From 30ea17e8a481a5488073da4c0bb6c3838f2309c5 Mon Sep 17 00:00:00 2001
From: Patrick Crosby <pcrosby@gmail.com>
Date: Thu, 19 Sep 2019 23:12:45 -0500
Subject: [PATCH] Add option to use FNV32a hash (UseFnv)

---
 consistent.go      | 15 ++++++++++++++
 consistent_test.go | 50 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/consistent.go b/consistent.go
index 4a9e148..a1a1fa0 100644
--- a/consistent.go
+++ b/consistent.go
@@ -23,6 +23,7 @@ package consistent // import "stathat.com/c/consistent"
 import (
 	"errors"
 	"hash/crc32"
+	"hash/fnv"
 	"sort"
 	"strconv"
 	"sync"
@@ -50,6 +51,7 @@ type Consistent struct {
 	NumberOfReplicas int
 	count            int64
 	scratch          [64]byte
+	UseFnv           bool
 	sync.RWMutex
 }
 
@@ -236,6 +238,13 @@ func (c *Consistent) GetN(name string, n int) ([]string, error) {
 }
 
 func (c *Consistent) hashKey(key string) uint32 {
+	if c.UseFnv {
+		return c.hashKeyFnv(key)
+	}
+	return c.hashKeyCRC32(key)
+}
+
+func (c *Consistent) hashKeyCRC32(key string) uint32 {
 	if len(key) < 64 {
 		var scratch [64]byte
 		copy(scratch[:], key)
@@ -244,6 +253,12 @@ func (c *Consistent) hashKey(key string) uint32 {
 	return crc32.ChecksumIEEE([]byte(key))
 }
 
+func (c *Consistent) hashKeyFnv(key string) uint32 {
+	h := fnv.New32a()
+	h.Write([]byte(key))
+	return h.Sum32()
+}
+
 func (c *Consistent) updateSortedHashes() {
 	hashes := c.sortedHashes[:0]
 	//reallocate if we're holding on to too much (1/4th)
diff --git a/consistent_test.go b/consistent_test.go
index f566468..7f29e17 100644
--- a/consistent_test.go
+++ b/consistent_test.go
@@ -6,6 +6,7 @@ package consistent
 
 import (
 	"bufio"
+	"encoding/base64"
 	"math/rand"
 	"os"
 	"runtime"
@@ -740,3 +741,52 @@ func TestConcurrentGetSet(t *testing.T) {
 	}
 	wg.Wait()
 }
+
+func TestDistributionFnv(t *testing.T) {
+	x := New()
+	x.UseFnv = true
+	x.Add("abcdefg")
+	x.Add("hijklmn")
+	x.Add("opqrstu")
+	dist := make(map[string]int)
+	g := make([]byte, 12)
+	for i := 0; i < 10000; i++ {
+		_, err := rand.Read(g)
+		if err != nil {
+			t.Fatal(err)
+		}
+		s := base64.StdEncoding.EncodeToString(g)
+		r, err := x.Get(s)
+		if err != nil {
+			t.Fatal(err)
+		}
+		dist[r] = dist[r] + 1
+	}
+	for k, v := range dist {
+		t.Logf("%s: %d", k, v)
+	}
+}
+
+func TestDistributionCRC(t *testing.T) {
+	x := New()
+	x.Add("abcdefg")
+	x.Add("hijklmn")
+	x.Add("opqrstu")
+	dist := make(map[string]int)
+	g := make([]byte, 12)
+	for i := 0; i < 10000; i++ {
+		_, err := rand.Read(g)
+		if err != nil {
+			t.Fatal(err)
+		}
+		s := base64.StdEncoding.EncodeToString(g)
+		r, err := x.Get(s)
+		if err != nil {
+			t.Fatal(err)
+		}
+		dist[r] = dist[r] + 1
+	}
+	for k, v := range dist {
+		t.Logf("%s: %d", k, v)
+	}
+}