[Chapter20&Hash] - Adding the hashmaps

clox/object.c

@@ -3,6 +3,7 @@
 
 #include "memory.h"
 #include "object.h"
+#include "table.h"
 #include "value.h"
 #include "vm.h"
 
@@ -18,21 +19,45 @@ static Obj* allocateObject(size_t size, ObjType type) {
   return object;
 }
 
-
-static ObjString* allocateString(char* chars, int length) {
+static ObjString* allocateString(char* chars, int length,
+                                 uint32_t hash)
+{
   ObjString* string = ALLOCATE_OBJ(ObjString, OBJ_STRING);
   string->length = length;
   string->chars = chars;
+  string->hash = hash;
+  tableSet(&vm.strings, string, NIL_VAL);
   return string;
 }
+static uint32_t hashString(const char* key, int length) {
+  uint32_t hash = 2166136261u;
+  for (int i = 0; i < length; i++) {
+    hash ^= (uint8_t)key[i];
+    hash *= 16777619;
+  }
+  return hash;
+}
 ObjString* takeString(char* chars, int length) {
-  return allocateString(chars, length);
+  uint32_t hash = hashString(chars, length);
+  ObjString* interned = tableFindString(&vm.strings, chars, length,
+                                        hash);
+  if (interned != NULL) {
+    FREE_ARRAY(char, chars, length + 1);
+    return interned;
+  }
+
+  return allocateString(chars, length, hash);
 }
 ObjString* copyString(const char* chars, int length) {
+  uint32_t hash = hashString(chars, length);
+  ObjString* interned = tableFindString(&vm.strings, chars, length,
+                                        hash);
+  if (interned != NULL) return interned;
+  
   char* heapChars = ALLOCATE(char, length + 1);
   memcpy(heapChars, chars, length);
   heapChars[length] = '\0';
-  return allocateString(heapChars, length);
+    return allocateString(heapChars, length, hash);
 }
 void printObject(Value value) {
   switch (OBJ_TYPE(value)) {

clox/object.h

@@ -21,7 +21,8 @@ struct Obj {
 struct ObjString {
   Obj obj;
   int length;
-  char* chars;
+  char* chars;  
+  uint32_t hash;
 };
 ObjString* takeString(char* chars, int length);
 ObjString* copyString(const char* chars, int length);

