https://openjdk.java.net/ 
/*
 * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
 */
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.sun.org.apache.bcel.internal.util;

import com.sun.org.apache.bcel.internal.Const;
import com.sun.org.apache.bcel.internal.generic.ClassGenException;
import com.sun.org.apache.bcel.internal.generic.InstructionHandle;
import com.sun.org.apache.bcel.internal.generic.InstructionList;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;


InstructionFinder is a tool to search for given instructions patterns, i.e.,
match sequences of instructions in an instruction list via regular
expressions. This can be used, e.g., in order to implement a peep hole
optimizer that looks for code patterns and replaces them with faster
equivalents.


This class internally uses the java.util.regex
package to search for regular expressions.
A typical application would look like this:

  InstructionFinder f   = new InstructionFinder(il);
  String            pat = "IfInstruction ICONST_0 GOTO ICONST_1 NOP (IFEQ|IFNE)";
  for (Iterator i = f.search(pat, constraint); i.hasNext(); ) {
  InstructionHandle[] match = (InstructionHandle[])i.next();
  ...
  il.delete(match[1], match[5]);
  ...
  }



See Also:
Version:$Id: InstructionFinder.java 1749603 2016-06-21 20:50:19Z ggregory $
@LastModified: Oct 2017
/**
 * InstructionFinder is a tool to search for given instructions patterns, i.e.,
 * match sequences of instructions in an instruction list via regular
 * expressions. This can be used, e.g., in order to implement a peep hole
 * optimizer that looks for code patterns and replaces them with faster
 * equivalents.
 *
 * <p>
 * This class internally uses the java.util.regex
 * package to search for regular expressions.
 *
 * A typical application would look like this:
 *
 * <pre>
 *
 *
 *   InstructionFinder f   = new InstructionFinder(il);
 *   String            pat = &quot;IfInstruction ICONST_0 GOTO ICONST_1 NOP (IFEQ|IFNE)&quot;;
 *
 *   for (Iterator i = f.search(pat, constraint); i.hasNext(); ) {
 *   InstructionHandle[] match = (InstructionHandle[])i.next();
 *   ...
 *   il.delete(match[1], match[5]);
 *   ...
 *   }
 *
 *
 * </pre>
 *
 * @version $Id: InstructionFinder.java 1749603 2016-06-21 20:50:19Z ggregory $
 * @see com.sun.org.apache.bcel.internal.generic.Instruction
 * @see InstructionList
 * @LastModified: Oct 2017
 */
public class InstructionFinder {

    private static final int OFFSET = 32767; // char + OFFSET is outside of LATIN-1
    private static final int NO_OPCODES = 256; // Potential number, some are not used
    private static final Map<String, String> map = new HashMap<>();
    private final InstructionList il;
    private String il_string; // instruction list as string
    private InstructionHandle[] handles; // map instruction


    // list to array
    
Params:
  • il – 
         instruction list to search for given patterns
/**
     * @param il
     *          instruction list to search for given patterns
     */
    public InstructionFinder(final InstructionList il) {
        this.il = il;
        reread();
    }


    
Reread the instruction list, e.g., after you've altered the list upon a
match.

/**
     * Reread the instruction list, e.g., after you've altered the list upon a
     * match.
     */
    public final void reread() {
        final int size = il.getLength();
        final char[] buf = new char[size]; // Create a string with length equal to il length
        handles = il.getInstructionHandles();
        // Map opcodes to characters
        for (int i = 0; i < size; i++) {
            buf[i] = makeChar(handles[i].getInstruction().getOpcode());
        }
        il_string = new String(buf);
    }


    
Map symbolic instruction names like "getfield" to a single character.

Params:
  • pattern – 
         instruction pattern in lower case
Returns:encoded string for a pattern such as "BranchInstruction".
/**
     * Map symbolic instruction names like "getfield" to a single character.
     *
     * @param pattern
     *          instruction pattern in lower case
     * @return encoded string for a pattern such as "BranchInstruction".
     */
    private static String mapName( final String pattern ) {
        final String result = map.get(pattern);
        if (result != null) {
            return result;
        }
        for (short i = 0; i < NO_OPCODES; i++) {
            if (pattern.equals(Const.getOpcodeName(i))) {
                return "" + makeChar(i);
            }
        }
        throw new RuntimeException("Instruction unknown: " + pattern);
    }


    
Replace symbolic names of instructions with the appropiate character and
remove all white space from string. Meta characters such as +, * are
ignored.

