CODEWITHSUNDEEP
algorithmtime
Tosh
Tosh

Reputation:

Convert timestamp to alphanum

I have an application where a user has to remember and insert an unix timestamp like 1221931027. In order to make it easier to remember the key I like to reduce the number of characters to insert through allowing the characters [a-z]. So I'm searching for an algorithm to convert the timestamp to a shorter alphanum version and do the same backwards. Any hints?

Upvotes: 1

Views: 1537

Answers (4)

Brian
Brian

Reputation: 119301

Another option sometimes used for things like this is to use lists of syllables. ie. you have a list of syllables like ['a','ab', 'ba','bi','bo','ca','...] and transform the number into base(len(list_of_syllables)). This is longer in terms of letters, but it can often be easier to memorise something like "flobagoka' than something like 'af3q5jl'. (The downside is that it can be easy to generate words that sound like profanity)

[Edit] Here's an example of such an algorithm. Using this, 1221931027 would be "buruvadrage"

Upvotes: 0

Thom Boyer
Thom Boyer

Reputation: 517

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

// tobase36() returns a pointer to static storage which is overwritten by 
// the next call to this function. 
//
// This implementation presumes ASCII or Latin1.

char * tobase36(time_t n)
{
  static char text[32];
  char *ptr = &text[sizeof(text)];
  *--ptr = 0; // NUL terminator

  // handle special case of n==0
  if (n==0) {
    *--ptr = '0';
    return ptr;
  }

  // some systems don't support negative time values, but some do
  int isNegative = 0;
  if (n < 0)
  {
    isNegative = 1;
    n = -n;
  }

  // this loop is the heart of the conversion
  while (n != 0)
  {
    int digit = n % 36;
    n /= 36;
    *--ptr = digit + (digit < 10 ? '0' : 'A'-10);
  }

  // insert '-' if needed
  if (isNegative)
  {
    *--ptr = '-';
  }

  return ptr;
}

int main(int argc, const char **argv)
{
  int i;
  for (i=1; i<argc; ++i)
  {
    long timestamp = atol(argv[i]);
    printf("%12d => %8s\n", timestamp, tobase36(timestamp));
  }
}

/*
$ gcc -o base36 base36.c
$ ./base36 0 1 -1 10 11 20 30 35 36 71 72 2147483647 -2147483647
           0 =>        0
           1 =>        1
          -1 =>       -1
          10 =>        A
          11 =>        B
          20 =>        K
          30 =>        U
          35 =>        Z
          36 =>       10
          71 =>       1Z
          72 =>       20
  2147483647 =>   ZIK0ZJ
 -2147483647 =>  -ZIK0ZJ
*/

Upvotes: 2

Stephen Wrighton
Stephen Wrighton

Reputation: 37850

convert the timestamp to HEX. That will generate a shorter alphanumeric number for you out of the timestamp.

Upvotes: 0

Noether
Noether

Reputation: 199

You could just convert the timestamp into base-36.

Upvotes: 5

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