hashmap.c

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>

typedef struct Pair {
  struct Pair *next;
  const char *key;
  void *value;
} Pair;

typedef struct {
  Pair **pairs;
  size_t capacity;
} HashMap;

HashMap *newHashMap(size_t cap) {
  HashMap *map = malloc(sizeof(*map));
  map->capacity = cap;
  map->pairs = calloc(cap, sizeof(Pair *));

  return map;
}

void destroyHashMap(HashMap *map) {
  for (size_t i = 0; i < map->capacity; i++) {
    if (map->pairs[i] == NULL)
      continue;
    free(map->pairs[i]);
  }
  free(map->pairs);
  free(map);
}

size_t hashString(const char *s) {
  size_t hash = 1;
  for (size_t i = 0; i < strlen(s); i++) {
    size_t old = hash;
    hash *= s[i];
    hash ^= old;
  }

  return hash;
}

void insertHashMap(HashMap *map, const char *key, void *value) {
  size_t index = hashString(key) % map->capacity;
  Pair *pair = malloc(sizeof(*pair));
  *pair = (Pair){.next = NULL, .key = key, .value = value};

  if (map->pairs[index] == NULL) {
    map->pairs[index] = pair;
    return;
  }

  pair->next = map->pairs[index];
  map->pairs[index] = pair;
}

void *getHashMap(HashMap *map, const char *key) {
  size_t index = hashString(key) % map->capacity;

  if (map->pairs[index] == NULL) {
    return NULL;
  }

  Pair *p = map->pairs[index];
  while (strcmp(p->key, key)) {
    p = p->next;
    if (p == NULL) {
      return NULL;
    }
  }

  return p->value;
}

int main(int argc, char *argv[]) {
  HashMap *map = newHashMap(1024);

  insertHashMap(map, "asdf", "ASDF");
  insertHashMap(map, "leet", "1337");

  printf("asdf : %s\n", (char *)getHashMap(map, "asdf"));
  printf("leet : %s\n", (char *)getHashMap(map, "leet"));

  destroyHashMap(map);
  return 0;
}