Params:
  • pattern – 
         The pattern to compile
Returns:translated regular expression string
/**
     * Replace symbolic names of instructions with the appropiate character and
     * remove all white space from string. Meta characters such as +, * are
     * ignored.
     *
     * @param pattern
     *          The pattern to compile
     * @return translated regular expression string
     */
    private static String compilePattern( final String pattern ) {
        //Bug: BCEL-77 - Instructions are assumed to be english, to avoid odd Locale issues
        final String lower = pattern.toLowerCase(Locale.ENGLISH);
        final StringBuilder buf = new StringBuilder();
        final int size = pattern.length();
        for (int i = 0; i < size; i++) {
            char ch = lower.charAt(i);
            if (Character.isLetterOrDigit(ch)) {
                final StringBuilder name = new StringBuilder();
                while ((Character.isLetterOrDigit(ch) || ch == '_') && i < size) {
                    name.append(ch);
                    if (++i < size) {
                        ch = lower.charAt(i);
                    } else {
                        break;
                    }
                }
                i--;
                buf.append(mapName(name.toString()));
            } else if (!Character.isWhitespace(ch)) {
                buf.append(ch);
            }
        }
        return buf.toString();
    }


    
Returns:the matched piece of code as an array of instruction (handles)
/**
     * @return the matched piece of code as an array of instruction (handles)
     */
    private InstructionHandle[] getMatch( final int matched_from, final int match_length ) {
        final InstructionHandle[] match = new InstructionHandle[match_length];
        System.arraycopy(handles, matched_from, match, 0, match_length);
        return match;
    }


    
Search for the given pattern in the instruction list. You can search for
any valid opcode via its symbolic name, e.g. "istore". You can also use a
super class or an interface name to match a whole set of instructions, e.g.
"BranchInstruction" or "LoadInstruction". "istore" is also an alias for all
"istore_x" instructions. Additional aliases are "if" for "ifxx", "if_icmp"
for "if_icmpxx", "if_acmp" for "if_acmpxx".
Consecutive instruction names must be separated by white space which will
be removed during the compilation of the pattern.
For the rest the usual pattern matching rules for regular expressions
apply.


Example pattern:

search("BranchInstruction NOP ((IfInstruction|GOTO)+ ISTORE Instruction)*");




If you alter the instruction list upon a match such that other matching
areas are affected, you should call reread() to update the finder and call
search() again, because the matches are cached.

Params:
  • pattern – 
         the instruction pattern to search for, where case is ignored
  • from – 
         where to start the search in the instruction list
  • constraint – 
         optional CodeConstraint to check the found code pattern for
         user-defined constraints
Returns:iterator of matches where e.nextElement() returns an array of
        instruction handles describing the matched area
/**
     * Search for the given pattern in the instruction list. You can search for
     * any valid opcode via its symbolic name, e.g. "istore". You can also use a
     * super class or an interface name to match a whole set of instructions, e.g.
     * "BranchInstruction" or "LoadInstruction". "istore" is also an alias for all
     * "istore_x" instructions. Additional aliases are "if" for "ifxx", "if_icmp"
     * for "if_icmpxx", "if_acmp" for "if_acmpxx".
     *
     * Consecutive instruction names must be separated by white space which will
     * be removed during the compilation of the pattern.
     *
     * For the rest the usual pattern matching rules for regular expressions
     * apply.
     * <P>
     * Example pattern:
     *
     * <pre>
     * search(&quot;BranchInstruction NOP ((IfInstruction|GOTO)+ ISTORE Instruction)*&quot;);
     * </pre>
     *
     * <p>
     * If you alter the instruction list upon a match such that other matching
     * areas are affected, you should call reread() to update the finder and call
     * search() again, because the matches are cached.
     *
     * @param pattern
     *          the instruction pattern to search for, where case is ignored
     * @param from
     *          where to start the search in the instruction list
     * @param constraint
     *          optional CodeConstraint to check the found code pattern for
     *          user-defined constraints
     * @return iterator of matches where e.nextElement() returns an array of
     *         instruction handles describing the matched area
     */
    public final Iterator<InstructionHandle[]> search( final String pattern,
            final InstructionHandle from, final CodeConstraint constraint ) {
        final String search = compilePattern(pattern);
        int start = -1;
        for (int i = 0; i < handles.length; i++) {
            if (handles[i] == from) {
                start = i; // Where to start search from (index)
                break;
            }
        }
        if (start == -1) {
            throw new ClassGenException("Instruction handle " + from
                    + " not found in instruction list.");
        }
        final Pattern regex = Pattern.compile(search);
        final List<InstructionHandle[]> matches = new ArrayList<>();
        final Matcher matcher = regex.matcher(il_string);
        while (start < il_string.length() && matcher.find(start)) {
            final int startExpr = matcher.start();
            final int endExpr = matcher.end();
            final int lenExpr = endExpr - startExpr;
            final InstructionHandle[] match = getMatch(startExpr, lenExpr);
            if ((constraint == null) || constraint.checkCode(match)) {
                matches.add(match);
            }
            start = endExpr;
        }
        return matches.iterator();
    }


