 3-way cuckoo hashing.
+// seeds math/rand with a random seed, returns a CuckooHasher for the 3-way
+// cuckoo hashing.
 func NewCuckoo(size uint64, seeds [Nhash][]byte) *Cuckoo {
  cuckooHasher := NewCuckooHasher(size, seeds)
 
+ // get randombyte from crypto/rand
+ var rb [8]byte
+ if _, err := crand.Read(rb[:]); err != nil {
+ panic(err)
+ }
+
+ // WARNING: math/rand is not concurrency-safe
+ // replace with crypto/rand if that's what you want
+
+ // seed math/rand with crypto/rand
+ rand.Seed(int64(binary.LittleEndian.Uint64(rb[:])))
+
  return &Cuckoo{
  // extra element is "keeper" to which the bucketLookup can be directed
  // when there is no element present in the bucket.
@@ -181,7 +196,8 @@ func (c *Cuckoo) tryAdd(idx uint64, bucketIndices [Nhash]uint64, ignore bool, ex
 func (c *Cuckoo) tryGreedyAdd(idx uint64, bucketIndices [Nhash]uint64) (homeLessItem uint64, added bool) {
  for i := 1; i < ReInsertLimit; i++ {
  // select a random slot to be evicted
- evictedHIdx := rand.Int31n(Nhash)
+ // replace me with crypto/rand for concurrent safety
+ evictedHIdx := rand.Intn(Nhash)
  evictedBIdx := bucketIndices[evictedHIdx]
  evictedIdx := c.bucketLookup[evictedBIdx]
  // insert the item in the evicted slot