/* =========================================================================
 * jhash.c - Jenkins' Hash, maps from string to integer
 *
 * ========================================================================= 
 */

#include <string.h>
#include "jhash.h" 

// JenkinsHash - see header file for usage
unsigned long
JenkinsHash(const char *str, const unsigned long mod)
{
  if (str == NULL || mod <= 1) {
    return 0;
  }

  size_t len = strlen(str);
  unsigned long hash = 0;

  for (int i = 0; i < len; i++) {
    hash += str[i];
    hash += (hash << 10);
    hash ^= (hash >> 6);
  }

  hash += (hash << 3);
  hash ^= (hash >> 11);
  hash += (hash << 15);

  return (hash % mod);
}

#ifdef UNIT_TEST
#include <stdio.h>
#include "unittest.h"

int main()
{
  START_TEST_CASE("jhash");
  EXPECT(JenkinsHash(NULL, 1) == 0);
  EXPECT(JenkinsHash("", 1) == 0);
  EXPECT(JenkinsHash("CS50", 0) == 0);
  EXPECT(JenkinsHash("CS50", 1) == 0);
  EXPECT(JenkinsHash("CS50", 99999) == JenkinsHash("CS50", 99999));
  EXPECT(JenkinsHash("CS50", 99999) == 18704);
  EXPECT(JenkinsHash("This is a very long string and it will make it hard to read this test; fortunately, the function does not care.", 99999) == 86041);
  
  END_TEST_CASE;
  return TEST_RESULT;
}

#endif // UNIT_TEST