    
Start search beginning from the start of the given instruction list.

Params:
  • pattern – 
         the instruction pattern to search for, where case is ignored
Returns:iterator of matches where e.nextElement() returns an array of
        instruction handles describing the matched area
/**
     * Start search beginning from the start of the given instruction list.
     *
     * @param pattern
     *          the instruction pattern to search for, where case is ignored
     * @return iterator of matches where e.nextElement() returns an array of
     *         instruction handles describing the matched area
     */
    public final Iterator<InstructionHandle[]> search( final String pattern ) {
        return search(pattern, il.getStart(), null);
    }


    
Start search beginning from `from'.

Params:
  • pattern – 
         the instruction pattern to search for, where case is ignored
  • from – 
         where to start the search in the instruction list
Returns:iterator of matches where e.nextElement() returns an array of
        instruction handles describing the matched area
/**
     * Start search beginning from `from'.
     *
     * @param pattern
     *          the instruction pattern to search for, where case is ignored
     * @param from
     *          where to start the search in the instruction list
     * @return iterator of matches where e.nextElement() returns an array of
     *         instruction handles describing the matched area
     */
    public final Iterator<InstructionHandle[]> search( final String pattern,
            final InstructionHandle from ) {
        return search(pattern, from, null);
    }


    
Start search beginning from the start of the given instruction list. Check
found matches with the constraint object.

Params:
  • pattern – 
         the instruction pattern to search for, case is ignored
  • constraint – 
         constraints to be checked on matching code
Returns:instruction handle or `null' if the match failed
/**
     * Start search beginning from the start of the given instruction list. Check
     * found matches with the constraint object.
     *
     * @param pattern
     *          the instruction pattern to search for, case is ignored
     * @param constraint
     *          constraints to be checked on matching code
     * @return instruction handle or `null' if the match failed
     */
    public final Iterator<InstructionHandle[]> search( final String pattern,
            final CodeConstraint constraint ) {
        return search(pattern, il.getStart(), constraint);
    }


    
Convert opcode number to char.

/**
     * Convert opcode number to char.
     */
    private static char makeChar( final short opcode ) {
        return (char) (opcode + OFFSET);
    }


    
Returns:the inquired instruction list
/**
     * @return the inquired instruction list
     */
    public final InstructionList getInstructionList() {
        return il;
    }

    
Code patterns found may be checked using an additional user-defined
constraint object whether they really match the needed criterion. I.e.,
check constraints that can not expressed with regular expressions.

