KataFilter/bfilter.c

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <fnv.h>
#include "bfilter.h"

int
printbits(uint32_t n, size_t c) {
  uint32_t i = c-1;
  while (n >= 2) {
    printf("%d", n & 1);
    i--;
    n >>= 1;
  }
  printf("%d", n & 1);
  return 0;
}

int
print_barray(bit_array_t *arr) {
  for(uint32_t i = 0; i < arr->num_ints; i++) {
    printbits(arr->arr[i], arr->num_elems/arr->num_ints);
  }
  printf("\n");
  return 0;
}

bit_array_t*
empty_bfilter(int size) {
  int width = (size/32) + 1; // 32 for a 32 bit int

  uint32_t *barray = calloc(width, sizeof (int));

  bit_array_t *result = calloc(1, sizeof (bit_array_t));

  result->arr = barray;
  result->num_ints = width;
  result->num_elems = width*32;

  return result;
}

int
setbit(bit_array_t *arr, int k) {
  if ((uint32_t)k >= arr->num_elems) {
    printf("Tried to set a bit beyond the current limit, limit = %zu, k = %d\nExiting...\n",
           arr->num_elems, k);
    exit(1);
  }
  /* The position in the int we're looking at */
  int i = k/32;

  /* The position of the int in the array */
  int pos = k % 32;

  unsigned int flag = 1;

  /* Shift the flag to the position of the bit we want to set */
  flag = flag << pos;

  arr->arr[i] = arr->arr[i] | flag;

  return 0;
}

int
unsetbit(bit_array_t *arr, int k) {
  if ((uint32_t)k >= arr->num_elems) {
    printf("Tried to set a bit beyond the current limit, limit = %zu, k = %d\nExiting...\n",
           arr->num_elems, k);
    exit(1);
  }
  int i = k/32;

  int pos = k % 32;

  unsigned int flag = 1;

  flag = ~(flag << pos);

  arr->arr[i] = arr->arr[i] & flag;

  return 0;
}

int
getbit(bit_array_t *arr, int k) {
  int i = k/32;
  int pos = k % 32;
  unsigned int flag = 1;

  flag = flag << pos;

  if (arr->arr[i] & flag) {
    // k-th bit is 1
    return 1;
  }
  else {
    // k-th bit is 0
    return 0;
  }
}

fnv_hashes_t
hash_fnv(const char* value) {
  uint64_t hval;

  fnv_hashes_t hashes;

  fnv64Init(&hval);

  fnv64UpdateBuffer(&hval, value, strlen(value));

  uint32_t n_0 = hval >> 32;
  uint32_t n_1 = hval & 0x00000000ffffffff;

  hashes.hash_1 = n_0;
  hashes.hash_2 = n_1;

  return hashes;
}

uint32_t
kth_hash(fnv_hashes_t hashes,
         uint32_t i,
         size_t m) {
  return (hashes.hash_1 + hashes.hash_2 * i) % m;
}

hashes_t
hash(const char *input, uint32_t k, size_t m) {
  fnv_hashes_t fnv = hash_fnv(input);

  if (k <= 2) {
    hashes_t hashes = calloc(2, sizeof (uint32_t));
    hashes[0] = fnv.hash_1 % m;
    hashes[1] = fnv.hash_2 % m;
    return hashes;
  }

  hashes_t hashes = calloc(k, sizeof (uint32_t));

  hashes[0] = fnv.hash_1 % m;
  hashes[1] = fnv.hash_2 % m;

  for(uint32_t i = 0; i < (k-2); i++) {
    hashes[i+2] = kth_hash(fnv, i+2, m);
  }
  return hashes;
}

int
bfilter_set(bit_array_t *filter,
            const char *key,
            int k) {
  if (k <= 2) {
    k = 2;
  }
  hashes_t hashes = hash(key, k, filter->num_elems);

  for(int i = 0; i < k; i++) {
    setbit(filter, hashes[i]);
  }
  free(hashes);
  return 0;
}

int
bfilter_get(bit_array_t *filter,
            const char*key,
            int k) {
  if (k <= 2) {
    k = 2;
  }
  hashes_t hashes = hash(key, k, filter->num_elems);

  int exists = 1;

  for(int i = 0; i < k; i++) {
    if (!getbit(filter, hashes[i])) {
      exists = 0;
    }
  }
  free(hashes);
  return exists;
}

int
release_bfilter(bit_array_t *filter) {
  free(filter->arr);
  free(filter);
  return 0;
}