From f4c00fc9798d5089f7d22054a45f645cd1a0936c Mon Sep 17 00:00:00 2001
From: Joshua Haberman <joshua@reverberate.org>
Date: Sun, 14 Jun 2009 12:30:27 -0700
Subject: More work on the table implementation.

It currently beats std::map and std::hash_map by >10x.
---
 upb_table.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 46 insertions(+), 12 deletions(-)

(limited to 'upb_table.c')

diff --git a/upb_table.c b/upb_table.c
index 656da24..d28e079 100644
--- a/upb_table.c
+++ b/upb_table.c
@@ -6,7 +6,9 @@
 
 #include "upb_table.h"
 
+#include <assert.h>
 #include <stdlib.h>
+#include <string.h>
 
 static int compare_entries(const void *f1, const void *f2)
 {
@@ -26,6 +28,18 @@ static uint32_t round_up_to_pow2(uint32_t v)
   return v;
 }
 
+static struct upb_inttable_entry *find_empty_slot(struct upb_inttable *table)
+{
+  /* TODO: does it matter that this is biased towards the front of the table? */
+  for(uint32_t i = 0; i < table->size; i++) {
+    struct upb_inttable_entry *e =
+        upb_inttable_entry_get(table->entries, i, table->entry_size);
+    if(e->key == UPB_EMPTY_ENTRY) return e;
+  }
+  assert(false);
+  return NULL;
+}
+
 void upb_inttable_init(struct upb_inttable *table, void *entries,
                        int num_entries, int entry_size)
 {
@@ -53,31 +67,51 @@ void upb_inttable_init(struct upb_inttable *table, void *entries,
   uint32_t min_size_by_load = all_in_array ? n : (double)num_entries / 0.85;
   uint32_t min_size = max(n, min_size_by_load);
   table->size = round_up_to_pow2(min_size);
-
+  table->entry_size = entry_size;
   table->entries = malloc(table->size * entry_size);
+
   /* Initialize to empty. */
   for(size_t i = 0; i < table->size; i++) {
-    struct upb_inttable_entry *e = upb_inttable_get(table, i, entry_size);
-    e->key = UPB_END_OF_CHAIN;
-    e->next = UPB_END_OF_CHAIN;
+    struct upb_inttable_entry *e =
+        upb_inttable_entry_get(table->entries, i, entry_size);
+    e->key = UPB_EMPTY_ENTRY;
+    e->next = NULL;
   }
 
   /* Insert the elements. */
   for(int i = 0; i < num_entries; i++) {
-    struct upb_inttable_entry *e =
-        upb_inttable_entry_get(entries, i, entry_size);
-    int32_t hash = upb_inttable_hash(table, e->key);
-    struct upb_inttable_entry *table_e =
-        upb_inttable_get(table, hash, entry_size);
-    if(table_e->key != UPB_END_OF_CHAIN) {  /* Collision. */
-      if(hash == upb_inttable_hash(table, table_e->key)) {
+    struct upb_inttable_entry *e, *table_e;
+    e = upb_inttable_entry_get(entries, i, entry_size);
+    table_e = upb_inttable_mainpos(table, e->key);
+    if(table_e->key != UPB_EMPTY_ENTRY) {  /* Collision. */
+      if(table_e == upb_inttable_mainpos(table, table_e->key)) {
         /* Existing element is in its main posisiton.  Find an empty slot to
-         * place our new element. */
+         * place our new element and append it to this key's chain. */
+        struct upb_inttable_entry *empty = find_empty_slot(table);
+        while (table_e->next) table_e = table_e->next;
+        table_e->next = empty;
+        table_e = empty;
       } else {
         /* Existing element is not in its main position.  Move it to an empty
          * slot and put our element in its main position. */
+        struct upb_inttable_entry *empty, *colliding_key_mainpos;
+        empty = find_empty_slot(table);
+        colliding_key_mainpos = upb_inttable_mainpos(table, table_e->key);
+        assert(colliding_key_mainpos->key != UPB_EMPTY_ENTRY);
+        assert(colliding_key_mainpos->next);
+        memcpy(empty, table_e, entry_size);  /* next is copied also. */
+        while(1) {
+          assert(colliding_key_mainpos->next);
+          if(colliding_key_mainpos->next == table_e) {
+            colliding_key_mainpos->next = empty;
+            break;
+          }
+        }
+        /* table_e remains set to our mainpos. */
       }
     }
+    memcpy(table_e, e, entry_size);
+    table_e->next = NULL;
   }
 }
 
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