java-topology/defects/xonotic-0004/test/test_s_findname.c

/**
 * Unit test for xonotic-0004: S_FindName O(N) linked list scan.
 *
 * Defect: snd_main.c S_FindName() traverses a linked list of known sfx entries
 * to find a sound by name. The code itself has a "TODO: hash table search?"
 * comment. Called every time a sound is played, precached, or referenced.
 * With many sounds loaded, each lookup is O(N).
 *
 * Fix: hash table on sfx name for O(1) average lookup.
 */

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

#define MAX_SFX 2000
#define NUM_LOOKUPS 100000
#define SFX_HASHSIZE 256

typedef struct sfx_s {
    char name[64];
    struct sfx_s *next;
    struct sfx_s *hashnext;
} sfx_t;

static sfx_t sfx_pool[MAX_SFX];
static sfx_t *known_sfx = NULL;
static sfx_t *sfx_hashtable[SFX_HASHSIZE];

static unsigned sfx_hash(const char *name)
{
    unsigned hash = 0;
    const unsigned char *p;
    for (p = (const unsigned char *)name; *p; p++)
        hash = hash * 31 + *p;
    return hash % SFX_HASHSIZE;
}

/* Unpatched: O(N) linked list scan */
static sfx_t *find_sfx_linear(const char *name)
{
    sfx_t *sfx;
    for (sfx = known_sfx; sfx != NULL; sfx = sfx->next)
        if (!strcmp(sfx->name, name))
            return sfx;
    return NULL;
}

/* Patched: O(1) hash lookup */
static sfx_t *find_sfx_hash(const char *name)
{
    unsigned h = sfx_hash(name);
    sfx_t *sfx;
    for (sfx = sfx_hashtable[h]; sfx != NULL; sfx = sfx->hashnext)
        if (!strcmp(sfx->name, name))
            return sfx;
    return NULL;
}

int main(void)
{
    int i, pass = 1;
    clock_t start, end;
    double linear_time, hash_time, ratio;

    /* Build linked list and hash table */
    memset(sfx_hashtable, 0, sizeof(sfx_hashtable));
    known_sfx = NULL;

    for (i = 0; i < MAX_SFX; i++)
    {
        sfx_t *s = &sfx_pool[i];
        snprintf(s->name, sizeof(s->name), "sounds/fx/effect_%04d.ogg", i);
        s->next = known_sfx;
        known_sfx = s;

        unsigned h = sfx_hash(s->name);
        s->hashnext = sfx_hashtable[h];
        sfx_hashtable[h] = s;
    }

    /* Correctness */
    for (i = 0; i < MAX_SFX; i++)
    {
        sfx_t *lin = find_sfx_linear(sfx_pool[i].name);
        sfx_t *hsh = find_sfx_hash(sfx_pool[i].name);
        if (lin != hsh)
        {
            printf("FAIL: mismatch at sfx %d: linear=%p hash=%p\n", i, (void*)lin, (void*)hsh);
            pass = 0;
        }
    }

    /* Not-found */
    if (find_sfx_hash("nonexistent.wav") != NULL)
    {
        printf("FAIL: hash found nonexistent sfx\n");
        pass = 0;
    }
    if (find_sfx_linear("nonexistent.wav") != NULL)
    {
        printf("FAIL: linear found nonexistent sfx\n");
        pass = 0;
    }

    /* Benchmark */
    start = clock();
    for (i = 0; i < NUM_LOOKUPS; i++)
    {
        int idx = i % MAX_SFX;
        volatile sfx_t *r = find_sfx_linear(sfx_pool[idx].name);
        (void)r;
    }
    end = clock();
    linear_time = (double)(end - start) / CLOCKS_PER_SEC;

    start = clock();
    for (i = 0; i < NUM_LOOKUPS; i++)
    {
        int idx = i % MAX_SFX;
        volatile sfx_t *r = find_sfx_hash(sfx_pool[idx].name);
        (void)r;
    }
    end = clock();
    hash_time = (double)(end - start) / CLOCKS_PER_SEC;

    ratio = linear_time / (hash_time > 0 ? hash_time : 0.0001);

    printf("xonotic-0004: S_FindName linked list scan defect\n");
    printf("  SFX entries: %d, Lookups: %d\n", MAX_SFX, NUM_LOOKUPS);
    printf("  Linear: %.4fs, Hash: %.4fs, Ratio: %.1fx\n", linear_time, hash_time, ratio);

    if (ratio < 2.0)
    {
        printf("FAIL: expected hash lookup to be at least 2x faster (got %.1fx)\n", ratio);
        pass = 0;
    }

    printf("%s\n", pass ? "PASS" : "FAIL");
    return pass ? 0 : 1;
}