pebblisp/src/hash.c

#include "hash.h"
#include "env.h"
#include "pebblisp.h"
#include "object.h"

#include <string.h>
#include <stdio.h>

size_t addStripped(struct ObjectTable* table, char* name, struct StrippedObject object);

Object deStrip(struct StrippedObject object)
{
    // Garbage .forward data may be safe here, but since usage of that data is
    // currently in flux, it should take the more cautious route for now.
    return (Object) {
        .type = object.type,
        .string = object.data,
        .forward = NULL,
    };
}

struct ObjectTable buildTable(size_t capacity)
{
    struct ObjectTable table = {
        .count = 0,
        .capacity = capacity,
        .elements = capacity ? malloc(sizeof(struct EnvElement) * capacity) : NULL,
    };
    for (int i = 0; i < table.capacity; i++) {
        table.elements[i].symbol = NULL;
    }
    return table;
}

void deleteTable(struct ObjectTable* table)
{
    for (int i = 0; i < table->capacity; i++) {
        if (table->elements[i].symbol) {
            free(table->elements[i].symbol);
            Object deStripped = deStrip(table->elements[i].object);
            cleanObject(&deStripped);
        }
    }
    free(table->elements);
}

#ifndef HASHLESS_ENV

size_t hash(const char* str, unused const struct ObjectTable* table)
{
    size_t hash = 5381;
    char c;

    while ((c = *str++)) {
        hash = ((hash << 5) + hash) + c; /* hash * 33 + c */
    }

    return hash;
}

void extendTable(struct ObjectTable* table)
{
    if (table->capacity >= (table->count + 1) * 2) {
        return;
    }

    struct ObjectTable newTable = buildTable(table->capacity ? table->capacity * 2 : 4);
    for (int i = 0; i < table->capacity; i++) {
        if (table->elements[i].symbol) {
            addStripped(&newTable, table->elements[i].symbol, table->elements[i].object);
        }
    }
    free(table->elements);
    *table = newTable;
}

struct StrippedObject* getFromTable(struct ObjectTable* table, const char* name)
{
    if (table->capacity == 0) {
        return NULL;
    }
    size_t h = hash(name, table) % table->capacity;
    while (table->elements[h].symbol) {
        if (strcmp(name, table->elements[h].symbol) == 0) {
            return &table->elements[h].object;
        }
        h = (h + 1) % table->capacity;
    }
    return NULL;
}

#else

void extendTable(struct ObjectTable* table)
{
    if (table->count == (table->capacity - 1)) {
        struct EnvElement* oldElements = table->elements;
        size_t oldCapacity = table->capacity;
        table->capacity *= 2;
        table->elements = malloc(sizeof(struct EnvElement) * table->capacity);
        for (int i = 0; i < oldCapacity; i++) {
            table->elements[i] = oldElements[i];
        }
        for (size_t i = oldCapacity; i < table->capacity; i++) {
            table->elements[i].symbol = NULL;
        }
        free(oldElements);
    }
}

struct StrippedObject* getFromTable(struct ObjectTable* table, const char* name)
{
    for (size_t i = 0; i < table->count; i++) {
        if (strcmp(name, table->elements[i].symbol) == 0) {
            return &table->elements[i].object;
        }
    }
    return NULL;
}

static size_t hash(unused const char* str, struct ObjectTable* table)
{
    return table->count;
}

#endif

/**
 * \return The hash value of the given name
 */
size_t addStripped(struct ObjectTable* table, char* name, struct StrippedObject object)
{
    extendTable(table);
    size_t initial = hash(name, table);
    size_t h = initial % table->capacity;
    while (table->elements[h].symbol && strcmp(table->elements[h].symbol, name) != 0) {
        h = (h + 1) % table->capacity;
    }

    if (table->elements[h].symbol) {
        Object previous = deStrip(table->elements[h].object);
        cleanObject(&previous);
        free(table->elements[h].symbol);
    }

    table->elements[h].symbol = name;
    table->elements[h].object = object;
    table->count += 1;
    return initial;
}

size_t addToTable(struct ObjectTable* table, char* name, Object object)
{
    return addStripped(table, name, (struct StrippedObject) {
        .data = object.data,
        .type = object.type,
    });
}

#ifdef STANDALONE

int isHash(const Object test)
{
    return test.type == TYPE_HASH_TABLE;
}

Object buildHashTable(Object* params, int length, struct Environment* env)
{
    long capacity = 16;
    if (length > 0 && params[0].type == TYPE_NUMBER) {
        capacity = params[0].number;
    }

    Object table = newObject(TYPE_HASH_TABLE);
    table.table = malloc(sizeof(struct ObjectTableObject));
    table.table->table = buildTable(capacity);
    table.table->refs = 1;

    return table;
}

Object addToHashTable(Object* params, int length, struct Environment* env)
{
    checkTypes(addToHashTable)

    Object name = params[1];
    Object add = params[2];

    struct ObjectTable* table = &params[0].table->table;
    addToTable(table, strdup(name.string), cloneObject(add));
    return numberObject(0);
}

Object getFromHashTable(Object* params, int length, struct Environment* env)
{
    checkTypes(getFromHashTable)

    struct ObjectTable* table = &params[0].table->table;
    struct StrippedObject* fetched = getFromTable(table, params[1].string);

    if (fetched) {
        return cloneObject(deStrip(*fetched));
    }

    throw(DID_NOT_FIND_SYMBOL, "Hash table does not contain %s", params[1].string);
}

#endif