[optimization] Make fn:subsequence lazily evaluated

eXist-db · Sep 2, 2018 · c262649 · c262649
1 parent cc0a5bf
commit c262649
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Showing 2 changed files with 13 additions and 37 deletions.
diff --git a/src/org/exist/xquery/functions/fn/FunSubSequence.java b/src/org/exist/xquery/functions/fn/FunSubSequence.java
@@ -133,43 +133,7 @@ and position() lt fn:round($startingLoc) + fn:round($length)]
                 fromInclusive = startArg;
             }
 
-            // holds the intermittent result
-            Sequence tmp = Sequence.EMPTY_SEQUENCE;
-
-            long position = 1;
-            final SequenceIterator iterator = seq.iterate();
-            if (position != fromInclusive) {
-                // move to start (i.e. fromInclusive)
-                if (iterator.skip(fromInclusive - position) > -1) {
-                    position = fromInclusive;
-                } else {
-                    // SequenceIterator does not support skipping, we have to iterate through each item :-/
-                    for (; position < fromInclusive; position++) {
-                        iterator.nextItem();
-                    }
-                }
-            }
-
-            // copy from start to end
-            while (iterator.hasNext() && position < toExclusive) {
-                final Item item = iterator.nextItem();
-
-                // lazily initialize tmp
-                if (tmp == Sequence.EMPTY_SEQUENCE) {
-                    if (seq instanceof NodeSet) {
-                        tmp = new ExtArrayNodeSet();
-                        ((ExtArrayNodeSet) tmp).keepUnOrdered(unordered);
-                    } else {
-                        tmp = new ValueSequence();
-                        ((ValueSequence) tmp).keepUnOrdered(unordered);
-                    }
-                }
-
-                tmp.add(item);
-                position++;
-            }
-
-            result = tmp;
+            result = new SubSequence(fromInclusive, toExclusive, seq);
         }
 
         if (context.getProfiler().isEnabled()) {

diff --git a/test/src/org/exist/xquery/functions/fn/FunSubSequenceTest.java b/test/src/org/exist/xquery/functions/fn/FunSubSequenceTest.java
@@ -156,6 +156,18 @@ public void smallPartOfLargeRange_arity3() throws XMLDBException {
         assertEquals("(2999999995,2999999996,2999999997,2999999998,2999999999)", asSequenceStr(result));
     }
 
+    @Test
+    public void largeRange_arity2() throws XMLDBException {
+        final ResourceSet result = existEmbeddedServer.executeQuery("fn:count(fn:subsequence((1 to 3000000000), -2147483649))");
+        assertEquals("(3000000000)", asSequenceStr(result));
+    }
+
+    @Test
+    public void largeRange_arity3() throws XMLDBException {
+        final ResourceSet result = existEmbeddedServer.executeQuery("fn:count(fn:subsequence((1 to 3000000000), 1, 3000000000))");
+        assertEquals("(3000000000)", asSequenceStr(result));
+    }
+
     private static String asSequenceStr(final ResourceSet result) throws XMLDBException {
         final StringBuilder builder = new StringBuilder();
         builder.append('(');