RERand - 100% correct GML runtime RNG implementation.... in pure GML!

rerand.gml

function rerand() constructor {
	state = [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ];
	g_nRandSeed = 0;
	g_RndIndex = 0;
	s_nRandomPoly = $DA442D24;
	RND_MAX = $FFFFFFFF;
	s_nStateAndMask = RND_MAX;

	InitRandom = function(/*uint*/ _seed) {
		var uVar3 = _seed;
		g_nRandSeed = _seed;
		for (var iVar1 = 0; iVar1 < 16; ++iVar1) {
			// legacy GM does 7FFFFFFF for some reason...
			uVar3 = ((((((uVar3 * 0x343fd) & RND_MAX) + 0x269ec3 & RND_MAX) >> 0x10) & RND_MAX)) & s_nStateAndMask;
			state[@ iVar1] = uVar3;
		}
		g_RndIndex = 0;
		return _seed;
	};

	YYRandom = function()
	{
	    var uVar1 = ((state[g_RndIndex & RND_MAX] & RND_MAX) ^ (state[((g_RndIndex + 0xd) & RND_MAX) & 0xf] & RND_MAX)) & RND_MAX;
	    var uVar2 = uVar1 ^ ((state[g_RndIndex & RND_MAX] << 0x10) & RND_MAX) ^ ((state[((g_RndIndex + 0xd) & RND_MAX) & 0xf] << 0xf) & RND_MAX);
	    var uVar3 = (state[((g_RndIndex + 9) & RND_MAX) & 0xf] & RND_MAX) ^ ((state[((g_RndIndex + 9) & RND_MAX) & 0xf] >> 0xb) & RND_MAX);
	    var uVar4 = ((uVar2 & RND_MAX) ^ (uVar3 & RND_MAX)) & RND_MAX;
	    state[g_RndIndex & RND_MAX] = uVar4 & RND_MAX;
	    g_RndIndex = (((g_RndIndex - 1) & RND_MAX) & 0xf) & RND_MAX;
		// don't try to understand lol
	    state[g_RndIndex] =
	        (state[g_RndIndex] ^ ((uVar2 ^ ((((uVar4 ^ ((s_nRandomPoly & ((uVar4 << 5) & RND_MAX) & RND_MAX))) & RND_MAX) ^ ((state[g_RndIndex] << 2) & RND_MAX)) & RND_MAX) ^
			((uVar1 << 0x12) & RND_MAX) ^ ((uVar3 << 0x1c) & RND_MAX)) & RND_MAX)) & RND_MAX;
	    return state[g_RndIndex];
	};

	YYRandomRange = function(_range)
	{
	    var uVar1;
	    var uVar2;
	    var uVar3;

		_range = floor(_range);
	    uVar2 = YYRandom();
	    uVar3 = abs(_range);
	    uVar1 = 0;
	    if (uVar3 != 0) {
	        uVar1 = uVar2 div uVar3;
	    }
	    return uVar2 - uVar1 * uVar3;
	};

	ChangeToOldPoly = function(bUseOldPoly)
	{
	    if (!bUseOldPoly) {
	        s_nRandomPoly = 0xda442d24;
			s_nStateAndMask = RND_MAX;
	        return;
	    }
	    s_nRandomPoly = 0xda442d20;
		s_nStateAndMask = $7FFFFFFF;
	};

	fYYRandom = function(_range)
	{
	    var uVar1;
	    var local_18;

	    if (_range == 1.0) {
	        uVar1 = YYRandom();
	        local_18 = uVar1 / 4294967296.0;
	    }
	    else {
	        uVar1 = YYRandom();
	        local_18 = (uVar1 / 4294967296.0) * _range;
	    }
	    return local_18;
	};

	/* Function_Math.cpp:1425
	   DWARF DIE: 3e7a97 */
	F_Random = function(argument0)
	{
	    var dVar1;
	    var dVar2;

	    dVar1 = fYYRandom(1.0);
	    dVar2 = argument0;
	    return dVar1 * dVar2;
	};

