From c57649e7586906c74beef943a51d2103bae9e5c7 Mon Sep 17 00:00:00 2001
From: magical <magical@tilde.town>
Date: Sun, 23 Jan 2022 01:25:42 +0000
Subject: [PATCH] stop hardcoding the hash function

---
 pmap.go      | 26 +++++++++++---------------
 pmap_test.go | 13 ++++++++++---
 2 files changed, 21 insertions(+), 18 deletions(-)

diff --git a/pmap.go b/pmap.go
index d0a5e66..3785b9e 100644
--- a/pmap.go
+++ b/pmap.go
@@ -43,8 +43,13 @@ type leaf struct {
 	v Value
 }
 
-func New() Map {
-	return pmap{}
+type HashFunc = func(Key) uint32
+
+func New(hash HashFunc) Map {
+	if hash == nil {
+		panic("pmap.New: nil hash")
+	}
+	return pmap{hash: hash}
 }
 
 func (p pmap) Len() int {
@@ -52,13 +57,13 @@ func (p pmap) Len() int {
 }
 
 func (p pmap) Get(k Key) (Value, bool) {
-	var zero Key
-	h := hash(k) // TODO: p.hash
+	var zero Value
+	h := p.hash(k)
 	return lookup(p.root, 0, h, k, zero)
 }
 
 func (p pmap) Set(k Key, v Value) Map {
-	h := hash(k) // TODO: p.hash
+	h := p.hash(k)
 	root, added := insert(p.root, 0, h, k, v, hash)
 	p.root = root
 	if added {
@@ -72,13 +77,6 @@ func (p pmap) Del(k Key) Map {
 	return p
 }
 
-func hash(k Key) uint32 {
-	//u := uint(k.(int))*6364136223846793005 + 1
-	//return uint32(u >> 32)
-	u := uint(k.(int))
-	return uint32(u + u>>32)
-}
-
 func (m *node) getNode(shift, hash uint32, key Key) interface{} {
 	i := hash >> shift & nodeMask
 	return m.child[i]
@@ -131,9 +129,7 @@ func newnode(child interface{}, hash, shift uint32) *node {
 	return n
 }
 
-type hashFunc = func(Key) uint32
-
-func insert(n interface{}, shift, hash uint32, key Key, val Value, hashFn hashFunc) (newNode interface{}, added bool) {
+func insert(n interface{}, shift, hash uint32, key Key, val Value, hashFn HashFunc) (newNode interface{}, added bool) {
 	if n == nil {
 		return leaf{key, val}, true
 	}
diff --git a/pmap_test.go b/pmap_test.go
index 3916a27..868ca7a 100644
--- a/pmap_test.go
+++ b/pmap_test.go
@@ -5,8 +5,15 @@ import (
 	"testing"
 )
 
+func hash(k Key) uint32 {
+	//u := uint(k.(int))*6364136223846793005 + 1
+	//return uint32(u >> 32)
+	u := uint(k.(int))
+	return uint32(u + u>>32)
+}
+
 func TestPmap(t *testing.T) {
-	p := New()
+	p := New(hash)
 	const numElems = 100
 	for i := range iter(numElems) {
 		p = p.Set(i, i)
@@ -38,7 +45,7 @@ func BenchmarkGetAbsent(b *testing.B) {
 }
 
 func benchmarkGet(b *testing.B, numElems int) {
-	p := New()
+	p := New(hash)
 	for i := range iter(numElems) {
 		p = p.Set(i, i)
 	}
@@ -60,7 +67,7 @@ func benchmarkGet(b *testing.B, numElems int) {
 }
 
 func benchmarkGetAbsent(b *testing.B, numElems int) {
-	p := New()
+	p := New(hash)
 	for i := range iter(numElems) {
 		p = p.Set(-i-1, i)
 	}