Cosmo/src/ctable.c

#include "ctable.h"
#include "cmem.h"
#include "cvalue.h"
#include "cobj.h"

#include <string.h>

#define MAX_TABLE_FILL 0.75
// at 30% capacity with capacity > ARRAY_START, shrink the array
#define MIN_TABLE_CAPACITY ARRAY_START

// bit-twiddling hacks, gets the next power of 2
unsigned int nextPow2(unsigned int x) {
    if (x <= ARRAY_START - 1) return ARRAY_START; // sanity check
    x--;

    int power = 2;
    while (x >>= 1) power <<= 1;

    if (power < ARRAY_START)
        return ARRAY_START;

    return power;
}

void cosmoT_initTable(CState *state, CTable *tbl, int startCap) {
    tbl->capacity = startCap != 0 ? startCap : ARRAY_START; // sanity check :P
    tbl->count = 0;
    tbl->tombstones = 0;
    tbl->table = NULL; // to let out GC know we're initalizing
    tbl->table = cosmoM_xmalloc(state, sizeof(CTableEntry) * tbl->capacity);

    // init everything to NIL
    for (int i = 0; i < tbl->capacity; i++) {
        tbl->table[i].key = cosmoV_newNil();
        tbl->table[i].val = cosmoV_newNil();
    }
}

void cosmoT_addTable(CState *state, CTable *from, CTable *to) {
    for (int i = 0; i < from->capacity; i++) {
        CTableEntry *entry = &from->table[i];

        if (!(IS_NIL(entry->key))) {
            CValue *newVal = cosmoT_insert(state, to, entry->key);
            *newVal = entry->val;
        }
    }
}

void cosmoT_clearTable(CState *state, CTable *tbl) {
    cosmoM_freearray(state, CTableEntry, tbl->table, tbl->capacity);
}

uint32_t getObjectHash(CObj *obj) {
    switch(obj->type) {
        case COBJ_STRING:
            return ((CObjString*)obj)->hash;
        default:
            return 0;
    }
}

uint32_t getValueHash(CValue *val) {
    switch (val->type) {
        case COSMO_TOBJ:
            return getObjectHash(val->val.obj);
        case COSMO_TNUMBER: {
            uint32_t buf[sizeof(cosmo_Number)/sizeof(uint32_t)];
            if (val->val.num == 0)
                return 0;
            memcpy(buf, &val->val.num, sizeof(buf));
            for (int i = 0; i < sizeof(cosmo_Number)/sizeof(uint32_t); i++) buf[0] += buf[i];
            return buf[0];
        }
            
        // TODO: add support for other types
        default:
            return 0;
    }
}

// mask should always be (capacity - 1)
static CTableEntry *findEntry(CTableEntry *entries, int mask, CValue key) {
    uint32_t hash = getValueHash(&key);
    uint32_t indx = hash & mask; // since we know the capacity will *always* be a power of 2, we can use bitwise & to perform a MUCH faster mod operation
    CTableEntry *tomb = NULL;

    // keep looking for an open slot in the entries array
    while (true) {
        CTableEntry *entry = &entries[indx];

        if (IS_NIL(entry->key)) {
            // check if it's an empty bucket or a tombstone
            if (IS_NIL(entry->val)) {
                // it's empty! if we found a tombstone, return that so it'll be reused
                return tomb != NULL ? tomb : entry;
            } else {
                // its a tombstone!
                tomb = entry;
            }
        } else if (cosmoV_equal(entry->key, key)) {
            return entry;
        }

        indx = (indx + 1) & mask; // fast mod here too
    }
}

static void resizeTbl(CState *state, CTable *tbl, size_t newCapacity) {
    CTableEntry *entries = cosmoM_xmalloc(state, sizeof(CTableEntry) * newCapacity);

    /* Before someone asks, no we shouldn't move the tombstone check to before the entries allocation.
    The garbage collector is threshhold based, based on the currently allocated bytes. There's an 
    edgecase where if GC_STRESS is not enabled the GC will really only be called on growth of the 
    string interning table (this.) However the new size of the table is accounted for in the next threshhold
    cycle, causing allocations to become less and less frequent until your computer develops dementia.
    */

