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Re: random functions proposal [message #35159 is a reply to message #35158]

Tue, 17 January 2012 20:08

Sender Ghost
Messages: 301
Registered: November 2008

Senior Member

dolik.rce wrote on Tue, 17 January 2012 18:45

This pseudo scientific paper seems to propose reasonably simple algorithm that overcomes the obvious problems of the implementation Sender Ghost proposed.

Well, what I "proposed" (and I didn't propose, but just showed a simple solution) is useful for float numbers, not double, hence this Randomf, instead of Randomd, I think.
With qword Random64(qword n) it will be possible to do the same, of course.

mirek wrote on Tue, 17 January 2012 14:24

...but it looks like int64 -> double conversion is CPU opcode, so perhaps Random64(int n) as prerequisite, than Randomf() is a good path...

According to "Random number generators discussion" it is possible to combine two random dword values (MAKEQWORD macro might be useful here) to get random qword value.

qword Random64()
{
	return MAKEQWORD(Random(), Random());
}

qword Random64(qword n)
{
	qword mask = n, r;
	mask |= mask >> 1;	mask |= mask >> 2;
	mask |= mask >> 4;	mask |= mask >> 8;
	mask |= mask >> 16;	mask |= mask >> 32;

	do
		r = Random64() & mask;
	while(r >= n);
	return r;
}

qword Random64(qword a, qword b)
{
	if (a == b)
		return a;
	if (a < b)
		return a + Random64(b - a + 1);
	return b + Random64(a - b + 1);
}

Edit: Added possible Random64 implementation(s).

[Updated on: Tue, 17 January 2012 23:23]

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