Question

Is there a straight-forward way to extend this rand() function (from K&R’s “The C Programming Language”) to yield 64 random bits instead of 15?

int rand()
{
  rand_next = rand_next * 1103515245 + 12345;
  return (unsigned int)(rand_next/ 65536) % 32768;
}

EDIT: And what I mean by that is changing it to use 64-bit numbers and different magic numbers. As opposed to throwing this in a for loop.

EDIT #2: This algorithm is effectively 15 bits of randomness, not 30. Stupid math mistake in my original post.

Answer 1

Linear congruential generators exist for any number of bits.

For 64 bits, MMIX (for example) uses the following recursive formula:

x = x * 6364136223846793005 + 1442695040888963407;