clox/table.c

@@ -0,0 +1,130 @@
+#include <stdlib.h>
+#include <string.h>
+
+#include "memory.h"
+#include "object.h"
+#include "table.h"
+#include "value.h"
+
+#define TABLE_MAX_LOAD 0.75
+
+void initTable(Table* table) {
+  table->count = 0;
+  table->capacity = 0;
+  table->entries = NULL;
+}
+
+void freeTable(Table* table) {
+  FREE_ARRAY(Entry, table->entries, table->capacity);
+  initTable(table);
+}
+static Entry* findEntry(Entry* entries, int capacity,
+                        ObjString* key) {
+  uint32_t index = key->hash % capacity;
+  Entry* tombstone = NULL;
+  for (;;) {
+    Entry* entry = &entries[index];
+    if (entry->key == NULL) {
+      if (IS_NIL(entry->value)) {
+        // Empty entry.
+        return tombstone != NULL ? tombstone : entry;
+      } else {
+        // We found a tombstone.
+        if (tombstone == NULL) tombstone = entry;
+      }
+    } else if (entry->key == key) {
+      // We found the key.
+      return entry;
+    }
+
+    index = (index + 1) % capacity;
+  }
+}
+
+static void adjustCapacity(Table* table, int capacity) {
+  Entry* entries = ALLOCATE(Entry, capacity);
+  for (int i = 0; i < capacity; i++) {
+    entries[i].key = NULL;
+    entries[i].value = NIL_VAL;
+  }
+  table->count = 0;
+  for (int i = 0; i < table->capacity; i++) {
+    Entry* entry = &table->entries[i];
+    if (entry->key == NULL) continue;
+
+    Entry* dest = findEntry(entries, capacity, entry->key);
+    dest->key = entry->key;
+    dest->value = entry->value;
+    table->count++;
+  }
+  FREE_ARRAY(Entry, table->entries, table->capacity);
+  table->entries = entries;
+  table->capacity = capacity;
+}
+bool tableGet(Table* table, ObjString* key, Value* value) {
+  if (table->count == 0) return false;
+
+  Entry* entry = findEntry(table->entries, table->capacity, key);
+  if (entry->key == NULL) return false;
+
+  *value = entry->value;
+  return true;
+}
+bool tableSet(Table* table, ObjString* key, Value value) {
+  if (table->count + 1 > table->capacity * TABLE_MAX_LOAD) {
+    int capacity = GROW_CAPACITY(table->capacity);
+    adjustCapacity(table, capacity);
+  }
+
+  Entry* entry = findEntry(table->entries, table->capacity, key);
+  bool isNewKey = entry->key == NULL;
+    if (isNewKey && IS_NIL(entry->value)) table->count++;
+
+  entry->key = key;
+  entry->value = value;
+  return isNewKey;
+}
+
+bool tableDelete(Table* table, ObjString* key) {
+  if (table->count == 0) return false;
+
+  // Find the entry.
+  Entry* entry = findEntry(table->entries, table->capacity, key);
+  if (entry->key == NULL) return false;
+
+  // Place a tombstone in the entry.
+  entry->key = NULL;
+  entry->value = BOOL_VAL(true);
+  return true;
+}
+
+
+void tableAddAll(Table* from, Table* to) {
+  for (int i = 0; i < from->capacity; i++) {
+    Entry* entry = &from->entries[i];
+    if (entry->key != NULL) {
+      tableSet(to, entry->key, entry->value);
+    }
+  }
+}
+
+ObjString* tableFindString(Table* table, const char* chars,
+                           int length, uint32_t hash) {
+  if (table->count == 0) return NULL;
+
+  uint32_t index = hash % table->capacity;
+  for (;;) {
+    Entry* entry = &table->entries[index];
+    if (entry->key == NULL) {
+      // Stop if we find an empty non-tombstone entry.
+      if (IS_NIL(entry->value)) return NULL;
+    } else if (entry->key->length == length &&
+        entry->key->hash == hash &&
+        memcmp(entry->key->chars, chars, length) == 0) {
+      // We found it.
+      return entry->key;
+    }
+
+    index = (index + 1) % table->capacity;
+  }
+}

clox/table.h

@@ -0,0 +1,26 @@
+#ifndef clox_table_h
+#define clox_table_h
+
+#include "common.h"
+#include "value.h"
+
+typedef struct {
+  ObjString* key;
+  Value value;
+} Entry;
+
+typedef struct {
+  int count;
+  int capacity;
+  Entry* entries;
+} Table;
+
+void initTable(Table* table);
+void freeTable(Table* table);
+bool tableGet(Table* table, ObjString* key, Value* value);
+bool tableSet(Table* table, ObjString* key, Value value);
+bool tableDelete(Table* table, ObjString* key);
+void tableAddAll(Table* from, Table* to);
+ObjString* tableFindString(Table* table, const char* chars,
+                           int length, uint32_t hash);
+#endif

clox/value.c

@@ -42,13 +42,7 @@ bool valuesEqual(Value a, Value b) {
     case VAL_BOOL:   return AS_BOOL(a) == AS_BOOL(b);
     case VAL_NIL:    return true;
     case VAL_NUMBER: return AS_NUMBER(a) == AS_NUMBER(b);
-    case VAL_OBJ: {
-      ObjString* aString = AS_STRING(a);
-      ObjString* bString = AS_STRING(b);
-      return aString->length == bString->length &&
-          memcmp(aString->chars, bString->chars,
-                 aString->length) == 0;
-    }
+    case VAL_OBJ:    return AS_OBJ(a) == AS_OBJ(b);
     default:         return false; // Unreachable.
   }
 }

clox/vm.c

@@ -28,9 +28,11 @@ static void runtimeError(const char* format, ...) {
 void initVM() {
   resetStack();
   vm.objects = NULL;
+  initTable(&vm.strings);
 }
 
 void freeVM() {
+  freeTable(&vm.strings);
   freeObjects();
 }
 void push(Value value) {

clox/vm.h

@@ -2,6 +2,7 @@
 #define clox_vm_h
 
 #include "chunk.h"
+#include "table.h"
 #include "value.h"
 
 #define STACK_MAX 256
@@ -11,6 +12,7 @@ typedef struct {
   uint8_t* ip;
   Value stack[STACK_MAX];
   Value* stackTop;
+  Table strings;
   Obj* objects;
 } VM;
 typedef enum {