From 9bc391d09b6043ce6f3dc2eb1c5207a309c56775 Mon Sep 17 00:00:00 2001
From: hneemann <helmut.neemann@arcor.de>
Date: Tue, 4 Jul 2017 22:50:12 +0200
Subject: [PATCH] added a getValueSigned() function to ObservableValue

---
 .../neemann/digital/core/ObservableValue.java | 13 ++++++++++++
 .../digital/core/ObservableValueTest.java     | 20 +++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/src/main/java/de/neemann/digital/core/ObservableValue.java b/src/main/java/de/neemann/digital/core/ObservableValue.java
index 943f729fe..7cccf8d9a 100644
--- a/src/main/java/de/neemann/digital/core/ObservableValue.java
+++ b/src/main/java/de/neemann/digital/core/ObservableValue.java
@@ -11,6 +11,7 @@ public class ObservableValue extends Observable implements PinDescription {
 
     private final String name;
     private final long mask;
+    private final long signedFlag;
     private final boolean supportsHighZ;
     private final int bits;
     private long value;
@@ -45,6 +46,7 @@ public class ObservableValue extends Observable implements PinDescription {
             mask = -1;
         else
             mask = (1L << bits) - 1;
+        signedFlag = 1 << (bits - 1);
         this.name = name;
         supportsHighZ = highZ;
     }
@@ -140,6 +142,17 @@ public class ObservableValue extends Observable implements PinDescription {
         }
     }
 
+    /**
+     * returns the actual value as a signed long
+     *
+     * @return the signed value
+     */
+    public long getValueSigned() {
+        long v = getValue();
+        if ((v & signedFlag) != 0) v |= ~mask;
+        return v;
+    }
+
     /**
      * converts a value to a minimal hex string
      *
diff --git a/src/test/java/de/neemann/digital/core/ObservableValueTest.java b/src/test/java/de/neemann/digital/core/ObservableValueTest.java
index 4c546dc1a..abca4784e 100644
--- a/src/test/java/de/neemann/digital/core/ObservableValueTest.java
+++ b/src/test/java/de/neemann/digital/core/ObservableValueTest.java
@@ -25,4 +25,24 @@ public class ObservableValueTest extends TestCase {
         assertEquals((1L << 62) - 1, v.getValue());
     }
 
+    public void testSigned() {
+        ObservableValue v = new ObservableValue("z", 4);
+        assertEquals(0, v.setValue(0).getValueSigned());
+        assertEquals(1, v.setValue(1).getValueSigned());
+        assertEquals(7, v.setValue(7).getValueSigned());
+        assertEquals(-8, v.setValue(8).getValueSigned());
+        assertEquals(-1, v.setValue(15).getValueSigned());
+        assertEquals(-1, v.setValue(-1).getValueSigned());
+
+        v = new ObservableValue("z", 1);
+        assertEquals(0, v.setValue(0).getValueSigned());
+        assertEquals(-1, v.setValue(1).getValueSigned());
+
+        v = new ObservableValue("z", 8);
+        assertEquals(127, v.setValue(127).getValueSigned());
+        assertEquals(-128, v.setValue(128).getValueSigned());
+        assertEquals(255, v.setValue(-1).getValue());
+        assertEquals(-1, v.setValue(-1).getValueSigned());
+    }
+
 }
\ No newline at end of file