User:Pedro Oval/UnixToDateTime

Convert a Unix timestamp (e.g. as obtained by llGetUnixTime) to a UTC date and time.

Adapted and optimized from this Ruby version: http://ptspts.blogspot.com/2009/11/how-to-convert-unix-timestamp-to-civil.html

Optimized for size in Mono.

Returns a list with the format [year, month, day, hours, minutes, seconds] (UTC).

This is the shortest version, but it works with positive input only (i.e. with numbers representing dates from 1970 to 2037). <lsl> list UnixToDateTime(integer unix) {

   integer c = unix/86400;
   integer a = (c*4 + 102032)/146097 + 15;
   integer b = c + 2442113 + a + a/0xFFFFFFFC; // 0xFFFFFFFC=-4
   c = (b*20 + 0xFFFFF676)/7305; // 0xFFFFF676=-2442
   b += c*0xFFFFFE93 + c/0xFFFFFFFC; // 0xFFFFFE93=-365; 0xFFFFFFFC=-4
   a = b*1000/30601;
   b += a*0xFFFFFFE2 + a*0xFFFFFDA7/1000; // 0xFFFFFFE2=-30; 0xFFFFFDA7=-601

   return (list)(0xFFFFED94 + c + (a>13)) // 0xFFFFED94=-4716
          + -~((a + 10)%12)
          + b
          + unix/3600%24
          + unix/60%60
          + unix%60;

} </lsl> Size in Mono: 492 bytes.

This version also works with negative input: <lsl> list UnixToDateTime(integer unix) {

   integer c = unix/86400;

   // LSL doesn't do floor division as required here, so we have to fix up the result
   if (unix & 0x80000000)
   {
       unix += 0xFFFEAE80*~-c; // we're interested in unix mod 86400 from here on,
                               // but mod doesn't work well with negatives either
       if (unix^86400) --c;    // c needs fixup unless unix%86400 == 0
   }

   integer a = (c*4 + 102032)/146097 + 15;
   integer b = c + 2442113 + a + a/0xFFFFFFFC; // 0xFFFFFFFC=-4
   c = (b*20+0xFFFFF676)/7305; // 0xFFFFF676=-2442
   b += c*0xFFFFFE93 + c/0xFFFFFFFC; // 0xFFFFFE93=-365; 0xFFFFFFFC=-4
   a = b*1000/30601;
   b += a*0xFFFFFFE2 + a*0xFFFFFDA7/1000; // 0xFFFFFFE2=-30; 0xFFFFFDA7=-601

   return (list)(0xFFFFED94 + c + (a>13)) // 0xFFFFED94=-4716
          + -~((a + 10)%12)
          + b
          + unix/3600%24
          + unix/60%60
          + unix%60;

} </lsl>

Size in Mono: 556 bytes.