From 896af463abaf61586a30a4f95f034fe2ddc1e4da Mon Sep 17 00:00:00 2001
From: UnknownShadow200 <unknownshadow200@gmail.com>
Date: Wed, 23 Oct 2024 21:30:57 +1100
Subject: [PATCH] Pure classic mode: Don't allow chat scrolling

---
 src/Game.c      |  2 ++
 src/Generator.c | 21 +++++++++++----------
 src/Screens.c   |  1 +
 3 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/src/Game.c b/src/Game.c
index 028f7e668..81ed15534 100644
--- a/src/Game.c
+++ b/src/Game.c
@@ -640,6 +640,8 @@ static CC_INLINE float ElapsedMilliseconds(cc_uint64 beg, cc_uint64 end) {
 	cc_uint64 elapsed = Stopwatch_ElapsedMicroseconds(beg, end);
 	if (elapsed > 5000000) elapsed = 5000000;
 	
+	/* Avoid uint64 / float division, as that typically gets implemented */
+	/* using a library function rather than a direct CPU instruction */
 	return (int)elapsed / 1000.0f;
 }
 
diff --git a/src/Generator.c b/src/Generator.c
index b3ccfed3d..f0bfc4a23 100644
--- a/src/Generator.c
+++ b/src/Generator.c
@@ -157,6 +157,13 @@ static void ImprovedNoise_Init(cc_uint8* p, RNGState* rnd) {
 	}
 }
 
+/* Normally, calculating Grad involves a function call + switch. However, the table combinations
+  can be directly packed into a set of bit flags (where each 2 bit combination indicates either -1, 0 1).
+  This avoids needing to call another function that performs branching */
+#define X_FLAGS 0x46552222
+#define Y_FLAGS 0x2222550A
+#define Grad(hash, x, y) (((X_FLAGS >> (hash)) & 3) - 1) * (x) + (((Y_FLAGS >> (hash)) & 3) - 1) * (y);
+
 static float ImprovedNoise_Calc(const cc_uint8* p, float x, float y) {
 	int xFloor, yFloor, X, Y;
 	float u, v;
@@ -173,22 +180,16 @@ static float ImprovedNoise_Calc(const cc_uint8* p, float x, float y) {
 	v = y * y * y * (y * (y * 6 - 15) + 10); /* Fade(y) */
 	A = p[X] + Y; B = p[X + 1] + Y;
 
-	/* Normally, calculating Grad involves a function call. However, we can directly pack this table
-	(since each value indicates either -1, 0 1) into a set of bit flags. This way we avoid needing
-	to call another function that performs branching */
-#define xFlags 0x46552222
-#define yFlags 0x2222550A
-
 	hash = (p[p[A]] & 0xF) << 1;
-	g22  = (((xFlags >> hash) & 3) - 1) * x       + (((yFlags >> hash) & 3) - 1) * y; /* Grad(p[p[A], x, y) */
+	g22  = Grad(hash, x,     y); /* Grad(p[p[A], x,     y) */
 	hash = (p[p[B]] & 0xF) << 1;
-	g12  = (((xFlags >> hash) & 3) - 1) * (x - 1) + (((yFlags >> hash) & 3) - 1) * y; /* Grad(p[p[B], x - 1, y) */
+	g12  = Grad(hash, x - 1, y); /* Grad(p[p[B], x - 1, y) */
 	c1   = g22 + u * (g12 - g22);
 
 	hash = (p[p[A + 1]] & 0xF) << 1;
-	g21  = (((xFlags >> hash) & 3) - 1) * x       + (((yFlags >> hash) & 3) - 1) * (y - 1); /* Grad(p[p[A + 1], x, y - 1) */
+	g21  = Grad(hash, x,     y - 1); /* Grad(p[p[A + 1], x,     y - 1) */
 	hash = (p[p[B + 1]] & 0xF) << 1;
-	g11  = (((xFlags >> hash) & 3) - 1) * (x - 1) + (((yFlags >> hash) & 3) - 1) * (y - 1); /* Grad(p[p[B + 1], x - 1, y - 1) */
+	g11  = Grad(hash, x - 1, y - 1); /* Grad(p[p[B + 1], x - 1, y - 1) */
 	c2   = g21 + u * (g11 - g21);
 
 	return c1 + v * (c2 - c1);
diff --git a/src/Screens.c b/src/Screens.c
index ff022e506..e27de0a64 100644
--- a/src/Screens.c
+++ b/src/Screens.c
@@ -1005,6 +1005,7 @@ static int ChatScreen_ClampChatIndex(int index) {
 static void ChatScreen_ScrollChatBy(struct ChatScreen* s, int delta) {
 	int newIndex = ChatScreen_ClampChatIndex(s->chatIndex + delta);
 	delta = newIndex - s->chatIndex;
+	if (Game_PureClassic) return;
 
 	while (delta) {
 		if (delta < 0) {