table.c

#include <stdint.h>
#include <stdlib.h>
#include <string.h>

#include "table.h"
#include "memory.h"
#include "value.h"

#define TABLE_MAX_LOAD 0.75 /* This will manage the table's load factor */

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);
}

/*
    This function’s job is to take a key and figure out which bucket in the array it should go in. 
    It returns a pointer to that bucket—the address of the Entry in the array.
*/
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 = dest->value;
    }
    
    FREE_ARRAY(Entry, table->entries, table->capacity);
    table->entries = entries;
    table->capacity = capacity;
}

bool tableSet(Table* table, ObjString* key, Value value) {
    /* We grow the array when it becomes at least 75% full */
    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;
    
    /* If the key already exists the value will overwrite the old one */
    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;
}

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;
}

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 and 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;
    }
}