	/* Function_Math.cpp:1436
	   DWARF DIE: 3e7b3a */
	F_RandomRange = function(argument0, argument1)
	{
	    var dVar1;
	    var dVar2;
	    var dVar3;

	    dVar1 = argument0;
	    dVar2 = argument1;
	    /* Begin: inline double YYGML_random_range(double _base, double _end) */
	    dVar3 = dVar2 - dVar1;
	    if (dVar2 <= dVar1) {
	        dVar3 = dVar1 - dVar2;
	        dVar1 = dVar2;
	    }
	    dVar2 = fYYRandom(1.0);
	    return dVar1 + dVar2 * dVar3;
	};

	/* Function_Math.cpp:1535
	   DWARF DIE: 68dad6 */
	F_RandomGetSeed = function()
	{
	    return g_nRandSeed;
	};

	/* Function_Math.cpp:1512
	   DWARF DIE: 68da1f */
	F_RandomSetSeed = function(argument0)
	{
	    var _seed;
	    _seed = floor(argument0) & RND_MAX;
	    return InitRandom(_seed);
	};

	iScript_Random = function(_range)
	{
	    var lVar1;
	    var lVar2;
	    var uVar3;
	    var uVar4;
	    var lVar5;

		_range = int64(_range);
	    uVar3 = int64(YYRandom());
	    uVar4 = int64(YYRandom());
	    uVar3 = int64((uVar3 & 0xffffffff) | ((uVar4 & 0x7fffffff) << 0x20));
	    lVar1 = int64(-1);
	    if (int64(-1) < _range) {
	        lVar1 = int64(1);
	    }
	    lVar5 = int64(lVar1 * _range);
	    lVar2 = int64(0);
	    if (lVar5 != int64(0)) {
	        lVar2 = int64(uVar3 / lVar5);
	    }
	    return int64(int64(int64(uVar3) - int64(lVar2) * int64(lVar5)) * int64(lVar1));
	};

	/* Function_Math.cpp:1468
	   DWARF DIE: 68d764 */
	F_IRandom = function(argument0)
	{
	    var iVar6 = int64(floor(argument0));
	    var lVar2 = int64(-1);
	    if (int64(-1) < int64(iVar6)) {
	        lVar2 = int64(1);
	    }
	    return real(int64(iScript_Random(int64(int64(lVar2) + int64(iVar6)))));
	};

	/* Function_Math.cpp:1482
	   DWARF DIE: 68d8ee */
	F_IRandomRange = function(argument0, argument1)
	{
	    var lVar6 = int64(floor(argument0));
	    var iVar7 = int64(floor(argument1));
	    var lVar3 = int64(int64(iVar7) - int64(lVar6));
	    if (iVar7 <= lVar6) {
	        lVar3 = int64(lVar6 - iVar7);
	        lVar6 = int64(iVar7);
	    }
	    return real(int64(lVar6) + int64(iScript_Random(int64(lVar3 + 1))));
	};

	/* Function_Math.cpp:2277
	   DWARF DIE: 3e9a34 */
	F_Choose = function()
	{
		var _argc = argument_count;
		if (_argc != 0)
		{
			return argument[floor(YYRandomRange(_argc))];
		}
	
		return 0;
	};
	
	F_RandomUseOldVersion = function(doUse)
	{
		// might not be correct???
		ChangeToOldPoly(doUse);
	};
	
	g_nRandSeed = InitRandom(0);
}

/* -- TESTCASE BEGIN, CUT THIS OFF IF YOU DON'T NEED IT -- */
var r = new rerand();

var s = 0;
repeat (10000) {
	random_set_seed(s);
	r.F_RandomSetSeed(s);
	
	repeat (100) {
		if (r.F_Random(10) != random(10)) {
			throw "random() fail!";
		}
	
		if (r.F_RandomRange(10, 100) != random_range(10, 100)) {
			throw "random_range() fail!";
		}
	
		if (r.F_IRandom(100) != irandom(100)) {
			throw "irandom() fail!";
		}
	
		if (r.F_IRandomRange(10, 100) != irandom_range(10, 100)) {
			throw "irandom_range() fail!";
		}
	
		if (r.F_Choose(1, 2, 3) != choose(1, 2, 3)) {
			throw "choose() fail!";
		}
	}
	
	++s;
}

show_message("Testcase PASS!");