[MIRROR] Prevents NAN amounts infecting the chemistry reagent container system [MDB IGNORE] (#15482)

* Prevents NAN amounts infecting the chemistry reagent container system (#69017)

* Don't allow NAN into the reagent holders, and better reporting on add reagent and remove reagent

* Replace admin message with stack_trace and return and improve math defines to check for finite numbers

* Refactor things to use these new defines, attempts to fix unit tests by filtering out <= 0 amounts first

Co-authored-by: Aleksej Komarov <stylemistake@ gmail.com>

* Prevents NAN amounts infecting the chemistry reagent container system

Co-authored-by: oranges <email@oranges.net.nz>
Co-authored-by: Aleksej Komarov <stylemistake@ gmail.com>

code/__DEFINES/maths.dm

@@ -1,7 +1,13 @@
 // Remove these once we have Byond implementation.
-#define ISNAN(a) (a!=a)
-#define ISINF(a) (!ISNAN(a) && ISNAN(a-a))
-#define IS_INF_OR_NAN(a) (ISNAN(a-a))
+// ------------------------------------
+#define IS_NAN(a) (a!=a)
+
+#define IS_INF__UNSAFE(a) (a==a && a-a!=a-a)
+#define IS_INF(a) (isnum(a) && IS_INF__UNSAFE(a))
+
+#define IS_FINITE__UNSAFE(a) (a-a==a-a)
+#define IS_FINITE(a) (isnum(a) && IS_FINITE__UNSAFE(a))
+// ------------------------------------
 // Aight dont remove the rest
 
 // Credits to Nickr5 for the useful procs I've taken from his library resource.
@@ -104,7 +110,7 @@
 	. = list()
 	var/d = b*b - 4 * a * c
 	var/bottom  = 2 * a
-	if(d < 0 || IS_INF_OR_NAN(d) || IS_INF_OR_NAN(bottom))
+	if(d < 0 || !IS_FINITE__UNSAFE(d) || !IS_FINITE__UNSAFE(bottom))
 		return
 	var/root = sqrt(d)
 	. += (-b + root) / bottom

code/game/machinery/autolathe.dm

@@ -174,8 +174,8 @@
 				return
 
 			var/multiplier = text2num(params["multiplier"])
-			if(!multiplier)
-				to_chat(usr, span_alert("[src] only accepts a numerical multiplier!"))
+			if(!multiplier || !IS_FINITE(multiplier))
+				stack_trace("Invalid multiplier value in stack creation [multiplier], [usr] is likely attempting an exploit")
 				return
 			var/is_stack = ispath(being_built.build_path, /obj/item/stack)
 			multiplier = clamp(round(multiplier),1,50)

code/game/objects/items/stacks/stack.dm

@@ -357,7 +357,8 @@
 		return
 	if(!is_valid_recipe(recipe, recipes)) //href exploit protection
 		return
-	if(!multiplier || multiplier < 1) //href exploit protection
+	if(!multiplier || multiplier < 1 || !IS_FINITE(multiplier)) //href exploit protection
+		stack_trace("Invalid multiplier value in stack creation [multiplier], [usr] is likely attempting an exploit")
 		return
 	if(!building_checks(builder, recipe, multiplier))
 		return

code/modules/atmospherics/gasmixtures/gas_mixture.dm

@@ -659,7 +659,7 @@ GLOBAL_LIST_INIT(gaslist_cache, init_gaslist_cache())
 /// Do mind that the numbers can get very big and might hit BYOND's single point float limit.
 /datum/gas_mixture/proc/gas_pressure_quadratic(a, b, c, lower_limit, upper_limit)
 	var/solution
-	if(!IS_INF_OR_NAN(a) && !IS_INF_OR_NAN(b) && !IS_INF_OR_NAN(c))
+	if(IS_FINITE(a) && IS_FINITE(b) && IS_FINITE(c))
 		solution = max(SolveQuadratic(a, b, c))
 		if(solution > lower_limit && solution < upper_limit) //SolveQuadratic can return empty lists so be careful here
 			return solution
@@ -670,7 +670,7 @@ GLOBAL_LIST_INIT(gaslist_cache, init_gaslist_cache())
 /// We use the slope of an approximate value to get closer to the root of a given equation.
 /datum/gas_mixture/proc/gas_pressure_approximate(a, b, c, lower_limit, upper_limit)
 	var/solution
-	if(!IS_INF_OR_NAN(a) && !IS_INF_OR_NAN(b) && !IS_INF_OR_NAN(c))
+	if(IS_FINITE(a) && IS_FINITE(b) && IS_FINITE(c))
 		// We start at the extrema of the equation, added by a number.
 		// This way we will hopefully always converge on the positive root, while starting at a reasonable number.
 		solution = (-b / (2 * a)) + 200

code/modules/reagents/chemistry/holder.dm

@@ -163,10 +163,12 @@
  * * ignore splitting - Don't call the process that handles reagent spliting in a mob (impure/inverse) - generally leave this false unless you care about REAGENTS_DONOTSPLIT flags (see reagent defines)
  */
 /datum/reagents/proc/add_reagent(reagent, amount, list/data=null, reagtemp = DEFAULT_REAGENT_TEMPERATURE, added_purity = null, added_ph, no_react = FALSE, override_base_ph = FALSE, ignore_splitting = FALSE)
-	if(!isnum(amount) || !amount)
+	// Prevents small amount problems, as well as zero and below zero amounts.
+	if(amount <= CHEMICAL_QUANTISATION_LEVEL)
 		return FALSE
 
-	if(amount <= CHEMICAL_QUANTISATION_LEVEL)//To prevent small amount problems.
+	if(!IS_FINITE(amount))
+		stack_trace("non finite amount passed to add reagent [amount] [reagent]")
 		return FALSE
 
 	if(SEND_SIGNAL(src, COMSIG_REAGENTS_PRE_ADD_REAGENT, reagent, amount, reagtemp, data, no_react) & COMPONENT_CANCEL_REAGENT_ADD)
@@ -277,13 +279,11 @@
 /// Remove a specific reagent
 /datum/reagents/proc/remove_reagent(reagent, amount, safety = TRUE, no_react = FALSE)//Added a safety check for the trans_id_to
 	if(isnull(amount))
-		amount = 0
-		CRASH("null amount passed to reagent code")
-
-	if(!isnum(amount))
+		stack_trace("null amount passed to reagent code")
 		return FALSE
 
-	if(amount < 0)
+	if(amount < 0 || !IS_FINITE(amount))
+		stack_trace("invalid number passed to remove_reagent [amount]")
 		return FALSE
 
 	var/list/cached_reagents = reagent_list