From 5d88fa9cf50880e1923d93c4621167e0d83b3858 Mon Sep 17 00:00:00 2001
From: Nikita Edel <nikitagussew@gmail.com>
Date: Wed, 11 Mar 2026 20:02:11 +0100
Subject: [PATCH] add explanation

---
 Minecraft.World/Util/Mth.cpp | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/Minecraft.World/Util/Mth.cpp b/Minecraft.World/Util/Mth.cpp
index 54f7fb605..b290b5877 100644
--- a/Minecraft.World/Util/Mth.cpp
+++ b/Minecraft.World/Util/Mth.cpp
@@ -10,13 +10,16 @@ const float Mth::RADDEG = 180.0f / PI;
 
 float *Mth::_sin = NULL;
 
+// 4jcraft for clarity
+constexpr size_t SIN_TAB_CNT = 65536;
+
 const float Mth::sinScale = 65536.0f / (float) (PI * 2);
 
 // 4J - added - was in static constructor
 void Mth::init()
 {
-    _sin = new float[65536];
-    for (int i = 0; i < 65536; i++)
+    _sin = new float[SIN_TAB_CNT];
+    for (int i = 0; i < SIN_TAB_CNT; i++)
 	{
         _sin[i] = (float) ::sin(i * PI * 2 / 65536.0f);
     }
@@ -24,16 +27,27 @@ void Mth::init()
 
 float Mth::sin(float i)
 {
+	
 	if(_sin == NULL) init();		// 4J - added
-	return _sin[(int)fmodf(i * sinScale, 65536.0f) & 65535];
+
+	// 4jcraft changed, what ever this was, it was not safe
+	// fmodf returns between -65536 and 65536 (casted)
+	// last end is there to shift it into 0 to 65535
+	
+	return _sin[(int32_t) fmodf(i * sinScale, (float) SIN_TAB_CNT) & (SIN_TAB_CNT - 1)];
 }
 
 float Mth::cos(float i)
 {
 	if(_sin == NULL) init();		// 4J - added
-	return _sin[(int)fmodf(i * sinScale + 16384.0f, 65536.0f) & 65535];
+	// 4jcraft same thing as ::sin but shift by SIN_TAB_CNT / 4 
+	// which is aquivalent to shift by pi / 2
+	// and again the same modulo logic to cramp and map it onto the computed table
+	
+	return _sin[(int32_t) fmodf(i * sinScale + ((float) SIN_TAB_CNT / 4), (float)SIN_TAB_CNT) & (SIN_TAB_CNT - 1)];
 }
 
+
 float Mth::sqrt(float x)
 {
 	return (float) ::sqrt(x);