    // if count > 8 and active entries < tombstones 
    if (tbl->count > MIN_TABLE_CAPACITY && tbl->count - tbl->tombstones < tbl->tombstones) {
        cosmoM_freearray(state, CTableEntry, entries, newCapacity);
        int tombs = tbl->tombstones;
        tbl->tombstones = 0;
        resizeTbl(state, tbl, nextPow2((tbl->count - tombs) * GROW_FACTOR));
        cosmoM_updateThreshhold(state); // force a threshhold update since this *could* be such a huge memory difference
        return;
    }

    int newCount = 0;

    // set all nodes as NIL : NIL
    for (int i = 0; i < newCapacity; i++) {
        entries[i].key = cosmoV_newNil();
        entries[i].val = cosmoV_newNil();
    }

    // move over old values to the new buffer
    for (int i = 0; i < tbl->capacity; i++) {
        CTableEntry *oldEntry = &tbl->table[i];
        if (IS_NIL(oldEntry->key))
            continue; // skip empty keys

        // get new entry location & update the node
        CTableEntry *newEntry = findEntry(entries, newCapacity - 1, oldEntry->key);
        newEntry->key = oldEntry->key;
        newEntry->val = oldEntry->val;
        newCount++; // inc count
    }

    // free the old table
    cosmoM_freearray(state, CTableEntry, tbl->table, tbl->capacity);

    tbl->table = entries;
    tbl->capacity = newCapacity;
    tbl->count = newCount;
    tbl->tombstones = 0;
}

// returns a pointer to the allocated value
COSMO_API CValue* cosmoT_insert(CState *state, CTable *tbl, CValue key) {
    // make sure we have enough space allocated
    if (tbl->count + 1 > (int)(tbl->capacity * MAX_TABLE_FILL)) {
        // grow table
        int newCap = tbl->capacity * GROW_FACTOR;
        resizeTbl(state, tbl, newCap);
    }

    // insert into the table
    CTableEntry *entry = findEntry(tbl->table, tbl->capacity - 1, key); // -1 for our capacity mask

    if (IS_NIL(entry->key) && IS_NIL(entry->val)) // is it empty?
        tbl->count++;

    entry->key = key;
    return &entry->val;
}

bool cosmoT_get(CTable *tbl, CValue key, CValue *val) {
    if (tbl->count == 0) {
        *val = cosmoV_newNil();
        return false; // sanity check
    }
    
    CTableEntry *entry = findEntry(tbl->table, tbl->capacity - 1, key);
    *val = entry->val;
    
    return !(IS_NIL(entry->key));
}

bool cosmoT_remove(CState* state, CTable *tbl, CValue key) {
    if (tbl->count == 0) return 0; // sanity check

    CTableEntry *entry = findEntry(tbl->table, tbl->capacity - 1, key);
    if (IS_NIL(entry->key)) // sanity check
        return false;

    // crafts tombstone
    entry->key = cosmoV_newNil(); // this has to be nil
    entry->val = cosmoV_newBoolean(false); // doesn't reall matter what this is, as long as it isn't nil
    tbl->tombstones++;

    return true;
}

CObjString *cosmoT_lookupString(CTable *tbl, const char *str, size_t length, uint32_t hash) {
    if (tbl->count == 0) return 0; // sanity check
    uint32_t indx = hash & (tbl->capacity - 1); // since we know the capacity will *always* be a power of 2, we can use bitwise & to perform a MUCH faster mod operation

    // keep looking for an open slot in the entries array
    while (true) {
        CTableEntry *entry = &tbl->table[indx];

        // check if it's an empty slot (meaning we dont have it in the table)
        if (IS_NIL(entry->key) && IS_NIL(entry->val)) {
            return NULL;
        } else if (IS_STRING(entry->key) && cosmoV_readString(entry->key)->length == length && memcmp(cosmoV_readString(entry->key)->str, str, length) == 0) {
            // it's a match!
            return (CObjString*)entry->key.val.obj;
        }

        indx = (indx + 1) & (tbl->capacity - 1); // fast mod here too
    }
}

// for debugging purposes
void cosmoT_printTable(CTable *tbl, const char *name) {
    printf("==== [[%s]] ====\n", name);
    for (int i = 0; i < tbl->capacity; i++) {
        CTableEntry *entry = &tbl->table[i];
        if (!(IS_NIL(entry->key))) {
            printValue(entry->key);
            printf(" - ");
            printValue(entry->val);
            printf("\n");
        }
    }
}