145 lines
6.4 KiB
Diff
145 lines
6.4 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: "Sofiane H. Djerbi" <46628754+kugge@users.noreply.github.com>
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Date: Fri, 17 Feb 2023 00:34:31 +0200
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Subject: [PATCH] Lithium Math SineLut
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Author: JellySquid
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Licence: LGPL-3.0
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diff --git a/src/main/java/dev/kaiijumc/kaiiju/KaiijuConfig.java b/src/main/java/dev/kaiijumc/kaiiju/KaiijuConfig.java
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index 9020f9d2ce1a0612f21fb0ba25c07c752475bb5a..dca9c796317b988ae5963dd2d452c2b8162a2249 100644
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--- a/src/main/java/dev/kaiijumc/kaiiju/KaiijuConfig.java
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+++ b/src/main/java/dev/kaiijumc/kaiiju/KaiijuConfig.java
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@@ -219,8 +219,10 @@ public class KaiijuConfig {
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public static boolean lithiumEnable = true;
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public static boolean lithiumMathFastUtil = true;
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+ public static boolean lithiumMathSineLut = true;
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private static void lithiumSettings() {
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lithiumEnable = getBoolean("lithium.enable", lithiumEnable);
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lithiumMathFastUtil = getBoolean("lithium.math.fast-util", lithiumMathFastUtil) && lithiumEnable;
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+ lithiumMathSineLut = getBoolean("lithium.math.sine-lut", lithiumMathSineLut) && lithiumEnable;
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}
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}
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diff --git a/src/main/java/me/jellysquid/mods/lithium/common/util/math/CompactSineLUT.java b/src/main/java/me/jellysquid/mods/lithium/common/util/math/CompactSineLUT.java
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new file mode 100644
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index 0000000000000000000000000000000000000000..ccb45e94ea6d1a627df786fb88baec7edd1f2427
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--- /dev/null
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+++ b/src/main/java/me/jellysquid/mods/lithium/common/util/math/CompactSineLUT.java
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@@ -0,0 +1,90 @@
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+package me.jellysquid.mods.lithium.common.util.math;
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+
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+import net.minecraft.util.Mth;
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+
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+/**
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+ * A replacement for the sine angle lookup table used in {@link MathHelper}, both reducing the size of LUT and improving
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+ * the access patterns for common paired sin/cos operations.
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+ *
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+ * sin(-x) = -sin(x)
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+ * ... to eliminate negative angles from the LUT.
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+ *
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+ * sin(x) = sin(pi/2 - x)
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+ * ... to eliminate supplementary angles from the LUT.
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+ *
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+ * Using these identities allows us to reduce the LUT from 64K entries (256 KB) to just 16K entries (64 KB), enabling
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+ * it to better fit into the CPU's caches at the expense of some cycles on the fast path. The implementation has been
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+ * tightly optimized to avoid branching where possible and to use very quick integer operations.
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+ *
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+ * Generally speaking, reducing the size of a lookup table is always a good optimization, but since we need to spend
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+ * extra CPU cycles trying to maintain parity with vanilla, there is the potential risk that this implementation ends
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+ * up being slower than vanilla when the lookup table is able to be kept in cache memory.
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+ *
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+ * Unlike other "fast math" implementations, the values returned by this class are *bit-for-bit identical* with those
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+ * from {@link MathHelper}. Validation is performed during runtime to ensure that the table is correct.
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+ *
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+ * @author coderbot16 Author of the original (and very clever) implementation in Rust:
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+ * https://gitlab.com/coderbot16/i73/-/tree/master/i73-trig/src
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+ * @author jellysquid3 Additional optimizations, port to Java
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+ */
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+public class CompactSineLUT {
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+ private static final int[] SINE_TABLE_INT = new int[16384 + 1];
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+ private static final float SINE_TABLE_MIDPOINT;
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+
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+ static {
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+ final float[] SINE_TABLE = Mth.getSinTable();
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+ // Copy the sine table, covering to raw int bits
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+ for (int i = 0; i < SINE_TABLE_INT.length; i++) {
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+ SINE_TABLE_INT[i] = Float.floatToRawIntBits(SINE_TABLE[i]);
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+ }
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+
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+ SINE_TABLE_MIDPOINT = SINE_TABLE[SINE_TABLE.length / 2];
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+
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+ // Test that the lookup table is correct during runtime
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+ for (int i = 0; i < SINE_TABLE.length; i++) {
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+ float expected = SINE_TABLE[i];
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+ float value = lookup(i);
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+
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+ if (expected != value) {
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+ throw new IllegalArgumentException(String.format("LUT error at index %d (expected: %s, found: %s)", i, expected, value));
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+ }
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+ }
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+ }
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+
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+ // [VanillaCopy] MathHelper#sin(float)
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+ public static float sin(float f) {
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+ return lookup((int) (f * 10430.378f) & 0xFFFF);
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+ }
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+
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+ // [VanillaCopy] MathHelper#cos(float)
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+ public static float cos(float f) {
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+ return lookup((int) (f * 10430.378f + 16384.0f) & 0xFFFF);
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+ }
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+
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+ private static float lookup(int index) {
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+ // A special case... Is there some way to eliminate this?
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+ if (index == 32768) {
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+ return SINE_TABLE_MIDPOINT;
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+ }
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+
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+ // Trigonometric identity: sin(-x) = -sin(x)
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+ // Given a domain of 0 <= x <= 2*pi, just negate the value if x > pi.
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+ // This allows the sin table size to be halved.
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+ int neg = (index & 0x8000) << 16;
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+
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+ // All bits set if (pi/2 <= x), none set otherwise
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+ // Extracts the 15th bit from 'half'
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+ int mask = (index << 17) >> 31;
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+
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+ // Trigonometric identity: sin(x) = sin(pi/2 - x)
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+ int pos = (0x8001 & mask) + (index ^ mask);
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+
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+ // Wrap the position in the table. Moving this down to immediately before the array access
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+ // seems to help the Hotspot compiler optimize the bit math better.
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+ pos &= 0x7fff;
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+
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+ // Fetch the corresponding value from the LUT and invert the sign bit as needed
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+ // This directly manipulate the sign bit on the float bits to simplify logic
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+ return Float.intBitsToFloat(SINE_TABLE_INT[pos] ^ neg);
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+ }
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+}
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\ No newline at end of file
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diff --git a/src/main/java/net/minecraft/util/Mth.java b/src/main/java/net/minecraft/util/Mth.java
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index 618f19d70a61062ed5989ec6cf0c036f2e047466..dd320f3a3f2b51a723a2fcc65d477a22c0901455 100644
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--- a/src/main/java/net/minecraft/util/Mth.java
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+++ b/src/main/java/net/minecraft/util/Mth.java
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@@ -45,11 +45,19 @@ public class Mth {
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return (float)((int)(value * f)) / f;
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}
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+ // Kaiiju start
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+ public static float[] getSinTable() {
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+ return SIN;
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+ }
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+ // Kaiiju end
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+
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public static float sin(float value) {
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+ if (dev.kaiijumc.kaiiju.KaiijuConfig.lithiumMathSineLut) return me.jellysquid.mods.lithium.common.util.math.CompactSineLUT.sin(value); // Kaiiju
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return SIN[(int)(value * 10430.378F) & '\uffff'];
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}
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public static float cos(float value) {
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+ if (dev.kaiijumc.kaiiju.KaiijuConfig.lithiumMathSineLut) return me.jellysquid.mods.lithium.common.util.math.CompactSineLUT.cos(value); // Kaiiju
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return SIN[(int)(value * 10430.378F + 16384.0F) & '\uffff'];
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}
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