/**
     * Code patterns found may be checked using an additional user-defined
     * constraint object whether they really match the needed criterion. I.e.,
     * check constraints that can not expressed with regular expressions.
     *
     */
    public interface CodeConstraint {

        
Params:
  • match – 
         array of instructions matching the requested pattern
Returns:true if the matched area is really useful
/**
         * @param match
         *          array of instructions matching the requested pattern
         * @return true if the matched area is really useful
         */
        boolean checkCode( InstructionHandle[] match );
    }

    // Initialize pattern map
    static {
        map.put("arithmeticinstruction","(irem|lrem|iand|ior|ineg|isub|lneg|fneg|fmul|ldiv|fadd|lxor|frem|idiv|land|ixor|ishr|fsub|lshl|fdiv|iadd|lor|dmul|lsub|ishl|imul|lmul|lushr|dneg|iushr|lshr|ddiv|drem|dadd|ladd|dsub)");
        map.put("invokeinstruction", "(invokevirtual|invokeinterface|invokestatic|invokespecial|invokedynamic)");
        map.put("arrayinstruction", "(baload|aastore|saload|caload|fastore|lastore|iaload|castore|iastore|aaload|bastore|sastore|faload|laload|daload|dastore)");
        map.put("gotoinstruction", "(goto|goto_w)");
        map.put("conversioninstruction", "(d2l|l2d|i2s|d2i|l2i|i2b|l2f|d2f|f2i|i2d|i2l|f2d|i2c|f2l|i2f)");
        map.put("localvariableinstruction","(fstore|iinc|lload|dstore|dload|iload|aload|astore|istore|fload|lstore)");
        map.put("loadinstruction", "(fload|dload|lload|iload|aload)");
        map.put("fieldinstruction", "(getfield|putstatic|getstatic|putfield)");
        map.put("cpinstruction", "(ldc2_w|invokeinterface|invokedynamic|multianewarray|putstatic|instanceof|getstatic|checkcast|getfield|invokespecial|ldc_w|invokestatic|invokevirtual|putfield|ldc|new|anewarray)");
        map.put("stackinstruction", "(dup2|swap|dup2_x2|pop|pop2|dup|dup2_x1|dup_x2|dup_x1)");
        map.put("branchinstruction", "(ifle|if_acmpne|if_icmpeq|if_acmpeq|ifnonnull|goto_w|iflt|ifnull|if_icmpne|tableswitch|if_icmple|ifeq|if_icmplt|jsr_w|if_icmpgt|ifgt|jsr|goto|ifne|ifge|lookupswitch|if_icmpge)");
        map.put("returninstruction", "(lreturn|ireturn|freturn|dreturn|areturn|return)");
        map.put("storeinstruction", "(istore|fstore|dstore|astore|lstore)");
        map.put("select", "(tableswitch|lookupswitch)");
        map.put("ifinstruction", "(ifeq|ifgt|if_icmpne|if_icmpeq|ifge|ifnull|ifne|if_icmple|if_icmpge|if_acmpeq|if_icmplt|if_acmpne|ifnonnull|iflt|if_icmpgt|ifle)");
        map.put("jsrinstruction", "(jsr|jsr_w)");
        map.put("variablelengthinstruction", "(tableswitch|jsr|goto|lookupswitch)");
        map.put("unconditionalbranch", "(goto|jsr|jsr_w|athrow|goto_w)");
        map.put("constantpushinstruction", "(dconst|bipush|sipush|fconst|iconst|lconst)");
        map.put("typedinstruction", "(imul|lsub|aload|fload|lor|new|aaload|fcmpg|iand|iaload|lrem|idiv|d2l|isub|dcmpg|dastore|ret|f2d|f2i|drem|iinc|i2c|checkcast|frem|lreturn|astore|lushr|daload|dneg|fastore|istore|lshl|ldiv|lstore|areturn|ishr|ldc_w|invokeinterface|invokedynamic|aastore|lxor|ishl|l2d|i2f|return|faload|sipush|iushr|caload|instanceof|invokespecial|putfield|fmul|ireturn|laload|d2f|lneg|ixor|i2l|fdiv|lastore|multianewarray|i2b|getstatic|i2d|putstatic|fcmpl|saload|ladd|irem|dload|jsr_w|dconst|dcmpl|fsub|freturn|ldc|aconst_null|castore|lmul|ldc2_w|dadd|iconst|f2l|ddiv|dstore|land|jsr|anewarray|dmul|bipush|dsub|sastore|d2i|i2s|lshr|iadd|l2i|lload|bastore|fstore|fneg|iload|fadd|baload|fconst|ior|ineg|dreturn|l2f|lconst|getfield|invokevirtual|invokestatic|iastore)");
