hashtable implementation in C uses open addressing, linear probing also includes a FNV1/DJB2 hashing comparison

hash.c

#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <time.h>
#include <assert.h>
#include <string.h>
#include <limits.h>
#include <inttypes.h>

uint32_t fnv1(const char *str)
{
	#define FNV_PRIME_32 16777619
	#define FNV_OFFSET_32 2166136261U
	
	uint32_t hash = FNV_OFFSET_32;
	int c;
	while((c = *str++)){
		hash ^= c;
		hash *= FNV_PRIME_32;
	}
	return hash;
	
	#undef FNV_OFFSET_32
	#undef FNV_PRIME_32
}

uint32_t djb2(const char *str)
{
	uint32_t hash = 5381;
	int c;
	
	while((c = *str++)) hash = ((hash << 5) + hash) + c;
	
	return hash;
}

typedef long long int modpow_t;
//Returns (b^e)%m
modpow_t modular_pow(modpow_t base, modpow_t exponent, modpow_t modulus)
{
	modpow_t result = 1;
	
	if(modulus == 1) return 0;
	
	//assert(UINT_MAX / (modulus - 1) > (modulus - 1));
	
	base %= modulus;
	while(exponent > 0){
		if(exponent & 1){
			result = (result * base) % modulus;
		}
		exponent >>= 1;
		base = (base * base) % modulus;
	}
	return result;
}

//Primality test
//Accurate at least up to 2 billion
int miller_rabin_test(int n)
{
	const int bases[] = {2, 7, 61};
	int r = 0, d = n - 1, i, j;
	
	assert(n < 2000000000);
	
	if(n == 2 || n == 3) return 1;
	if((n & 1) == 0 || n < 2) return 0;
	
	while(!(d & 1)){
		d >>= 1;
		r++;
	}
	for(j = 0; j < sizeof(bases) / sizeof(bases[0]); j++){
		int a = bases[j];
		int x = modular_pow(a, d, n);
		if(x == 1 || x == n - 1) continue;
		for(i = 1; i < r; i++){
			x = modular_pow(x, 2, n);
			if(x == n - 1) break;
		}
		if(i == r) return 0;
	}
	return 1;
}

//Returns a prime greater than
int get_prime_gt(int a)
{
	while(!miller_rabin_test(a)){
		a++;
	}
	return a;
}

typedef struct hashtable
{
	struct bucket
	{
		//Storing the hash allows for fast reinsertion
		uint32_t hash;
		//Currently stored as pointers to individual strings
		//If pointing to the very table buffer, means a previously deleted bucket
		char *key;
		void *val;
	} *table;
	//Hash func ptr
	uint32_t (*hash)(const char *);
	//Num of used buckets, total capacity
	int len, siz;
} hashtable;

//Create a hash table
hashtable *ht_create(int cap)
{
	hashtable *h = malloc(sizeof(*h));
	
	h->len = 0;
	h->siz = get_prime_gt(cap);
	h->table = malloc(sizeof(*h->table) * h->siz);
	memset(h->table, 0, sizeof(*h->table) * h->siz);
	
	return h;
}

//Destroys a hash table
void ht_destroy(hashtable *h)
{
	int i;
	
	for(i = 0; i < h->siz; i++){
		if(h->table[i].key && h->table[i].key != (char *) h->table){
			free(h->table[i].key);
		}
	}
	
	free(h->table);
	free(h);
}

//Searches for key, returns value or 0 if not found
void *ht_search(const hashtable *h, const char *k)
{
	int i;
	const int i0 = h->hash(k) % h->siz;
	
	i = i0;
	do {
		if(!h->table[i].key) break;
		if(h->table[i].key != (char *) h->table){
			if(!strcmp(h->table[i].key, k)) return h->table[i].val;
		}
		i = (i + 1) % h->siz;
	} while(i != i0);
	
	return 0;
}

//Grows the hashtable to new capacity
void ht_resize(hashtable *h, int new_cap)
{
	int j;
	hashtable *newh = ht_create(new_cap);
	
	for(j = 0; j < h->siz; j++){
		int i;
		const int i0 = h->table[j].hash % newh->siz;
		
		if(!h->table[j].key) continue;
		if(h->table[j].key == (char *) h->table) continue;
		
		i = i0;
		do {
			if(!newh->table[i].key) break;
			i = (i + 1) % newh->siz;
		} while(i != i0);
		newh->table[i] = h->table[j];
	}
	
	free(h->table);
	h->table = newh->table;
	h->siz = newh->siz;
	free(newh);
}

//Insert key-val pair, grows table if necessary
void ht_insert(hashtable *h, const char *k, void *v)
{
	int i;
	uint32_t hash = h->hash(k);
	const int i0 = hash % h->siz;
	
	i = i0;
	do {
		if(!h->table[i].key) break;
		if(h->table[i].key == (char *) h->table) break;
		if(!strcmp(h->table[i].key, k)){
			h->table[i].val = v;
			return;
		}
		
		i = (i + 1) % h->siz;
	} while(i != i0);
	
	if(h->table[i].key && h->table[i].key != (char *) h->table){
		ht_resize(h, h->siz * 2);
		ht_insert(h, k, v);
		return;
	}
	
	h->table[i].key = strdup(k);
	h->table[i].val = v;
	h->table[i].hash = hash;
	h->len++;
	
