Add IntegerCompressor.compressionMode

2 files changed, 21 insertions, 0 deletions

diff --git a/vespajlib/src/main/java/com/yahoo/compress/IntegerCompressor.java b/vespajlib/src/main/java/com/yahoo/compress/IntegerCompressor.java
index fada7243b95..42178fa3ffd 100644
--- a/vespajlib/src/main/java/com/yahoo/compress/IntegerCompressor.java
+++ b/vespajlib/src/main/java/com/yahoo/compress/IntegerCompressor.java
@@ -10,6 +10,14 @@ import java.nio.ByteBuffer;
  */
 public class IntegerCompressor {
 
+    public enum Mode { NONE, COMPRESSED, COMPRESSED_POSITIVE; }
+
+    public static Mode compressionMode(int min, int max) {
+        if (min >= 0 && max < 1 << 30) return Mode.COMPRESSED_POSITIVE;
+        if (min > -1 << 29 && max < 1 << 29) return Mode.COMPRESSED;
+        return Mode.NONE;
+    }
+
     public static void putCompressedNumber(int n, ByteBuffer buf) {
         int negative = n < 0 ? 0x80 : 0x0;
         if (negative != 0) {
diff --git a/vespajlib/src/test/java/com/yahoo/compress/IntegerCompressorTest.java b/vespajlib/src/test/java/com/yahoo/compress/IntegerCompressorTest.java
index 921ae6746be..c53a834659c 100644
--- a/vespajlib/src/test/java/com/yahoo/compress/IntegerCompressorTest.java
+++ b/vespajlib/src/test/java/com/yahoo/compress/IntegerCompressorTest.java
@@ -1,6 +1,7 @@
 // Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.compress;
 
+import com.yahoo.compress.IntegerCompressor.Mode;
 import org.junit.Test;
 
 import java.nio.ByteBuffer;
@@ -91,6 +92,18 @@ public class IntegerCompressorTest {
                      assertThrows(IllegalArgumentException.class, () -> verifyNumber(-0x80000000, mx80000000)).getMessage());
     }
 
+    @Test
+    public void testMode() {
+        assertEquals(Mode.NONE,                IntegerCompressor.compressionMode(-0x80000000,  0x00000000));
+        assertEquals(Mode.NONE,                IntegerCompressor.compressionMode(-0x20000000,  0x00000000));
+        assertEquals(Mode.NONE,                IntegerCompressor.compressionMode(-0x00000001,  0x3fffffff));
+        assertEquals(Mode.COMPRESSED,          IntegerCompressor.compressionMode(-0x1fffffff,  0x1fffffff));
+        assertEquals(Mode.COMPRESSED,          IntegerCompressor.compressionMode(-0x1fffffff, -0x1fffffff));
+        assertEquals(Mode.COMPRESSED,          IntegerCompressor.compressionMode(-0x1fffffff,  0x00000000));
+        assertEquals(Mode.COMPRESSED,          IntegerCompressor.compressionMode(-0x00000001,  0x1fffffff));
+        assertEquals(Mode.COMPRESSED_POSITIVE, IntegerCompressor.compressionMode( 0x00000000,  0x00000000));
+        assertEquals(Mode.COMPRESSED_POSITIVE, IntegerCompressor.compressionMode( 0x00000000,  0x3fffffff));
+        assertEquals(Mode.COMPRESSED_POSITIVE, IntegerCompressor.compressionMode( 0x3fffffff,  0x3fffffff));
     }
 
 }