power_play/src/util.h

#ifndef UTIL_H
#define UTIL_H

#include "sys.h"
#include "string.h"
#include "memory.h"
#include "arena.h"
#include "atomic.h"
#include "math.h"
#include "scratch.h"

/* Utility functions and stuff that don't have a home :( */

/* ========================== *
 * Hash utils
 * ========================== */

/* FNV-1a parameters for different hash sizes:
 * https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function#FNV_hash_parameters
 */

#define HASH_FNV64_BASIS 0xCBF29CE484222325
INLINE u64 hash_fnv64(u64 seed, struct string s)
{
    u64 hash = seed;
    for (u64 i = 0; i < s.len; ++i) {
        hash ^= (u8)s.text[i];
        hash *= 0x100000001B3;
    }
    return hash;
}

/* ========================== *
 * Merge sort
 * ========================== */

/* Compare functions should
 * return an int < 0 if a <  b
 * return an int = 0 if a == b
 * return an int > 0 if a > b
 */
#define SORT_COMPARE_FUNC_DEF(name, arg_a, arg_b, arg_udata) i32 name(void *arg_a, void *arg_b, void *arg_udata)
typedef SORT_COMPARE_FUNC_DEF(sort_compare_func, a, b, udata);

INLINE void merge_sort_internal(u8 *left, u8 *right, u8 *items, u64 left_count, u64 right_count, u64 item_size, sort_compare_func *callback, void *udata)
{
    /* Sort */
    u64 i = 0;
    u64 l = 0;
    u64 r = 0;
    while (l < left_count && r < right_count) {
        u8 *dst = items + (i * item_size);
        u8 *left_item = left + (l * item_size);
        u8 *right_item = right + (r * item_size);
        ++i;
        if (callback(left_item, right_item, udata) > 0) {
            MEMCPY(dst, left_item, item_size);
            ++l;
        } else {
            MEMCPY(dst, right_item, item_size);
            ++r;
        }
    }
    /* Copy remaining */
    if (l != left_count) {
        u64 remaining_count = left_count - l;
        u64 remaining_bytes = remaining_count * item_size;
        u8 *dst = items + (i * item_size);
        u8 *src = left + (l * item_size);
        MEMCPY(dst, src, remaining_bytes);
    } else if (r != right_count) {
        u64 remaining_count = right_count - r;
        u64 remaining_bytes = remaining_count * item_size;
        u8 *dst = items + (i * item_size);
        u8 *src = right + (r * item_size);
        MEMCPY(dst, src, remaining_bytes);
    }
}

INLINE void merge_sort(void *items, u64 item_count, u64 item_size, sort_compare_func *callback, void *udata)
{
    if (item_count > 1) {
        struct temp_arena scratch = scratch_begin_no_conflict();
        u64 left_count = item_count / 2;
        u64 right_count = item_count - left_count;

        u64 left_size = left_count * item_size;
        u64 right_size = right_count * item_size;

        u8 *left = arena_push_array_no_zero(scratch.arena, u8, left_size);
        u8 *right = arena_push_array_no_zero(scratch.arena, u8, right_size);
        MEMCPY(left, items, left_size);
        MEMCPY(right, (u8 *)items + left_size, right_size);

        merge_sort(left, left_count, item_size, callback, udata);
        merge_sort(right, right_count, item_size, callback, udata);
        merge_sort_internal(left, right, (u8 *)items, left_count, right_count, item_size, callback, udata);
        scratch_end(scratch);
    }
}

/* ========================== *
 * Fixed Dict
 *
 * Simple fixed-bin-count string -> pointer chaining hash table for generic use
 * ========================== */

struct fixed_dict_entry {
    struct string key;
    void *value;
    u64 hash;
    struct fixed_dict_entry *next;
};

struct fixed_dict_bin {
    struct fixed_dict_entry *entry_head;
};

struct fixed_dict {
    u64 bins_count;
    struct fixed_dict_bin *bins;
};

INLINE struct fixed_dict fixed_dict_init(struct arena *arena, u64 bins_count)
{
    __prof;
    struct fixed_dict dict = ZI;
    bins_count = max_u64(bins_count, 1);  /* Ensure at least 1 bin */
    dict.bins_count = bins_count;
    dict.bins = arena_push_array(arena, struct fixed_dict_bin, bins_count);
    return dict;
}

/* arena and key must share lifetime with dict (this function does not copy the key) */
INLINE void fixed_dict_set(struct arena *arena, struct fixed_dict *dict, struct string key, void *value)
{
    __prof;

    u64 hash = hash_fnv64(HASH_FNV64_BASIS, key);
    u64 index = hash % dict->bins_count;
    struct fixed_dict_bin *bin = &dict->bins[index];

    struct fixed_dict_entry *entry = bin->entry_head;
    while (entry) {
        if (hash == entry->hash) {
            /* Existing match found, replace its contents */
            entry->key = key;
            entry->value = value;
            return;
        }
        entry = entry->next;
    }

    /* No match found, create new entry */
    entry = arena_push_no_zero(arena, struct fixed_dict_entry);
    entry->key = key;
    entry->value = value;
    entry->hash = hash;
    entry->next = bin->entry_head;

    bin->entry_head = entry;
}

INLINE void *fixed_dict_get(const struct fixed_dict *dict, struct string key)
{
    __prof;

    u64 hash = hash_fnv64(HASH_FNV64_BASIS, key);
    u64 index = hash % dict->bins_count;
    struct fixed_dict_bin *bin = &dict->bins[index];

    for (struct fixed_dict_entry *entry = bin->entry_head; entry; entry = entry->next) {
        if (hash == entry->hash) {
            /* Match found */
            return entry->value;
        }
    }

    return NULL;
}

/* ========================== *
 * Sync flag
 * ========================== */

struct sync_flag {
    struct sys_mutex mutex;
    struct sys_condition_variable cv;
    b32 flag;
};

INLINE struct sync_flag sync_flag_alloc(void)
{
    struct sync_flag sf = ZI;
    sf.mutex = sys_mutex_alloc();
    sf.cv = sys_condition_variable_alloc();
    return sf;
}

INLINE void sync_flag_release(struct sync_flag *sf)
{
    sys_mutex_release(&sf->mutex);
    sys_condition_variable_release(&sf->cv);
}

INLINE void sync_flag_set(struct sync_flag *sf)
{
    __prof;
    struct sys_lock lock = sys_mutex_lock_e(&sf->mutex);
    sf->flag = 1;
    sys_condition_variable_broadcast(&sf->cv);
    sys_mutex_unlock(&lock);
}

INLINE void sync_flag_wait(struct sync_flag *sf)
{
    __prof;
    struct sys_lock lock = sys_mutex_lock_s(&sf->mutex);
    while (sf->flag != 1) {
        sys_condition_variable_wait(&sf->cv, &lock);
    }
    sys_mutex_unlock(&lock);
}

/* ========================== *
 * Sleep frame
 * ========================== */

INLINE void sleep_frame(i64 last_frame_time_ns, i64 target_dt_ns)
{
    __prof;
    if (last_frame_time_ns != 0 && target_dt_ns > 0) {
        i64 now_ns = sys_time_ns();
        i64 last_frame_dt_ns = now_ns - last_frame_time_ns;
        i64 sleep_time_ns = target_dt_ns - last_frame_dt_ns;
        if (sleep_time_ns > 0) {
            sys_sleep_precise(SECONDS_FROM_NS(sleep_time_ns));
        }
    }
}

#endif