Problem - Kevin Tafuro

Discussion
Do not use this solution for getting random floating-point values; it
will not produce numbers in a uniform distribution because of the
mechanics of floating-point formats.
To get a random integer value, all you need to do is fill the bytes of the integer with
random data. You can do this by casting a pointer to an integer to a binary string,
then passing it on to a function that fills a buffer with random bytes. For example,
use the following function to get a random unsigned integer, using the spc_rand( )
interface defined in Recipe 11.2:
unsigned int spc_rand_uint(void) {
unsigned int res;
spc_rand((unsigned char *)&res, sizeof(unsigned int));
return res;
}
This solution can easily be adapted to other integer data types simply by changing all
the instances of unsigned int to the appropriate type.
See Also
Recipe 11.2
11.11 Getting a Random Integer in a Range
Problem
You want to choose a number in a particular range, with each possible value equally
likely. For example, you may be simulating dice rolling and do not want any number
to be more likely to come up than any other. You want all numbers in the range to be
possible values, including both endpoints. That is, if you ask for a number between 1
and 6, you’d like both 1 and 6 to be as likely as 2, 3, 4, or 5.
Solution
There are multiple ways to handle this problem. The most common is the least correct,
and that is to simply reduce a random integer (see Recipe 11.10) modulo the
size of the range and add to the minimum possible value. This can lead to slight
biases in your random numbers, which can sometimes lead to practical attacks,
because it means that some outputs are more likely than others.
We discuss more exact solutions in the next section.
606 | Chapter 11: Random Numbers
This is the Title of the Book, eMatter Edition
Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.