Optimize GTUtility.getTier call (#3165)

Co-authored-by: kstvr32 <kstvr32@gmail.com>
Co-authored-by: Martin Robertz <dream-master@gmx.net>

2 files changed, 33 insertions, 3 deletions

diff --git a/src/main/java/gregtech/api/util/GTUtility.java b/src/main/java/gregtech/api/util/GTUtility.java
index 8eeb71753e..ede680ba62 100644
--- a/src/main/java/gregtech/api/util/GTUtility.java
+++ b/src/main/java/gregtech/api/util/GTUtility.java
@@ -500,9 +500,15 @@ public class GTUtility {
     }
 
     public static byte getTier(long l) {
-        byte i = -1;
-        while (++i < V.length) if (l <= V[i]) return i;
-        return (byte) (V.length - 1);
+        if (l > V[14]) return 15;
+        if (l <= V[0]) return 0;
+
+        // numberOfLeadingZeros is implemented in hardware by x86 LZCNT
+        // and is extremely efficient (takes only a couple of hardware cycles)
+        // (64 - numberOfLeadingZeros(l - 1)) = ceil(log_2(l))
+        int log2L = 64 - Long.numberOfLeadingZeros(l - 1);
+
+        return (byte) ((log2L - 2) / 2);
     }
 
     public static long getAmperageForTier(long voltage, byte tier) {
diff --git a/src/test/java/gregtech/api/util/GTUtilityTest.java b/src/test/java/gregtech/api/util/GTUtilityTest.java
new file mode 100644
index 0000000000..bb6632cd41
--- /dev/null
+++ b/src/test/java/gregtech/api/util/GTUtilityTest.java
@@ -0,0 +1,24 @@
+package gregtech.api.util;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+import gregtech.api.enums.GTValues;
+
+public class GTUtilityTest {
+
+    @Test
+    public void testGetTier() {
+        assertEquals(0, GTUtility.getTier(-1));
+        assertEquals(0, GTUtility.getTier(1));
+        assertEquals(0, GTUtility.getTier(GTValues.V[0]));
+        for (int i = 1; i < 16; i++) {
+            assertEquals(
+                i,
+                GTUtility.getTier(GTValues.V[i - 1] + 1),
+                String.format("%d, %d", i, GTValues.V[i - 1] + 1));
+            assertEquals(i, GTUtility.getTier(GTValues.V[i]));
+        }
+    }
+}