	//Relatively arbitrary limits
	if(h->len * 100 > h->siz * 70){
		ht_resize(h, h->siz * 2);
	}
	else if(h->len * 100 < h->siz * 10 && h->siz > 53){
		ht_resize(h, h->siz / 2);
	}
}

//Deletes a key
void ht_delete(hashtable *h, const char *k)
{
	int i;
	const int i0 = h->hash(k) % h->siz;
	
	i = i0;
	do {
		if(!h->table[i].key) return;
		if(h->table[i].key != (char *) h->table){
			if(!strcmp(h->table[i].key, k)){
				free(h->table[i].key);
				h->table[i].key = (char *) h->table;
				h->len--;
				return;
			}
		}
		i = (i + 1) % h->siz;
	} while(i != i0);
}

//105249 filenames
//find > list.h, then ^ -> " and $ -> ", plus const char *strings={, };
#include "list.h"

/*
Output:
0 done...
100 done...
200 done...
300 done...
400 done...
500 done...
600 done...
700 done...
800 done...
900 done...
Went through 11073732 strings
num_strings: 105249
Collisions:
DJB2		0
FNV1		3
*/

/*
gprof information (collision counting omitted):
Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls  us/call  us/call  name    
 29.01      3.01     3.01 44236788     0.07     0.07  fnv1
 26.12      5.72     2.71                             main
 25.83      8.40     2.68 44236788     0.06     0.06  djb2
 10.22      9.46     1.06 22138394     0.05     0.11  ht_insert
  3.95      9.87     0.41    36842    11.13    11.39  ht_resize
  3.57     10.24     0.37                             _mcount_private
  0.29     10.27     0.03                             __moddi3
  0.29     10.30     0.03                             free
  0.29     10.33     0.03                             strcmp
  0.19     10.35     0.02                             strdup
  0.14     10.37     0.01                             _fentry__
  0.10     10.38     0.01   246150     0.04     0.04  miller_rabin_test
*/

int main()
{
	char tmp[256];
	int i, j, k;
	int tot = 0;
	const int num_strings = sizeof(strings) / sizeof(strings[0]);
	
	srand(time(0));
	
	for(i = 0; i < 1000; i++){
		const int a = rand() % num_strings, b = rand() % num_strings;
		const int *min = (a < b) ? &a : &b, *max = (a > b) ? &a : &b;
		hashtable *h1, *h2;
		
		if(a == b) continue;
		
		h1 = ht_create(rand() % (num_strings / 1234));
		h2 = ht_create(rand() % (num_strings / 1234));
		
		h1->hash = djb2;
		h2->hash = fnv1;
		
		for(j = *min, k = 0; j < *max; j++, k++){
			ht_insert(h1, strings[j], (void *) strings[j]);
			ht_insert(h2, strings[j], (void *) k);
		}
		
		assert(h1->len == *max - *min);
		assert(h1->len == h2->len);
		
		for(j = *min, k = 0; j < *max; j++, k++){
			assert(ht_search(h1, strings[j]) == strings[j]);
			assert((int) ht_search(h2, strings[j]) == k);
		}
		
		for(j = *max - 1; j >= *min; j--){
			ht_delete(h1, strings[j]);
			ht_delete(h2, strings[j]);
			assert(!ht_search(h1, strings[j]));
			assert(!ht_search(h2, strings[j]));
			assert(h1->len == j - *min);
			assert(h2->len == j - *min);
		}
		
		for(j = 0; j < 20; j++){
			k = rand() % num_strings;
			ht_insert(h1, strings[k], (void *) strings[k]);
			ht_insert(h2, strings[k], (void *) k);
			assert(ht_search(h1, strings[k]) == strings[k]);
			assert((int) ht_search(h2, strings[k]) == k);
		}
		
		ht_destroy(h1);
		ht_destroy(h2);
		
		if(i % 100 == 0) printf("%d done...\n", i);
		
		tot += *max - *min;
	}
	
	printf("Went through %d strings\nnum_strings: %d\n", tot, num_strings);
	
	if(1){
		int dcoll = 0, fcoll = 0;
		hashtable *h1, *h2;
		h1 = ht_create((num_strings * 3) / 2);
		h2 = ht_create((num_strings * 3) / 2);
		h1->hash = djb2;
		h2->hash = fnv1;
		
		for(i = 0; i < num_strings; i++){
			sprintf(tmp, "%"PRIu32, djb2(strings[i]));
			if(ht_search(h1, tmp)) dcoll++;
			else ht_insert(h1, tmp, (void *) 1);
			
			sprintf(tmp, "%"PRIu32, fnv1(strings[i]));
			if(ht_search(h2, tmp)) fcoll++;
			else ht_insert(h2, tmp, (void *) 1);
		}
		
		printf("Collisions:\nDJB2\t\t%d\nFNV1\t\t%d\n", dcoll, fcoll);
	}
	
	return 0;
}