Java tutorial
//package com.java2s; /* * Copyright (c) 2003, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ import sun.misc.FloatConsts; import sun.misc.DoubleConsts; public class Main { /** * Returns unbiased exponent of a <code>double</code>; for * subnormal values, the number is treated as if it were * normalized. That is for all finite, non-zero, positive numbers * <i>x</i>, <code>scalb(<i>x</i>, -ilogb(<i>x</i>))</code> is * always in the range [1, 2). * <p> * Special cases: * <ul> * <li> If the argument is NaN, then the result is 2<sup>30</sup>. * <li> If the argument is infinite, then the result is 2<sup>28</sup>. * <li> If the argument is zero, then the result is -(2<sup>28</sup>). * </ul> * * @param d floating-point number whose exponent is to be extracted * @return unbiased exponent of the argument. * @author Joseph D. Darcy */ public static int ilogb(double d) { int exponent = getExponent(d); switch (exponent) { case DoubleConsts.MAX_EXPONENT + 1: // NaN or infinity if (isNaN(d)) return (1 << 30); // 2^30 else // infinite value return (1 << 28); // 2^28 // break; case DoubleConsts.MIN_EXPONENT - 1: // zero or subnormal if (d == 0.0) { return -(1 << 28); // -(2^28) } else { long transducer = Double.doubleToRawLongBits(d); /* * To avoid causing slow arithmetic on subnormals, * the scaling to determine when d's significand * is normalized is done in integer arithmetic. * (there must be at least one "1" bit in the * significand since zero has been screened out. */ // isolate significand bits transducer &= DoubleConsts.SIGNIF_BIT_MASK; assert (transducer != 0L); // This loop is simple and functional. We might be // able to do something more clever that was faster; // e.g. number of leading zero detection on // (transducer << (# exponent and sign bits). while (transducer < (1L << (DoubleConsts.SIGNIFICAND_WIDTH - 1))) { transducer *= 2; exponent--; } exponent++; assert (exponent >= DoubleConsts.MIN_EXPONENT - (DoubleConsts.SIGNIFICAND_WIDTH - 1) && exponent < DoubleConsts.MIN_EXPONENT); return exponent; } // break; default: assert (exponent >= DoubleConsts.MIN_EXPONENT && exponent <= DoubleConsts.MAX_EXPONENT); return exponent; // break; } } /** * Returns unbiased exponent of a <code>float</code>; for * subnormal values, the number is treated as if it were * normalized. That is for all finite, non-zero, positive numbers * <i>x</i>, <code>scalb(<i>x</i>, -ilogb(<i>x</i>))</code> is * always in the range [1, 2). * <p> * Special cases: * <ul> * <li> If the argument is NaN, then the result is 2<sup>30</sup>. * <li> If the argument is infinite, then the result is 2<sup>28</sup>. * <li> If the argument is zero, then the result is -(2<sup>28</sup>). * </ul> * * @param f floating-point number whose exponent is to be extracted * @return unbiased exponent of the argument. * @author Joseph D. Darcy */ public static int ilogb(float f) { int exponent = getExponent(f); switch (exponent) { case FloatConsts.MAX_EXPONENT + 1: // NaN or infinity if (isNaN(f)) return (1 << 30); // 2^30 else // infinite value return (1 << 28); // 2^28 // break; case FloatConsts.MIN_EXPONENT - 1: // zero or subnormal if (f == 0.0f) { return -(1 << 28); // -(2^28) } else { int transducer = Float.floatToRawIntBits(f); /* * To avoid causing slow arithmetic on subnormals, * the scaling to determine when f's significand * is normalized is done in integer arithmetic. * (there must be at least one "1" bit in the * significand since zero has been screened out. */ // isolate significand bits transducer &= FloatConsts.SIGNIF_BIT_MASK; assert (transducer != 0); // This loop is simple and functional. We might be // able to do something more clever that was faster; // e.g. number of leading zero detection on // (transducer << (# exponent and sign bits). while (transducer < (1 << (FloatConsts.SIGNIFICAND_WIDTH - 1))) { transducer *= 2; exponent--; } exponent++; assert (exponent >= FloatConsts.MIN_EXPONENT - (FloatConsts.SIGNIFICAND_WIDTH - 1) && exponent < FloatConsts.MIN_EXPONENT); return exponent; } // break; default: assert (exponent >= FloatConsts.MIN_EXPONENT && exponent <= FloatConsts.MAX_EXPONENT); return exponent; // break; } } /** * Returns unbiased exponent of a <code>double</code>. */ public static int getExponent(double d) { /* * Bitwise convert d to long, mask out exponent bits, shift * to the right and then subtract out double's bias adjust to * get true exponent value. */ return (int) (((Double.doubleToRawLongBits(d) & DoubleConsts.EXP_BIT_MASK) >> (DoubleConsts.SIGNIFICAND_WIDTH - 1)) - DoubleConsts.EXP_BIAS); } /** * Returns unbiased exponent of a <code>float</code>. */ public static int getExponent(float f) { /* * Bitwise convert f to integer, mask out exponent bits, shift * to the right and then subtract out float's bias adjust to * get true exponent value */ return ((Float.floatToRawIntBits(f) & FloatConsts.EXP_BIT_MASK) >> (FloatConsts.SIGNIFICAND_WIDTH - 1)) - FloatConsts.EXP_BIAS; } /** * Returns <code>true</code> if the specified number is a * Not-a-Number (NaN) value, <code>false</code> otherwise. * * <p>Note that this method is equivalent to the {@link * Double#isNaN(double) Double.isNaN} method; the functionality is * included in this class for convenience. * * @param d the value to be tested. * @return <code>true</code> if the value of the argument is NaN; * <code>false</code> otherwise. */ public static boolean isNaN(double d) { return Double.isNaN(d); } /** * Returns <code>true</code> if the specified number is a * Not-a-Number (NaN) value, <code>false</code> otherwise. * * <p>Note that this method is equivalent to the {@link * Float#isNaN(float) Float.isNaN} method; the functionality is * included in this class for convenience. * * @param f the value to be tested. * @return <code>true</code> if the argument is NaN; * <code>false</code> otherwise. */ public static boolean isNaN(float f) { return Float.isNaN(f); } }