--XRNG - SRB2 Lua implementation of xoshiro128++ PRNG with multiple instance support, made by Nightwolf
--The original xoshiro128++ code can be found here: https://prng.di.unimi.it/xoshiro128plusplus.c

--XRNG Version: v1

--Main xoshiro128++ function, generates a random value based on the RNG state (s) and modifies the state
--The name was changed from 'next' because a standard lua function uses that name
local function generate(s)
	local x = s[1] + s[4]
	local result = ((x << 7) | (x >> 25)) + s[1]

	local t = s[2] << 9

	s[3] = $ ^^ s[1]
	s[4] = $ ^^ s[2]
	s[2] = $ ^^ s[3]
	s[1] = $ ^^ s[4]

	s[3] = $ ^^ t

	s[4] = (s[4] << 11) | (s[4] >> 21)

	return result
end

--This function is equivalent to 2^64 calls to generate(). In XRNG it's used to initialize the RNG state after seeding it
local function jump(s)
	local JUMP = { 0x8764000b, 0xf542d2d3, 0x6fa035c3, 0x77f2db5b }
	
	local s1 = 0
	local s2 = 0
	local s3 = 0
	local s4 = 0
	for i = 1,#JUMP do
		for b = 0,31 do
			if JUMP[i] & (1 << b) then
				s1 = $ ^^ s[1]
				s2 = $ ^^ s[2]
				s3 = $ ^^ s[3]
				s4 = $ ^^ s[4]
			end
			generate(s)
		end
	end
	
	s[1] = s1
	s[2] = s2
	s[3] = s3
	s[4] = s4
end

--XRNG interface functions start here

--This function sets the RNG seed and returns it (as a number)
local function xrng_setSeed(self,seed)
	seed = seed or 0
	if type(seed) == "string" then
		local hash = 0
		for i = 1,string.len(seed) do
			hash = 31*$+string.byte(seed,i)
		end
		seed = hash
	elseif type(seed) ~= "number" then
		error("xrng_setSeed: incorrect variable type in 'seed' argument (expected number, string or nil)")
	end
	self.s[1],self.s[2],self.s[3],self.s[4] = seed,135478321,0,0
	jump(self.s)
	return seed
end

--This function returns a random integer, generate() function wrapper
local function xrng_randomSigned(self)
	return generate(self.s)
end

--This function returns a random non-negative integer
local function xrng_randomUnsigned(self)
	return generate(self.s) >> 1
end

--This function returns a random integer between 0 and 65535 (FRACUNIT-1)
local function xrng_randomFixed(self)
	return generate(self.s) >> 16
end

--This function returns a random integer between 0 and 255
local function xrng_randomByte(self)
	return generate(self.s) >> 24
end

--This function returns a random integer between 1 and a, made for accessing a random element in Lua arrays
local function xrng_randomKey(self,a)
	return ((generate(self.s) >> 1) % a) + 1
end

--This function returns a random integer between a and b - the difference should not be bigger than INT32_MAX (2147483647)
local function xrng_randomRange(self,a,b)
	a = a or 0
	b = b or 0
	if a > b then a,b = b,a end
	local range = (b-a+1)
	local result = generate(self.s) >> 1
	return (result % (range or 1)) + a
end

--This function returns true p% of the time (0 is 0%, FRACUNIT/2 is 50%, FRACUNIT is 100%, etc.)
local function xrng_randomChance(self,p)
	p = $ or 0
	local result = generate(self.s) >> 16
	return result < p
end

--This function creates a new RNG instance (if seed value is present, the RNG is seeded with it)
--Returns the RNG instance and the RNG seed
local function xrng_new(seed)
	local newrng = {}
	newrng.s = {0,0,0,0}
	newrng.setSeed = xrng_setSeed
	newrng.randomNumber = xrng_randomSigned
	newrng.randomUnsigned = xrng_randomUnsigned
	newrng.randomFixed = xrng_randomFixed
	newrng.randomByte = xrng_randomByte
	newrng.randomKey = xrng_randomKey
	newrng.randomRange = xrng_randomRange
	newrng.randomChance = xrng_randomChance
	
	local seed = xrng_setSeed(newrng,seed)

	return newrng,seed
end

rawset(_G,"newXRNG",xrng_new)