From 0dfaa80f87f7135dd9c393b9070969818999fb73 Mon Sep 17 00:00:00 2001
From: ZhuangYumin <zhuangyumin@sjtu.edu.cn>
Date: Thu, 7 Dec 2023 14:57:43 +0000
Subject: [PATCH] docs: further optimize key2index

---
 backend/include/key2index.hpp | 97 +++++++++++------------------------
 1 file changed, 30 insertions(+), 67 deletions(-)

diff --git a/backend/include/key2index.hpp b/backend/include/key2index.hpp
index 322a66f..55de193 100644
--- a/backend/include/key2index.hpp
+++ b/backend/include/key2index.hpp
@@ -24,28 +24,15 @@ class String2Index {
 
   struct Node {
     size_t main_hash, sub_hash;
-    int val;
+    int val, nxt_idx = 0;
     Node() = default;
     Node(std::string str, int _val)
         : main_hash(Hash(str)),
           sub_hash(Hash(sub_salt1 + str + sub_salt2)),
           val(_val) {}
   };
-  static const int kNodesPerBlock =
-      (kPageSize - 3 * sizeof(int)) / sizeof(Node);
 
-  struct Block {
-    int tot, nxt_idx;
-    Node data[kNodesPerBlock];
-    // char padding[kPageSize - 3 * sizeof(int) - sizeof(Node) *
-    // (kNodesPerBlock)];
-    Block() : tot(0), nxt_idx(0) {}
-    Block(int _tot, int _nxt_idx) : tot(_tot), nxt_idx(_nxt_idx) {}
-  };
-  static_assert(kNodesPerBlock >= 1, "kNodesPerBlock error");
-  static_assert(sizeof(Block) <= kPageSize - 4, "Block Size error");
-
-  DriveArray<Block, kBucketSize, 100> mem;
+  DriveArray<Node, kBucketSize, 100> mem;
   int *hash_table = nullptr;
   std::string file_name;
 
@@ -85,78 +72,54 @@ class String2Index {
   void Insert(const std::string &str, int val) noexcept {
     size_t hash_val = Hash(str);
     int idx = hash_table[hash_val % kBucketSize];
-    Block *blk_ptr = new Block;
+    Node nd(str, val);
     if (idx == 0) {
-      Block __Init_Block;
-      idx = mem.write(__Init_Block);
+      idx = mem.write(nd);
       hash_table[hash_val % kBucketSize] = idx;
-      assert(idx >= 1);
-    }
-    mem.read(*blk_ptr, idx);
-    if (blk_ptr->tot == kNodesPerBlock) {
-      Block __New_Head_Block(0, idx);
-      idx = mem.write(__New_Head_Block);
+    } else {
+      nd.nxt_idx = idx;
+      idx = mem.write(nd);
       hash_table[hash_val % kBucketSize] = idx;
-      mem.read(*blk_ptr, idx);
     }
-    blk_ptr->data[blk_ptr->tot++] = Node(str, val);
-    mem.update(*blk_ptr, idx);
-    delete blk_ptr;
   }
   void Delete(const std::string &str, int val) noexcept {
-    size_t hash_val = Hash(str);
-    int idx = hash_table[hash_val % kBucketSize];
-    Block *blk_ptr = new Block;
     size_t str_main_hash = Hash(str),
            str_sub_hash = Hash(sub_salt1 + str + sub_salt2);
+    int idx = hash_table[str_main_hash % kBucketSize];
+    Node nd, last_nd;
+    int last_idx = -1;
     while (idx != 0) {
-      mem.read(*blk_ptr, idx);
-      for (int i = 0; i < blk_ptr->tot; ++i) {
-        if (blk_ptr->data[i].main_hash == str_main_hash &&
-            blk_ptr->data[i].sub_hash == str_sub_hash &&
-            blk_ptr->data[i].val == val) {
-          int headidx = hash_table[hash_val % kBucketSize];
-          if (headidx == idx) {
-            blk_ptr->data[i] = blk_ptr->data[--blk_ptr->tot];
-            mem.update(*blk_ptr, idx);
-          } else {
-            Block *head_blk_ptr = new Block;
-            mem.read(*head_blk_ptr, headidx);
-            blk_ptr->data[i] = head_blk_ptr->data[--head_blk_ptr->tot];
-            if (head_blk_ptr->tot == 0) {
-              hash_table[hash_val % kBucketSize] = head_blk_ptr->nxt_idx;
-              mem.Delete(headidx);
-            } else
-              mem.update(*head_blk_ptr, headidx);
-            mem.update(*blk_ptr, idx);
-            delete head_blk_ptr;
-          }
-          delete blk_ptr;
-          return;
+      mem.read(nd, idx);
+      if (nd.main_hash == str_main_hash && nd.sub_hash == str_sub_hash &&
+          nd.val == val) {
+        if (last_idx == -1) {
+          hash_table[str_main_hash % kBucketSize] = nd.nxt_idx;
+          mem.Delete(idx);
+        } else {
+          last_nd.nxt_idx = nd.nxt_idx;
+          mem.update(last_nd, last_idx);
+          mem.Delete(idx);
         }
+        return;
       }
-      idx = blk_ptr->nxt_idx;
+      last_idx = idx;
+      last_nd = nd;
+      idx = nd.nxt_idx;
     }
-    delete blk_ptr;
   }
   std::vector<int> Find(const std::string &str) noexcept {
     std::vector<int> ret;
-    size_t hash_val = Hash(str);
-    int idx = hash_table[hash_val % kBucketSize];
-    Block *blk_ptr = new Block;
     size_t str_main_hash = Hash(str),
            str_sub_hash = Hash(sub_salt1 + str + sub_salt2);
+    int idx = hash_table[str_main_hash % kBucketSize];
+    Node nd;
     while (idx != 0) {
-      mem.read(*blk_ptr, idx);
-      for (int i = 0; i < blk_ptr->tot; ++i) {
-        if (blk_ptr->data[i].main_hash == str_main_hash &&
-            blk_ptr->data[i].sub_hash == str_sub_hash) {
-          ret.push_back(blk_ptr->data[i].val);
-        }
+      mem.read(nd, idx);
+      if (nd.main_hash == str_main_hash && nd.sub_hash == str_sub_hash) {
+        ret.push_back(nd.val);
       }
-      idx = blk_ptr->nxt_idx;
+      idx = nd.nxt_idx;
     }
-    delete blk_ptr;
     return std::move(ret);
   }
 };