        map.put("popinstruction", "(fstore|dstore|pop|pop2|astore|putstatic|istore|lstore)");
        map.put("allocationinstruction", "(multianewarray|new|anewarray|newarray)");
        map.put("indexedinstruction", "(lload|lstore|fload|ldc2_w|invokeinterface|invokedynamic|multianewarray|astore|dload|putstatic|instanceof|getstatic|checkcast|getfield|invokespecial|dstore|istore|iinc|ldc_w|ret|fstore|invokestatic|iload|putfield|invokevirtual|ldc|new|aload|anewarray)");
        map.put("pushinstruction", "(dup|lload|dup2|bipush|fload|ldc2_w|sipush|lconst|fconst|dload|getstatic|ldc_w|aconst_null|dconst|iload|ldc|iconst|aload)");
        map.put("stackproducer", "(imul|lsub|aload|fload|lor|new|aaload|fcmpg|iand|iaload|lrem|idiv|d2l|isub|dcmpg|dup|f2d|f2i|drem|i2c|checkcast|frem|lushr|daload|dneg|lshl|ldiv|ishr|ldc_w|invokeinterface|invokedynamic|lxor|ishl|l2d|i2f|faload|sipush|iushr|caload|instanceof|invokespecial|fmul|laload|d2f|lneg|ixor|i2l|fdiv|getstatic|i2b|swap|i2d|dup2|fcmpl|saload|ladd|irem|dload|jsr_w|dconst|dcmpl|fsub|ldc|arraylength|aconst_null|tableswitch|lmul|ldc2_w|iconst|dadd|f2l|ddiv|land|jsr|anewarray|dmul|bipush|dsub|d2i|newarray|i2s|lshr|iadd|lload|l2i|fneg|iload|fadd|baload|fconst|lookupswitch|ior|ineg|lconst|l2f|getfield|invokevirtual|invokestatic)");
        map.put("stackconsumer", "(imul|lsub|lor|iflt|fcmpg|if_icmpgt|iand|ifeq|if_icmplt|lrem|ifnonnull|idiv|d2l|isub|dcmpg|dastore|if_icmpeq|f2d|f2i|drem|i2c|checkcast|frem|lreturn|astore|lushr|pop2|monitorexit|dneg|fastore|istore|lshl|ldiv|lstore|areturn|if_icmpge|ishr|monitorenter|invokeinterface|invokedynamic|aastore|lxor|ishl|l2d|i2f|return|iushr|instanceof|invokespecial|fmul|ireturn|d2f|lneg|ixor|pop|i2l|ifnull|fdiv|lastore|i2b|if_acmpeq|ifge|swap|i2d|putstatic|fcmpl|ladd|irem|dcmpl|fsub|freturn|ifgt|castore|lmul|dadd|f2l|ddiv|dstore|land|if_icmpne|if_acmpne|dmul|dsub|sastore|ifle|d2i|i2s|lshr|iadd|l2i|bastore|fstore|fneg|fadd|ior|ineg|ifne|dreturn|l2f|if_icmple|getfield|invokevirtual|invokestatic|iastore)");
        map.put("exceptionthrower","(irem|lrem|laload|putstatic|baload|dastore|areturn|getstatic|ldiv|anewarray|iastore|castore|idiv|saload|lastore|fastore|putfield|lreturn|caload|getfield|return|aastore|freturn|newarray|instanceof|multianewarray|athrow|faload|iaload|aaload|dreturn|monitorenter|checkcast|bastore|arraylength|new|invokevirtual|sastore|ldc_w|ireturn|invokespecial|monitorexit|invokeinterface|invokedynamic|ldc|invokestatic|daload)");
        map.put("loadclass", "(multianewarray|invokeinterface|invokedynamic|instanceof|invokespecial|putfield|checkcast|putstatic|invokevirtual|new|getstatic|invokestatic|getfield|anewarray)");
        map.put("instructiontargeter", "(ifle|if_acmpne|if_icmpeq|if_acmpeq|ifnonnull|goto_w|iflt|ifnull|if_icmpne|tableswitch|if_icmple|ifeq|if_icmplt|jsr_w|if_icmpgt|ifgt|jsr|goto|ifne|ifge|lookupswitch|if_icmpge)");
        // Some aliases
        map.put("if_icmp", "(if_icmpne|if_icmpeq|if_icmple|if_icmpge|if_icmplt|if_icmpgt)");
        map.put("if_acmp", "(if_acmpeq|if_acmpne)");
        map.put("if", "(ifeq|ifne|iflt|ifge|ifgt|ifle)");
        // Precompile some aliases first
