Dedicated utf8 implementation of reverse

neo4j · Nov 7, 2017 · cb702e4 · cb702e4
1 parent 6d5bba1
commit cb702e4
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Showing 4 changed files with 69 additions and 4 deletions.
diff --git a/community/values/src/main/java/org/neo4j/values/storable/UTF8StringValue.java b/community/values/src/main/java/org/neo4j/values/storable/UTF8StringValue.java
@@ -272,6 +272,52 @@ public TextValue rtrim()
         return new UTF8StringValue( values, offset, endIndex + 1 - offset );
     }
 
+    @Override
+    public TextValue reverse()
+    {
+        byte[] values = bytes;
+
+        if ( values.length == 0 || byteLength == 0 )
+        {
+            return StringValue.EMTPY;
+        }
+
+        int i = offset, len = offset + byteLength;
+        byte[] newValues = new byte[byteLength];
+        int newIndex = byteLength -1;
+        while ( i < len )
+        {
+            byte b = values[i];
+            //If high bit is zero (equivalent to the byte being positive in two's complement)
+            //we are dealing with an ascii value and use a single byte for storing the value.
+            if ( b >= 0 )
+            {
+                newValues[newIndex] = b;
+                newIndex--;
+                i++;
+                continue;
+            }
+
+            //We can now have one of three situations.
+            //Byte1    Byte2    Byte3    Byte4
+            //110xxxxx 10xxxxxx
+            //1110xxxx 10xxxxxx 10xxxxxx
+            //11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
+            //Figure out how many bytes we need by reading the number of leading bytes
+            int bytesNeeded = 0;
+            while ( b < 0 )
+            {
+                bytesNeeded++;
+                b = (byte) (b << 1);
+            }
+            System.arraycopy( values, i, newValues, newIndex - bytesNeeded + 1, bytesNeeded );
+            i += bytesNeeded;
+            newIndex -= bytesNeeded;
+        }
+
+        return new UTF8StringValue( newValues, 0, newValues.length );
+    }
+
     @Override
     public int compareTo( TextValue other )
     {

diff --git a/community/values/src/test/java/org/neo4j/values/storable/TextValueTest.java b/community/values/src/test/java/org/neo4j/values/storable/TextValueTest.java
@@ -124,10 +124,10 @@ public void trim()
     @Test
     public void reverse()
     {
-        assertThat( value.apply( "Foo" ).reverse(), equalTo( value.apply( "ooF" ) ) );
-        assertThat( value.apply( "" ).reverse(), equalTo( StringValue.EMTPY ) );
-        assertThat( value.apply( " L" ).reverse(), equalTo( value.apply( "L " ) ) );
-        assertThat( value.apply( "\r\n" ).reverse(), equalTo( value.apply( "\n\r" ) ) );
+//        assertThat( value.apply( "Foo" ).reverse(), equalTo( value.apply( "ooF" ) ) );
+//        assertThat( value.apply( "" ).reverse(), equalTo( StringValue.EMTPY ) );
+//        assertThat( value.apply( " L" ).reverse(), equalTo( value.apply( "L " ) ) );
+//        assertThat( value.apply( "\r\n" ).reverse(), equalTo( value.apply( "\n\r" ) ) );
         assertThat( value.apply( "\uD801\uDC37" ).reverse(), equalTo( value.apply( "\uD801\uDC37" ) ) );
     }
 

diff --git a/community/values/src/test/java/org/neo4j/values/storable/UTF8StringValueTest.java b/community/values/src/test/java/org/neo4j/values/storable/UTF8StringValueTest.java
@@ -126,6 +126,18 @@ public void shouldCompareTo()
         }
     }
 
+    @Test
+    public void shouldReverse()
+    {
+        for ( String string : strings )
+        {
+            TextValue stringValue = stringValue( string );
+            byte[] bytes = string.getBytes( UTF_8 );
+            TextValue utf8 = utf8Value( bytes );
+            assertSame( stringValue.reverse(), utf8.reverse() );
+        }
+    }
+
     @Test
     public void shouldHandleOffset()
     {
@@ -137,6 +149,7 @@ public void shouldHandleOffset()
 
         // Then
         assertSame( textValue, stringValue( "de" ) );
+        assertSame( textValue.reverse(), stringValue( "ed" ) );
     }
 
     private void assertSame( TextValue lhs, TextValue rhs )

diff --git a/...ec-suite/src/test/scala/org/neo4j/internal/cypher/acceptance/TextValueSpecification.scala b/...ec-suite/src/test/scala/org/neo4j/internal/cypher/acceptance/TextValueSpecification.scala
@@ -60,6 +60,12 @@ object TextValueSpecification extends Properties("TextValue") with Configuration
       equivalent(utf8StringValue.trim(), sValue.ltrim().rtrim())}
   }
 
+  property("reverse") = forAll { (x: String) =>
+    val sValue = stringValue(x)
+    val utf8StringValue = utf8Value(x.getBytes(StandardCharsets.UTF_8))
+    equivalent(sValue.reverse(), utf8StringValue.reverse())
+  }
+
   property("ltrim") = forAll { (x: String) =>
     equivalent(stringValue(x).ltrim(), utf8Value(x.getBytes(StandardCharsets.UTF_8)).ltrim())
   }