* Upon Pointer.getPointer(Class<P>) scale position, limit, and…

… `capacity` with `sizeof()` (pull #476)
bytedeco · May 12, 2021 · 577239c · 577239c
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,4 +1,5 @@
 
+ * Upon `Pointer.getPointer(Class<P>)` scale `position`, `limit`, and `capacity` with `sizeof()` ([pull #476](https://github.com/bytedeco/javacpp/pull/476))
  * Fix `Parser` incorrectly translating non-documentation comments as part of documentation comments ([issue #475](https://github.com/bytedeco/javacpp/issues/475))
  * Set `Pointer.maxPhysicalBytes` to `4 * Runtime.maxMemory()` by default as workaround for memory-mapped files, ZGC, etc ([issue #468](https://github.com/bytedeco/javacpp/issues/468))
  * Ensure `synchronized` code in `Pointer` gets skipped with "org.bytedeco.javacpp.nopointergc" ([issue tensorflow/java#313](https://github.com/tensorflow/java/issues/313))

diff --git a/src/main/java/org/bytedeco/javacpp/Pointer.java b/src/main/java/org/bytedeco/javacpp/Pointer.java
@@ -895,15 +895,20 @@ public <P extends Pointer> P getPointer(long i) {
         return (P)getPointer(getClass(), i);
     }
 
-    /** Returns {@code getPointer(cls, 0)}. */
-    public <P extends Pointer> P getPointer(Class<P> cls) {
-        return getPointer(cls, 0);
+    /** Returns {@code getPointer(type, 0)}. */
+    public <P extends Pointer> P getPointer(Class<P> type) {
+        return getPointer(type, 0);
     }
 
-    /** Returns {@code new P(this).offsetAddress(i)}. Throws RuntimeException if constructor is missing. */
-    public <P extends Pointer> P getPointer(Class<P> cls, long i) {
+    /** Returns {@code new P(this).offsetAddress(i)} after scaling {@link #position}, {@link #limit}, and {@link #capacity}
+     *  with {@link #sizeof()}. Throws RuntimeException if the cast constructor is missing from the subclass type. */
+    public <P extends Pointer> P getPointer(Class<P> type, long i) {
         try {
-            return cls.getDeclaredConstructor(Pointer.class).newInstance(this).offsetAddress(i);
+            P p = type.getDeclaredConstructor(Pointer.class).newInstance(this);
+            p.position = position != 0 ? Math.max(0, position * this.sizeof() / p.sizeof()) : 0;
+            p.limit    = limit    != 0 ? Math.max(0, limit    * this.sizeof() / p.sizeof()) : 0;
+            p.capacity = capacity != 0 ? Math.max(0, capacity * this.sizeof() / p.sizeof()) : 0;
+            return p.offsetAddress(i);
         } catch (ReflectiveOperationException e) {
             throw new RuntimeException(e);
         }

diff --git a/src/test/java/org/bytedeco/javacpp/PointerTest.java b/src/test/java/org/bytedeco/javacpp/PointerTest.java
@@ -169,6 +169,10 @@ static class TestFunction extends FunctionPointer {
         assertEquals(pointer.address() + 10, p2.address());
         assertEquals(array.length - 10, p2.limit());
         assertEquals(array.length - 10, p2.capacity());
+        Pointer p3 = pointer.getPointer(Pointer.class, 20);
+        assertEquals(pointer.address() + 20, p3.address());
+        assertEquals(1 * array.length - 20, p3.limit());
+        assertEquals(1 * array.length - 20, p3.capacity());
 
         for (int i = 0; i < array.length; i++) {
             array[i] = (byte)i;
@@ -279,6 +283,10 @@ static class TestFunction extends FunctionPointer {
         assertEquals(pointer.address() + 20, p2.address());
         assertEquals(array.length - 10, p2.limit());
         assertEquals(array.length - 10, p2.capacity());
+        Pointer p3 = pointer.getPointer(Pointer.class, 20);
+        assertEquals(pointer.address() + 20, p3.address());
+        assertEquals(2 * array.length - 20, p3.limit());
+        assertEquals(2 * array.length - 20, p3.capacity());
 
