From 2af7318239c59555869d018bc355fe0e21d900c6 Mon Sep 17 00:00:00 2001
From: Nikias Bassen
Date: Thu, 12 May 2016 02:32:55 +0200
Subject: bplist: Speed up plist_to_bin conversion for large plists

Using a better hashing algorithm and a larger hash table the conversion
is A LOT faster when processing large plists. Thanks to Xiao Deng for
reporting this issue and suggesting a fix.
---
 src/bplist.c    | 11 +++++++----
 src/hashtable.c |  8 ++++----
 src/hashtable.h |  2 +-
 3 files changed, 12 insertions(+), 9 deletions(-)

(limited to 'src')

diff --git a/src/bplist.c b/src/bplist.c
index 3ba46a2..bb73b31 100644
--- a/src/bplist.c
+++ b/src/bplist.c
@@ -735,7 +735,7 @@ static unsigned int plist_data_hash(const void* key)
     case PLIST_KEY:
     case PLIST_STRING:
         buff = data->strval;
-        size = strlen(buff);
+        size = data->length;
         break;
     case PLIST_DATA:
     case PLIST_ARRAY:
@@ -752,9 +752,12 @@ static unsigned int plist_data_hash(const void* key)
         break;
     }
 
-    //now perform hash
-    for (i = 0; i < size; buff++, i++)
-        hash = hash << 7 ^ (*buff);
+    // now perform hash using djb2 hashing algorithm
+    // see: http://www.cse.yorku.ca/~oz/hash.html
+    hash += 5381;
+    for (i = 0; i < size; buff++, i++) {
+        hash = ((hash << 5) + hash) + *buff;
+    }
 
     return hash;
 }
diff --git a/src/hashtable.c b/src/hashtable.c
index 08ff934..3568f3c 100644
--- a/src/hashtable.c
+++ b/src/hashtable.c
@@ -24,7 +24,7 @@ hashtable_t* hash_table_new(hash_func_t hash_func, compare_func_t compare_func)
 {
 	hashtable_t* ht = (hashtable_t*)malloc(sizeof(hashtable_t));
 	int i;
-	for (i = 0; i < 256; i++) {
+	for (i = 0; i < 4096; i++) {
 		ht->entries[i] = NULL;
 	}
 	ht->count = 0;
@@ -38,7 +38,7 @@ void hash_table_destroy(hashtable_t *ht)
 	if (!ht) return;
 
 	int i = 0;
-	for (i = 0; i < 256; i++) {
+	for (i = 0; i < 4096; i++) {
 		if (ht->entries[i]) {
 			hashentry_t* e = ht->entries[i];
 			while (e) {
@@ -58,7 +58,7 @@ void hash_table_insert(hashtable_t* ht, void *key, void *value)
 
 	unsigned int hash = ht->hash_func(key);
 
-	int idx0 = hash & 0xFF;
+	int idx0 = hash & 0xFFF;
 
 	// get the idx0 list
 	hashentry_t* e = ht->entries[idx0];
@@ -93,7 +93,7 @@ void* hash_table_lookup(hashtable_t* ht, void *key)
 	if (!ht || !key) return NULL;
 	unsigned int hash = ht->hash_func(key);
 
-	int idx0 = hash & 0xFF;
+	int idx0 = hash & 0xFFF;
 
 	hashentry_t* e = ht->entries[idx0];
 	while (e) {
diff --git a/src/hashtable.h b/src/hashtable.h
index c28de91..60a40ab 100644
--- a/src/hashtable.h
+++ b/src/hashtable.h
@@ -32,7 +32,7 @@ typedef unsigned int(*hash_func_t)(const void* key);
 typedef int (*compare_func_t)(const void *a, const void *b);
 
 typedef struct hashtable_t {
-	hashentry_t *entries[256];
+	hashentry_t *entries[4096];
 	size_t count;
 	hash_func_t hash_func;
 	compare_func_t compare_func;
-- 
cgit v1.1-32-gdbae