# PDFunctionType4.java

    /*
     * 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 org.apache.pdfbox.pdmodel.common.function;

    import org.apache.pdfbox.cos.COSBase;
    import org.apache.pdfbox.pdmodel.common.PDRange;
    import org.apache.pdfbox.pdmodel.common.function.type4.ExecutionContext;
    import org.apache.pdfbox.pdmodel.common.function.type4.InstructionSequence;
    import org.apache.pdfbox.pdmodel.common.function.type4.InstructionSequenceBuilder;
    import org.apache.pdfbox.pdmodel.common.function.type4.Operators;

    import java.io.IOException;
    import java.nio.charset.StandardCharsets;

    /**
     * This class represents a Type 4 (PostScript calculator) function in a PDF document.
     * <p>
     * See section 3.9.4 of the PDF 1.4 Reference.
     *
     */
    public class PDFunctionType4 extends PDFunction
    {

        private static final Operators OPERATORS = new Operators();

        private final InstructionSequence instructions;

        /**
         * Constructor.
         *
         * @param functionStream The function stream.
         * @throws IOException if an I/O error occurs while reading the function
         */
        public PDFunctionType4(COSBase functionStream) throws IOException
        {
            super( functionStream );
            byte[] bytes = getPDStream().toByteArray();
            String string = new String(bytes, StandardCharsets.ISO_8859_1);
            this.instructions = InstructionSequenceBuilder.parse(string);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int getFunctionType()
        {
            return 4;
        }

        /**
        * {@inheritDoc}
        */
        @Override
        public float[] eval(float[] input) throws IOException
        {
            //Setup the input values
            ExecutionContext context = new ExecutionContext(OPERATORS);
            for (int i = 0; i < input.length; i++)
            {
                PDRange domain = getDomainForInput(i);
                float value = clipToRange(input[i], domain.getMin(), domain.getMax());
                context.getStack().push(value);
            }

            //Execute the type 4 function.
            instructions.execute(context);

            //Extract the output values
            int numberOfOutputValues = getNumberOfOutputParameters();
            int numberOfActualOutputValues = context.getStack().size();
            if (numberOfActualOutputValues < numberOfOutputValues)
            {
                throw new IllegalStateException("The type 4 function returned "
                        + numberOfActualOutputValues
                        + " values but the Range entry indicates that "
                        + numberOfOutputValues + " values be returned.");
            }
            float[] outputValues = new float[numberOfOutputValues];
            for (int i = numberOfOutputValues - 1; i >= 0; i--)
            {
                PDRange range = getRangeForOutput(i);
                outputValues[i] = context.popReal();
                outputValues[i] = clipToRange(outputValues[i], range.getMin(), range.getMax());
            }

            //Return the resulting array
            return outputValues;
        }
    }