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[6.x.x] Optimize fn:reverse by removing unnecessary work #91

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Merged
adamretter merged 2 commits into from
Sep 2, 2025
Merged

[6.x.x] Optimize fn:reverse by removing unnecessary work #91

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4ab9ade
[optimise] Avoid unnecessary double iteration in fn:reverse
adamretter Feb 10, 2025
52df743
[refactor] Simplify the code in fn:reverse
adamretter Sep 2, 2025
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2 changes: 1 addition & 1 deletion exist-core/src/main/java/org/exist/xquery/functions/fn/FnModule.java
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Original file line number Diff line number Diff line change
Expand Up @@ -210,7 +210,7 @@ public class FnModule extends AbstractInternalModule {
new FunctionDef(FunRemove.signature, FunRemove.class),
new FunctionDef(FunReplace.FS_REPLACE[0], FunReplace.class),
new FunctionDef(FunReplace.FS_REPLACE[1], FunReplace.class),
new FunctionDef(FunReverse.signature, FunReverse.class),
new FunctionDef(FunReverse.FS_REVERSE, FunReverse.class),
new FunctionDef(FunResolveURI.signatures[0], FunResolveURI.class),
new FunctionDef(FunResolveURI.signatures[1], FunResolveURI.class),
new FunctionDef(FunRoot.signatures[0], FunRoot.class),
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108 changes: 31 additions & 77 deletions exist-core/src/main/java/org/exist/xquery/functions/fn/FunReverse.java
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Original file line number Diff line number Diff line change
Expand Up @@ -45,95 +45,49 @@
*/
package org.exist.xquery.functions.fn;

import org.exist.dom.QName;
import org.exist.xquery.*;
import org.exist.xquery.value.FunctionParameterSequenceType;
import org.exist.xquery.value.FunctionReturnSequenceType;
import org.exist.xquery.value.Item;
import org.exist.xquery.BasicFunction;
import org.exist.xquery.FunctionSignature;
import org.exist.xquery.XPathException;
import org.exist.xquery.XQueryContext;
import org.exist.xquery.value.Sequence;
import org.exist.xquery.value.SequenceIterator;
import org.exist.xquery.value.SequenceType;
import org.exist.xquery.value.Type;
import org.exist.xquery.value.ValueSequence;
import org.exist.xquery.value.Type;

import static org.exist.xquery.FunctionDSL.optManyParam;
import static org.exist.xquery.FunctionDSL.returnsOptMany;
import static org.exist.xquery.functions.fn.FnModule.functionSignature;

/**
* Implements the fn:reverse function.
*
* @author <a href="mailto:piotr@ideanest.com">Piotr Kaminski</a>
* @author <a href="mailto:adam@evolvedbinary.com">Adam Retter</a>
*/
public class FunReverse extends Function {
public class FunReverse extends BasicFunction {

public final static FunctionSignature signature =
new FunctionSignature(
new QName("reverse", FnModule.NAMESPACE_URI),
"Reverses the order of items in a sequence. If the argument is an empty" +
"sequence, the empty sequence is returned.",
new SequenceType[] {new FunctionParameterSequenceType("arg", Type.ITEM, Cardinality.ZERO_OR_MORE, "The sequence to reverse")},
new FunctionReturnSequenceType(Type.ITEM, Cardinality.ZERO_OR_MORE, "the reverse order sequence"));
public static final FunctionSignature FS_REVERSE = functionSignature(
"reverse",
"Reverses the order of items in a sequence. If the argument is an empty sequence, the empty sequence is returned.",
returnsOptMany(Type.ITEM, "The reverse order sequence"),
optManyParam("arg", Type.ITEM, "The sequence to reverse")
);

public FunReverse(XQueryContext context) {
super(context, signature);
}

public void analyze(final AnalyzeContextInfo contextInfo) throws XPathException {
inPredicate = (contextInfo.getFlags() & IN_PREDICATE) > 0;
contextId = contextInfo.getContextId();
contextInfo.setParent(this);

final SequenceType[] argumentTypes = getSignature().getArgumentTypes();
for (int i = 0; i < getArgumentCount(); i++) {
final Expression arg = getArgument(i);

// call analyze for each argument
final AnalyzeContextInfo argContextInfo = new AnalyzeContextInfo(contextInfo);
arg.analyze(argContextInfo);
if (i == 0) {
contextInfo.setStaticReturnType(argContextInfo.getStaticReturnType());
}

if (!argumentsChecked) {
// statically check the argument
SequenceType argType = null;
if (argumentTypes != null && i < argumentTypes.length) {
argType = argumentTypes[i];
}
checkArgument(arg, argType, argContextInfo, i + 1);
}
}
argumentsChecked = true;
public FunReverse(final XQueryContext context, final FunctionSignature signature) {
super(context, signature);
}

public Sequence eval(Sequence contextSequence, Item contextItem) throws XPathException {
if (context.getProfiler().isEnabled()) {
context.getProfiler().start(this);
context.getProfiler().message(this, Profiler.DEPENDENCIES, "DEPENDENCIES", Dependency.getDependenciesName(this.getDependencies()));
if (contextSequence != null)
{context.getProfiler().message(this, Profiler.START_SEQUENCES, "CONTEXT SEQUENCE", contextSequence);}
if (contextItem != null)
{context.getProfiler().message(this, Profiler.START_SEQUENCES, "CONTEXT ITEM", contextItem.toSequence());}
}

Sequence result;
final Sequence seq = getArguments(contextSequence, contextItem)[0];
if (seq.isEmpty())
{result = Sequence.EMPTY_SEQUENCE;}
else {
final Sequence tmp = new ValueSequence();
Item item;
for(final SequenceIterator i = seq.iterate(); i.hasNext(); ) {
item = i.nextItem();
tmp.add(item);
}
result = new ValueSequence();
for (int i = seq.getItemCount() - 1; i >= 0; i--) {
result.add(tmp.itemAt(i));
}
@Override
public Sequence eval(final Sequence[] args, final Sequence contextSequence) throws XPathException {
final Sequence seq = args[0];
final Sequence result;
if (seq.isEmpty()) {
result = Sequence.EMPTY_SEQUENCE;
} else {
result = new ValueSequence();
for (int i = seq.getItemCount() - 1; i >= 0; i--) {
result.add(seq.itemAt(i));
}
}

if (context.getProfiler().isEnabled())
{context.getProfiler().end(this, "", result);}

return result;
}

}
}