From e824e9023f078da0051c54c29aaacf23eb6a6e95 Mon Sep 17 00:00:00 2001
From: sfan5 <sfan5@live.de>
Date: Wed, 10 Jan 2024 20:08:00 +0100
Subject: [PATCH] Simplify LuaPseudoRandom::l_next and fix docs

Also extends the allowed range on the C++ side. This has no side-effects.
---
 doc/lua_api.md                        | 11 +++++++----
 games/devtest/mods/unittests/misc.lua |  2 ++
 src/noise.h                           |  2 +-
 src/script/lua_api/l_noise.cpp        | 25 +++++++++++--------------
 src/unittest/test_random.cpp          |  2 +-
 5 files changed, 22 insertions(+), 20 deletions(-)

diff --git a/doc/lua_api.md b/doc/lua_api.md
index c4e1265c5..8afe2b78d 100644
--- a/doc/lua_api.md
+++ b/doc/lua_api.md
@@ -8061,7 +8061,9 @@ A 32-bit pseudorandom number generator.
 Uses PCG32, an algorithm of the permuted congruential generator family,
 offering very strong randomness.
 
-It can be created via `PcgRandom(seed)` or `PcgRandom(seed, sequence)`.
+* constructor `PcgRandom(seed, [seq])`
+  * `seed`: 64-bit unsigned seed
+  * `seq`: 64-bit unsigned sequence, optional
 
 ### Methods
 
@@ -8156,14 +8158,15 @@ Can be obtained using `player:get_meta()`.
 A 16-bit pseudorandom number generator.
 Uses a well-known LCG algorithm introduced by K&R.
 
-It can be created via `PseudoRandom(seed)`.
+* constructor `PseudoRandom(seed)`
+  * `seed`: 32-bit signed number
 
 ### Methods
 
 * `next()`: return next integer random number [`0`...`32767`]
 * `next(min, max)`: return next integer random number [`min`...`max`]
-    * `((max - min) == 32767) or ((max-min) <= 6553))` must be true
-      due to the simple implementation making bad distribution otherwise.
+    * Either `max - min == 32767` or `max - min <= 6553` must be true
+      due to the simple implementation making a bad distribution otherwise.
 
 `Raycast`
 ---------
diff --git a/games/devtest/mods/unittests/misc.lua b/games/devtest/mods/unittests/misc.lua
index fd6c0a058..e96103319 100644
--- a/games/devtest/mods/unittests/misc.lua
+++ b/games/devtest/mods/unittests/misc.lua
@@ -6,6 +6,8 @@ local function test_random()
 
 	local pr2 = PseudoRandom(-101)
 	assert(pr2:next(0, 100) == 35)
+	-- unusual case that is normally disallowed:
+	assert(pr2:next(10000, 42767) == 12485)
 end
 unittests.register("test_random", test_random)
 
diff --git a/src/noise.h b/src/noise.h
index 6c17afd68..d9b7a6521 100644
--- a/src/noise.h
+++ b/src/noise.h
@@ -70,7 +70,7 @@ public:
 		PcgRandom, we cannot modify this RNG's range as it would change the
 		output of this RNG for reverse compatibility.
 		*/
-		if ((u32)(max - min) > (RANDOM_RANGE + 1) / 10)
+		if ((u32)(max - min) > (RANDOM_RANGE + 1) / 5)
 			throw PrngException("Range too large");
 
 		return (next() % (max - min + 1)) + min;
diff --git a/src/script/lua_api/l_noise.cpp b/src/script/lua_api/l_noise.cpp
index 16eb1de43..03f78c960 100644
--- a/src/script/lua_api/l_noise.cpp
+++ b/src/script/lua_api/l_noise.cpp
@@ -405,25 +405,22 @@ int LuaPseudoRandom::l_next(lua_State *L)
 	NO_MAP_LOCK_REQUIRED;
 
 	LuaPseudoRandom *o = checkObject<LuaPseudoRandom>(L, 1);
-	int min = 0;
-	int max = 32767;
-	lua_settop(L, 3);
+	int min = 0, max = PseudoRandom::RANDOM_RANGE;
 	if (lua_isnumber(L, 2))
 		min = luaL_checkinteger(L, 2);
 	if (lua_isnumber(L, 3))
 		max = luaL_checkinteger(L, 3);
-	if (max < min) {
-		errorstream<<"PseudoRandom.next(): max="<<max<<" min="<<min<<std::endl;
-		throw LuaError("PseudoRandom.next(): max < min");
+
+	int val;
+	if (max - min == PseudoRandom::RANDOM_RANGE) {
+		val = o->m_pseudo.next() + min;
+	} else {
+		try {
+			val = o->m_pseudo.range(min, max);
+		} catch (PrngException &e) {
+			throw LuaError(e.what());
+		}
 	}
-	if(max - min != 32767 && max - min > 32767/5)
-		throw LuaError("PseudoRandom.next() max-min is not 32767"
-				" and is > 32768/5. This is disallowed due to"
-				" the bad random distribution the"
-				" implementation would otherwise make.");
-	PseudoRandom &pseudo = o->m_pseudo;
-	int val = pseudo.next();
-	val = (val % (max-min+1)) + min;
 	lua_pushinteger(L, val);
 	return 1;
 }
diff --git a/src/unittest/test_random.cpp b/src/unittest/test_random.cpp
index 9dd88d07e..5b9bbddcf 100644
--- a/src/unittest/test_random.cpp
+++ b/src/unittest/test_random.cpp
@@ -81,7 +81,7 @@ void TestRandom::testPseudoRandomRange()
 {
 	PseudoRandom pr((int)time(NULL));
 
-	EXCEPTION_CHECK(PrngException, pr.range(2000, 6000));
+	EXCEPTION_CHECK(PrngException, pr.range(2000, 8600));
 	EXCEPTION_CHECK(PrngException, pr.range(5, 1));
 
 	for (u32 i = 0; i != 32768; i++) {