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The ucar.units Java package is for decoding and encoding formatted unit specifications (e.g. "m/s"), converting numeric values between compatible units (e.g. between "m/s" and "knot"), and for performing arithmetic operations on units (e.g. dividing one unit by another, or raising a unit to a power).
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/*
* Copyright (c) 1998-2018 University Corporation for Atmospheric Research/Unidata
* See LICENSE for license information.
*/
package ucar.units;
import javax.annotation.concurrent.Immutable;
/**
* Provides support for units that are based on a logarithm of the ratio of a
* physical quantity to an underlying reference level.
*
* Instances of this class are immutable.
*
* @author Steven R. Emmerson
*/
@Immutable
public final class LogarithmicUnit extends UnitImpl implements DerivableUnit {
private static final long serialVersionUID = 1L;
/**
* The logarithmic base.
*
* @serial
*/
private final double base;
private final transient double lnBase;
/**
* The reference level.
*
* @serial
*/
private final DerivableUnit reference;
private final transient DerivedUnit derivedUnit;
/**
* Constructs from a reference level and a logarithmic base.
*
* @param reference
* The reference level. Must be a {@link DerivableUnit}.
* @param base
* The logarithmic base. Must be 2, {@link Math#E}, or 10.
* @throws IllegalArgumentException
* if {@code reference} isn't a {@link DerivableUnit}.
* @throws IllegalArgumentException
* if {@code base} isn't one of the allowed values.
* @throws NullPointerException
* if {@code reference} is {@code null}.
*/
public LogarithmicUnit(final Unit reference, final double base) {
this(reference, base, null);
}
/**
* Constructs from a reference level, a logarithmic base, and a unit
* identifier.
*
* @param reference
* The reference level. Must be a {@link DerivableUnit}.
* @param base
* The logarithmic base. Must be 2, {@link Math#E}, or 10.
* @param id
* The identifier for the new unit.
* @throws IllegalArgumentException
* if {@code reference} isn't a {@link DerivableUnit}.
* @throws IllegalArgumentException
* if {@code base} isn't one of the allowed values.
* @throws NullPointerException
* if {@code reference} is {@code null}.
*/
public LogarithmicUnit(final Unit reference, final double base,
final UnitName id) {
super(id);
if (reference == null) {
throw new NullPointerException("Null reference argument");
}
if (!(reference instanceof DerivableUnit)) {
throw new IllegalArgumentException("Not a DerivableUnit: "
+ reference);
}
this.reference = (DerivableUnit) reference;
if (base != 2 && base != 10 && base != Math.E) {
throw new IllegalArgumentException("Invalid base: " + base);
}
this.base = base;
lnBase = base == Math.E
? 1
: Math.log(base);
derivedUnit = reference.getDerivedUnit();
}
static Unit getInstance(final Unit unit, final double base) {
return new LogarithmicUnit(unit, base);
}
/**
* Returns the reference level.
*
* @return The reference level.
*/
public DerivableUnit getReference() {
return reference;
}
/**
* Returns the logarithmic base.
*
* @return The logarithmic base of this unit.
*/
public double getBase() {
return base;
}
/*
* From UnitImpl:
*/
/**
* Clones this unit, changing the identifier.
*
* @param id
* The identifier for the new unit.
* @return This unit with its identifier changed.
*/
public Unit clone(final UnitName id) {
return new LogarithmicUnit((Unit) reference, getBase(), id);
}
/**
* Multiply this unit by another unit.
*
* @param that
* The unit to multiply this unit by. Must be dimensionless.
* @return The product of this unit and that.
* @throws MultiplyException
* Can't multiply these units together.
*/
@Override
protected Unit myMultiplyBy(final Unit that) throws MultiplyException {
if (!that.isDimensionless()) {
throw new MultiplyException(that);
}
return that instanceof ScaledUnit
? new ScaledUnit(((ScaledUnit) that).getScale(), this)
: this;
}
/**
* Divide this unit by another unit.
*
* @param that
* The unit to divide this unit by.
* @return The quotient of this unit and that.
* @throws DivideException
* Can't divide these units.
*/
@Override
protected Unit myDivideBy(final Unit that) throws DivideException {
if (!that.isDimensionless()) {
throw new DivideException(that);
}
return that instanceof ScaledUnit
? new ScaledUnit(1.0 / ((ScaledUnit) that).getScale(), this)
: this;
}
/**
* Divide this unit into another unit.
*
* @param that
* The unit to divide this unit into.
* @return The quotient of that unit and this unit.
* @throws DivideException
* Can't divide these units.
*/
@Override
protected Unit myDivideInto(final Unit that) throws OperationException {
throw new DivideException(that);
}
/**
* Raise this unit to a power.
*
* @param power
* The power to raise this unit by. The only meaningful values
* are 0 and 1.
* @return The result of raising this unit by the power power.
* @throws RaiseException
* Can't raise this unit to {@code power}, which is neither 0
* nor 1.
*/
@Override
protected Unit myRaiseTo(final int power) throws RaiseException {
if (power == 0) {
return DerivedUnitImpl.DIMENSIONLESS;
}
if (power == 1) {
return this;
}
throw new RaiseException(this);
}
/**
* Returns the derived unit that is convertible with this unit.
