Check for FMA

common/src/main/java/net/irisshaders/iris/shadows/frustum/advanced/AdvancedShadowCullingFrustum.java

@@ -1,5 +1,7 @@
 package net.irisshaders.iris.shadows.frustum.advanced;
 
+import com.sun.management.HotSpotDiagnosticMXBean;
+import com.sun.management.VMOption;
 import net.caffeinemc.mods.sodium.client.render.viewport.Viewport;
 import net.caffeinemc.mods.sodium.client.render.viewport.ViewportProvider;
 import net.irisshaders.iris.shadows.frustum.BoxCuller;
@@ -10,6 +12,8 @@
 import org.joml.Vector3f;
 import org.joml.Vector4f;
 
+import java.lang.management.ManagementFactory;
+
 /**
  * A Frustum implementation that derives a tightly-fitted shadow pass frustum based on the player's camera frustum and
  * an assumption that the shadow map will only be sampled for the purposes of direct shadow casting, volumetric lighting,
@@ -312,6 +316,25 @@ protected int isVisible(double minX, double minY, double minZ, double maxX, doub
 		return this.checkCornerVisibility(f, g, h, i, j, k);
 	}
 
+	private static final boolean FMA_SUPPORT;
+
+	static {
+		// Automatically enable `joml.useMathFma` system property if JVM UseFMA is enabled.
+		// The JVM will automatically enable the UseFMA vm option if the cpu supports it.
+		// Thanks to kunzite for making me aware of this.
+		final HotSpotDiagnosticMXBean hotSpotDiagnostic = ManagementFactory.getPlatformMXBean(HotSpotDiagnosticMXBean.class);
+		if (hotSpotDiagnostic == null) {
+			FMA_SUPPORT = false;
+		} else {
+			final VMOption useFMAVMOption = hotSpotDiagnostic.getVMOption("UseFMA");
+			FMA_SUPPORT = Boolean.parseBoolean(useFMAVMOption.getValue());
+		}
+	}
+
+	private static float safeFMA(float a, float b, float c) {
+		return a * b + c;
+	}
+
 	/**
 	 * Checks corner visibility.
 	 *
@@ -330,13 +353,19 @@ protected int checkCornerVisibility(float minX, float minY, float minZ, float ma
 			// Check if plane is inside or intersecting.
 			// This is ported from JOML's FrustumIntersection.
 
-			float outsideBoundX = (plane.x() < 0) ? minX : maxX;
-			float outsideBoundY = (plane.y() < 0) ? minY : maxY;
-			float outsideBoundZ = (plane.z() < 0) ? minZ : maxZ;
+			float outsideBoundX = (plane.x < 0) ? minX : maxX;
+			float outsideBoundY = (plane.y < 0) ? minY : maxY;
+			float outsideBoundZ = (plane.z < 0) ? minZ : maxZ;
 
 			// Use Math.fma for the dot product calculation to get vectorization (sorry old Intel users)
-			if (Math.fma(plane.x(), outsideBoundX, Math.fma(plane.y(), outsideBoundY, plane.z() * outsideBoundZ)) < -plane.w()) {
-				return 0;
+			if (FMA_SUPPORT) {
+				if (Math.fma(plane.x, outsideBoundX, Math.fma(plane.y, outsideBoundY, plane.z * outsideBoundZ)) < -plane.w) {
+					return 0;
+				}
+			} else {
+				if (safeFMA(plane.x, outsideBoundX, safeFMA(plane.y, outsideBoundY, plane.z * outsideBoundZ)) < -plane.w) {
+					return 0;
+				}
 			}
 		}