001/*
002 * Units of Measurement Reference Implementation
003 * Copyright (c) 2005-2020, Units of Measurement project.
004 *
005 * All rights reserved.
006 *
007 * Redistribution and use in source and binary forms, with or without modification,
008 * are permitted provided that the following conditions are met:
009 *
010 * 1. Redistributions of source code must retain the above copyright notice,
011 *    this list of conditions and the following disclaimer.
012 *
013 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions
014 *    and the following disclaimer in the documentation and/or other materials provided with the distribution.
015 *
016 * 3. Neither the name of JSR-385, Indriya nor the names of their contributors may be used to endorse or promote products
017 *    derived from this software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
020 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
021 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
022 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
023 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
026 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
028 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package tech.units.indriya.function;
031
032import java.util.Objects;
033
034import javax.measure.UnitConverter;
035
036import tech.units.indriya.internal.function.calc.Calculator;
037import tech.uom.lib.common.function.ValueSupplier;
038
039/**
040 * <p>
041 * This class represents a logarithmic converter of limited precision. Such converter is typically used to create logarithmic unit. For example:<code>
042 * Unit<Dimensionless> BEL = Unit.ONE.transform(new LogConverter(10).inverse()); </code>
043 *
044 * @author <a href="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a>
045 * @author <a href="mailto:werner@units.tech">Werner Keil</a>
046 * @author Andi Huber
047 * @version 1.2, Jun 21, 2019
048 * @since 1.0
049 */
050public final class LogConverter extends AbstractConverter implements ValueSupplier<String> { // implements
051        // Immutable<String>
052        // {
053
054        /**
055         * 
056         */
057        private static final long serialVersionUID = -7584688290961460870L;
058
059        /**
060         * Holds the logarithmic base.
061         */
062        private final double base;
063        /**
064         * Holds the natural logarithm of the base.
065         */
066        private final double logOfBase;
067
068        /**
069         * Returns a logarithmic converter having the specified base.
070         *
071         * @param base
072         *          the logarithmic base (e.g. <code>Math.E</code> for the Natural Logarithm).
073         */
074        public LogConverter(double base) {
075                this.base = base;
076                this.logOfBase = Math.log(base);
077        }
078
079        /**
080         * Returns the logarithmic base of this converter.
081         *
082         * @return the logarithmic base (e.g. <code>Math.E</code> for the Natural Logarithm).
083         */
084        public double getBase() {
085                return base;
086        }
087
088        @Override
089        public boolean isIdentity() {
090                return false;
091        }
092
093        @Override
094        protected boolean canReduceWith(AbstractConverter that) {
095                if(that instanceof ExpConverter) {
096                        return ((ExpConverter)that).getBase() == base; // can compose with exp to identity, provided it has same base
097                }
098                return false;
099        }
100
101        @Override
102        protected AbstractConverter reduce(AbstractConverter that) {
103                return AbstractConverter.IDENTITY;
104        }
105
106        @Override
107        public AbstractConverter inverseWhenNotIdentity() {
108                return new ExpConverter(base);
109        }
110
111        @Override
112        public final String transformationLiteral() {
113                if (base == Math.E) return "x -> ln(x)";
114                return String.format("x -> log(base=%s, x)", base);
115        }
116        
117        @Override
118        public boolean equals(Object obj) {
119                if (this == obj) {
120                        return true;
121                }
122                if (obj instanceof LogConverter) {
123                        LogConverter that = (LogConverter) obj;
124                        return Objects.equals(base, that.base);
125                }
126                return false;
127        }
128
129        @Override
130        public int hashCode() {
131                return Objects.hash(base);
132        }
133
134    @Override
135    protected Number convertWhenNotIdentity(Number value) {
136        return Calculator.of(value)
137              .log()
138              .divide(logOfBase)
139              .peek();
140    }
141
142        @Override
143        public boolean isLinear() {
144                return false;
145        }
146
147        @Override
148        public String getValue() {
149                return toString();
150        }
151
152        @Override
153        public int compareTo(UnitConverter o) {
154                if (this == o) {
155                        return 0;
156                }
157                if (o instanceof ValueSupplier) {
158                        return getValue().compareTo(String.valueOf(((ValueSupplier<?>) o).getValue()));
159                }
160                return -1;
161        }
162}