*
* @return The derived unit that is convertible with this unit.
*/
public DerivedUnit getDerivedUnit() {
return derivedUnit;
}
/**
* Converts a value in this unit to the equivalent value in the convertible
* derived unit.
*
* @param amount
* The value in this unit.
* @return The equivalent value in the convertible derived unit.
* @throws ConversionException
* Can't convert between units.
*/
public float toDerivedUnit(final float amount) throws ConversionException {
return (float) toDerivedUnit((double) amount);
}
/**
* Converts a value in this unit to the equivalent value in the convertible
* derived unit.
*
* @param amount
* The value in this unit.
* @return The equivalent value in the convertible derived unit.
* @throws ConversionException
* Can't convert between units.
*/
public double toDerivedUnit(final double amount) throws ConversionException {
return reference.toDerivedUnit(Math.exp(amount * lnBase));
}
/**
* Converts values in this unit to the equivalent values in the convertible
* derived unit.
*
* @param input
* The values in this unit.
* @param output
* The equivalent values in the convertible derived unit. May be
* the same array as input.
* @return output.
* @throws ConversionException
* Can't convert between units.
*/
public float[] toDerivedUnit(final float[] input, final float[] output)
throws ConversionException {
for (int i = input.length; --i >= 0;) {
output[i] = (float) (Math.exp(input[i] * lnBase));
}
return reference.toDerivedUnit(output, output);
}
/**
* Converts values in this unit to the equivalent values in the convertible
* derived unit.
*
* @param input
* The values in this unit.
* @param output
* The equivalent values in the convertible derived unit. May be
* the same array as input.
* @return output.
* @throws ConversionException
* Can't convert between units.
*/
public double[] toDerivedUnit(final double[] input, final double[] output)
throws ConversionException {
for (int i = input.length; --i >= 0;) {
output[i] = Math.exp(input[i] * lnBase);
}
return reference.toDerivedUnit(output, output);
}
/**
* Converts a value in the convertible derived unit to the equivalent value
* in this unit.
*
* @param amount
* The value in the convertible derived unit.
* @return The equivalent value in this unit.
* @throws ConversionException
* Can't convert between units.
*/
public float fromDerivedUnit(final float amount) throws ConversionException {
return (float) fromDerivedUnit((double) amount);
}
/**
* Converts a value in the convertible derived unit to the equivalent value
* in this unit.
*
* @param amount
* The value in the convertible derived unit.
* @return The equivalent value in this unit.
* @throws ConversionException
* Can't convert between units.
*/
public double fromDerivedUnit(final double amount)
throws ConversionException {
return Math.log(reference.fromDerivedUnit(amount)) / lnBase;
}
/**
* Converts values in the convertible derived unit to the equivalent values
* in this unit.
*
* @param input
* The values in the convertible derived unit.
* @param output
* The equivalent values in this unit. May be the same array as
* input.
* @return output.
* @throws ConversionException
* Can't convert between units.
*/
public float[] fromDerivedUnit(final float[] input, final float[] output)
throws ConversionException {
reference.fromDerivedUnit(input, output);
for (int i = input.length; --i >= 0;) {
output[i] = (float) (Math.log(output[i]) / lnBase);
}
return output;
}
/**
* Converts values in the convertible derived unit to the equivalent values
* in this unit.
*
* @param input
* The values in the convertible derived unit.
* @param output
* The equivalent values in this unit. May be the same array as
* input.
* @return output.
* @throws ConversionException
* Can't convert between units.
*/
public double[] fromDerivedUnit(final double[] input, final double[] output)
throws ConversionException {
reference.fromDerivedUnit(input, output);
for (int i = input.length; --i >= 0;) {
output[i] = (float) (Math.log(output[i]) / lnBase);
}
return output;
}
/**
* Indicates if this unit is semantically identical to an object.
*
* @param object
* The object.
* @return true if and only if this unit is semantically
* identical to object
* .
*/
@Override
public boolean equals(final Object object) {
if (this == object) {
return true;
}
if (!(object instanceof LogarithmicUnit)) {
return false;
}
final LogarithmicUnit that = (LogarithmicUnit) object;
return base == that.base && reference.equals(that.reference);
}
/**
* Returns the hash code of this instance.
*
* @return The hash code of this instance.
*/
@Override
public int hashCode() {
return Double.valueOf(base).hashCode() ^ getReference().hashCode();
}
/**
* Indicates if this unit is dimensionless.
*
* @return true, always.
*/
public boolean isDimensionless() {
return true;
}
/**
* Returns the string representation of this unit.
*
* @return The string representation of this unit.
*/
@Override
public String toString() {
final String string = super.toString(); // get symbol or name
return string != null
? string
: getCanonicalString();
}
/**
* Returns the canonical string representation of the unit.
*
* @return The canonical string representation.
*/
public String getCanonicalString() {
return (base == 2
? "lb"
: base == Math.E
? "ln"
: "lg") + "(re " + getReference().toString() + ")";
}
}