Yatopia/patches/server/0062-Lithium-CompactSineLUT.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: JellySquid <jellysquid+atwork@protonmail.com>
Date: Fri, 5 Feb 2021 00:16:30 -0600
Subject: [PATCH] Lithium: CompactSineLUT

Original code by JellySquid, licensed under GNU Lesser General Public License v3.0
you can find the original code on https://github.com/CaffeineMC/lithium-fabric/ (Yarn mappings)

diff --git a/src/main/java/net/minecraft/util/MathHelper.java b/src/main/java/net/minecraft/util/MathHelper.java
index e9e7fcf2b63febe2a7d055826fabb86bc13a5cf3..b95115aca72ba0cf6451096ddbd8b50a8f3bb5c6 100644
--- a/src/main/java/net/minecraft/util/MathHelper.java
+++ b/src/main/java/net/minecraft/util/MathHelper.java
@@ -5,6 +5,7 @@ import java.util.UUID;
 import java.util.function.IntPredicate;
 import net.minecraft.SystemUtils;
 import net.minecraft.core.BaseBlockPosition;
+import org.yatopiamc.yatopia.server.math.CompactSineLUT;
 
 public class MathHelper {
 
@@ -15,6 +16,7 @@ public class MathHelper {
         }
 
     });
+    public static float[] getSinTable() { return b; } // Yatopia - OBFHELPER
     private static final Random c = new Random();
     private static final int[] d = new int[]{0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9};
     private static final double e = Double.longBitsToDouble(4805340802404319232L);
@@ -22,11 +24,11 @@ public class MathHelper {
     private static final double[] g = new double[257];
 
     public static float sin(float f) {
-        return MathHelper.b[(int) (f * 10430.378F) & '\uffff'];
+        return CompactSineLUT.sin(f); // Yatopia - CompactSineLUT
     }
 
     public static float cos(float f) {
-        return MathHelper.b[(int) (f * 10430.378F + 16384.0F) & '\uffff'];
+        return CompactSineLUT.cos(f); // Yatopia - CompactSineLUT
     }
 
     public static float c(float f) {
diff --git a/src/main/java/org/yatopiamc/yatopia/server/math/CompactSineLUT.java b/src/main/java/org/yatopiamc/yatopia/server/math/CompactSineLUT.java
new file mode 100644
index 0000000000000000000000000000000000000000..1bb8ba3836af872bc2e58898f16a0b91036b9b02
--- /dev/null
+++ b/src/main/java/org/yatopiamc/yatopia/server/math/CompactSineLUT.java
@@ -0,0 +1,90 @@
+package org.yatopiamc.yatopia.server.math;
+
+import net.minecraft.util.MathHelper;
+
+/**
+ * A replacement for the sine angle lookup table used in {@link MathHelper}, both reducing the size of LUT and improving
+ * the access patterns for common paired sin/cos operations.
+ *
+ *  sin(-x) = -sin(x)
+ *    ... to eliminate negative angles from the LUT.
+ *
+ *  sin(x) = sin(pi/2 - x)
+ *    ... to eliminate supplementary angles from the LUT.
+ *
+ * Using these identities allows us to reduce the LUT from 64K entries (256 KB) to just 16K entries (64 KB), enabling
+ * it to better fit into the CPU's caches at the expense of some cycles on the fast path. The implementation has been
+ * tightly optimized to avoid branching where possible and to use very quick integer operations.
+ *
+ * Generally speaking, reducing the size of a lookup table is always a good optimization, but since we need to spend
+ * extra CPU cycles trying to maintain parity with vanilla, there is the potential risk that this implementation ends
+ * up being slower than vanilla when the lookup table is able to be kept in cache memory.
+ *
+ * Unlike other "fast math" implementations, the values returned by this class are *bit-for-bit identical* with those
+ * from {@link MathHelper}. Validation is performed during runtime to ensure that the table is correct.
+ *
+ * @author coderbot16   Author of the original (and very clever) implementation in Rust:
+ *  https://gitlab.com/coderbot16/i73/-/tree/master/i73-trig/src
+ * @author jellysquid3  Additional optimizations, port to Java
+ */
+public class CompactSineLUT {
+    private static final int[] SINE_TABLE_INT = new int[16384 + 1];
+    private static final float SINE_TABLE_MIDPOINT;
+
+    static {
+        final float[] SINE_TABLE = MathHelper.getSinTable();
+        // Copy the sine table, covering to raw int bits
+        for (int i = 0; i < SINE_TABLE_INT.length; i++) {
+            SINE_TABLE_INT[i] = Float.floatToRawIntBits(SINE_TABLE[i]);
+        }
+
+        SINE_TABLE_MIDPOINT = SINE_TABLE[SINE_TABLE.length / 2];
+
+        // Test that the lookup table is correct during runtime
+        for (int i = 0; i < SINE_TABLE.length; i++) {
+            float expected = SINE_TABLE[i];
+            float value = lookup(i);
+
+            if (expected != value) {
+                throw new IllegalArgumentException(String.format("LUT error at index %d (expected: %s, found: %s)", i, expected, value));
+            }
+        }
+    }
+
+    // [VanillaCopy] MathHelper#sin(float)
+    public static float sin(float f) {
+        return lookup((int) (f * 10430.38) & 0xFFFF);
+    }
+
+    // [VanillaCopy] MathHelper#cos(float)
+    public static float cos(float f) {
+        return lookup((int) (f * 10430.38 + 16384.0) & 0xFFFF);
+    }
+
+    private static float lookup(int index) {
+        // A special case... Is there some way to eliminate this?
+        if (index == 32768) {
+            return SINE_TABLE_MIDPOINT;
+        }
+
+        // Trigonometric identity: sin(-x) = -sin(x)
+        // Given a domain of 0 <= x <= 2*pi, just negate the value if x > pi.
+        // This allows the sin table size to be halved.
+        int neg = (index & 0x8000) << 16;
+
+        // All bits set if (pi/2 <= x), none set otherwise
+        // Extracts the 15th bit from 'half'
+        int mask = (index << 17) >> 31;
+
+        // Trigonometric identity: sin(x) = sin(pi/2 - x)
+        int pos = (0x8001 & mask) + (index ^ mask);
+
+        // Wrap the position in the table. Moving this down to immediately before the array access
+        // seems to help the Hotspot compiler optimize the bit math better.
+        pos &= 0x7fff;
+
+        // Fetch the corresponding value from the LUT and invert the sign bit as needed
+        // This directly manipulate the sign bit on the float bits to simplify logic
+        return Float.intBitsToFloat(SINE_TABLE_INT[pos] ^ neg);
+    }
+}