        map.put("iconst", precompile(Const.ICONST_0, Const.ICONST_5, Const.ICONST_M1));
        map.put("lconst", new String(new char[] { '(', makeChar(Const.LCONST_0), '|', makeChar(Const.LCONST_1), ')' }));
        map.put("dconst", new String(new char[] { '(', makeChar(Const.DCONST_0), '|', makeChar(Const.DCONST_1), ')' }));
        map.put("fconst", new String(new char[] { '(', makeChar(Const.FCONST_0), '|', makeChar(Const.FCONST_1), '|', makeChar(Const.FCONST_2), ')' }));
        map.put("lload", precompile(Const.LLOAD_0, Const.LLOAD_3, Const.LLOAD));
        map.put("iload", precompile(Const.ILOAD_0, Const.ILOAD_3, Const.ILOAD));
        map.put("dload", precompile(Const.DLOAD_0, Const.DLOAD_3, Const.DLOAD));
        map.put("fload", precompile(Const.FLOAD_0, Const.FLOAD_3, Const.FLOAD));
        map.put("aload", precompile(Const.ALOAD_0, Const.ALOAD_3, Const.ALOAD));
        map.put("lstore", precompile(Const.LSTORE_0, Const.LSTORE_3, Const.LSTORE));
        map.put("istore", precompile(Const.ISTORE_0, Const.ISTORE_3, Const.ISTORE));
        map.put("dstore", precompile(Const.DSTORE_0, Const.DSTORE_3, Const.DSTORE));
        map.put("fstore", precompile(Const.FSTORE_0, Const.FSTORE_3, Const.FSTORE));
        map.put("astore", precompile(Const.ASTORE_0, Const.ASTORE_3, Const.ASTORE));
        // Compile strings
        for (final Map.Entry<String, String> entry : map.entrySet()) {
            final String key = entry.getKey();
            final String value = entry.getValue();
            final char ch = value.charAt(1); // Omit already precompiled patterns
            if (ch < OFFSET) {
                map.put(key, compilePattern(value)); // precompile all patterns
            }
        }
        // Add instruction alias to match anything
        final StringBuilder buf = new StringBuilder("(");
        for (short i = 0; i < NO_OPCODES; i++) {
            if (Const.getNoOfOperands(i) != Const.UNDEFINED) { // Not an invalid opcode
                buf.append(makeChar(i));
                if (i < NO_OPCODES - 1) {
                    buf.append('|');
                }
            }
        }
        buf.append(')');
        map.put("instruction", buf.toString());
    }


    private static String precompile( final short from, final short to, final short extra ) {
        final StringBuilder buf = new StringBuilder("(");
        for (short i = from; i <= to; i++) {
            buf.append(makeChar(i));
            buf.append('|');
        }
        buf.append(makeChar(extra));
        buf.append(")");
        return buf.toString();
    }


    /*
     * Internal debugging routines.
     */
//    private static final String pattern2string( String pattern ) {
//        return pattern2string(pattern, true);
//    }


//    private static final String pattern2string( String pattern, boolean make_string ) {
//        StringBuffer buf = new StringBuffer();
//        for (int i = 0; i < pattern.length(); i++) {
//            char ch = pattern.charAt(i);
//            if (ch >= OFFSET) {
//                if (make_string) {
//                    buf.append(Constants.getOpcodeName(ch - OFFSET));
//                } else {
//                    buf.append((ch - OFFSET));
//                }
//            } else {
//                buf.append(ch);
//            }
//        }
//        return buf.toString();
//    }
}