I see in FIXES: "Fix incorrect divisor in rand() - it was returning even random numbers only."

I don't understand about even random numbers from awk rand(); rand() returns "a floating point pseudo-random number n, such that 0<=n<1." (posix). How can a fraction be even or odd?

The fix changed (Awkfloat) random() / (0x7fffffffL + 0x1UL) to (Awkfloat) random() / RAND_MAX. There are a couple problems here.

random() returns a max value of 2**31-1; if you divide (Awkfloat)random() by RAND_MAX (equals 2**31-1 in my gcc), the result can range up to (and including) 1, but awk rand() is supposed to be less than 1. Which is why the original code divided by (0x7fffffffL + 0x1UL), i.e. 2**31.

RAND_MAX happens to be 2**31-1 on some C implementations, but ISO C and POSIX say RAND_MAX is "Maximum value returned by rand(); at least 32767." So RAND_MAX has nothing to do with random() and need not be 2**31-1.

What was the actual problem that prompted the change?