         for (int i = 0; i < array.length; i++) {
             array[i] = (short)i;
@@ -367,6 +375,10 @@ static class TestFunction extends FunctionPointer {
         assertEquals(pointer.address() + 40, p2.address());
         assertEquals(array.length - 10, p2.limit());
         assertEquals(array.length - 10, p2.capacity());
+        Pointer p3 = pointer.getPointer(Pointer.class, 20);
+        assertEquals(pointer.address() + 20, p3.address());
+        assertEquals(4 * array.length - 20, p3.limit());
+        assertEquals(4 * array.length - 20, p3.capacity());
 
         for (int i = 0; i < array.length; i++) {
             array[i] = i;
@@ -455,6 +467,10 @@ static class TestFunction extends FunctionPointer {
         assertEquals(pointer.address() + 80, p2.address());
         assertEquals(array.length - 10, p2.limit());
         assertEquals(array.length - 10, p2.capacity());
+        Pointer p3 = pointer.getPointer(Pointer.class, 20);
+        assertEquals(pointer.address() + 20, p3.address());
+        assertEquals(8 * array.length - 20, p3.limit());
+        assertEquals(8 * array.length - 20, p3.capacity());
 
         for (int i = 0; i < array.length; i++) {
             array[i] = i;
@@ -543,6 +559,10 @@ static class TestFunction extends FunctionPointer {
         assertEquals(pointer.address() + 40, p2.address());
         assertEquals(array.length - 10, p2.limit());
         assertEquals(array.length - 10, p2.capacity());
+        Pointer p3 = pointer.getPointer(Pointer.class, 20);
+        assertEquals(pointer.address() + 20, p3.address());
+        assertEquals(4 * array.length - 20, p3.limit());
+        assertEquals(4 * array.length - 20, p3.capacity());
 
         for (int i = 0; i < array.length; i++) {
             array[i] = i;
@@ -631,6 +651,10 @@ static class TestFunction extends FunctionPointer {
         assertEquals(pointer.address() + 80, p2.address());
         assertEquals(array.length - 10, p2.limit());
         assertEquals(array.length - 10, p2.capacity());
+        Pointer p3 = pointer.getPointer(Pointer.class, 20);
+        assertEquals(pointer.address() + 20, p3.address());
+        assertEquals(8 * array.length - 20, p3.limit());
+        assertEquals(8 * array.length - 20, p3.capacity());
 
         for (int i = 0; i < array.length; i++) {
             array[i] = i;
@@ -719,6 +743,10 @@ static class TestFunction extends FunctionPointer {
         assertEquals(pointer.address() + 20, p2.address());
         assertEquals(array.length - 10, p2.limit());
         assertEquals(array.length - 10, p2.capacity());
+        Pointer p3 = pointer.getPointer(Pointer.class, 20);
+        assertEquals(pointer.address() + 20, p3.address());
+        assertEquals(2 * array.length - 20, p3.limit());
+        assertEquals(2 * array.length - 20, p3.capacity());
 
         for (int i = 0; i < array.length; i++) {
             array[i] = (char)i;
@@ -807,6 +835,10 @@ static class TestFunction extends FunctionPointer {
         assertEquals(pointer.address() + 10, p2.address());
         assertEquals(array.length - 10, p2.limit());
         assertEquals(array.length - 10, p2.capacity());
+        LongPointer p3 = pointer.getPointer(LongPointer.class, 20);
+        assertEquals(pointer.address() + 8 * 20, p3.address());
+        assertEquals(array.length / 8 - 20, p3.limit());
+        assertEquals(array.length / 8 - 20, p3.capacity());
 
         for (int i = 0; i < array.length; i++) {
             array[i] = i % 2 != 0;
@@ -894,6 +926,10 @@ static class TestFunction extends FunctionPointer {
         assertEquals(pointer.address() + 10 * pointerSize, p2.address());
         assertEquals(array.length - 10, p2.limit());
         assertEquals(array.length - 10, p2.capacity());
+        BytePointer p3 = pointer.getPointer(BytePointer.class, 20);
+        assertEquals(pointer.address() + 20, p3.address());
+        assertEquals(pointerSize * array.length - 20, p3.limit());
+        assertEquals(pointerSize * array.length - 20, p3.capacity());
 
         for (int i = 0; i < array.length; i++) {
             final int j = i;