001    /* Float.java -- object wrapper for float
002       Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
003       Free Software Foundation, Inc.
004    
005    This file is part of GNU Classpath.
006    
007    GNU Classpath is free software; you can redistribute it and/or modify
008    it under the terms of the GNU General Public License as published by
009    the Free Software Foundation; either version 2, or (at your option)
010    any later version.
011    
012    GNU Classpath is distributed in the hope that it will be useful, but
013    WITHOUT ANY WARRANTY; without even the implied warranty of
014    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015    General Public License for more details.
016    
017    You should have received a copy of the GNU General Public License
018    along with GNU Classpath; see the file COPYING.  If not, write to the
019    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
020    02110-1301 USA.
021    
022    Linking this library statically or dynamically with other modules is
023    making a combined work based on this library.  Thus, the terms and
024    conditions of the GNU General Public License cover the whole
025    combination.
026    
027    As a special exception, the copyright holders of this library give you
028    permission to link this library with independent modules to produce an
029    executable, regardless of the license terms of these independent
030    modules, and to copy and distribute the resulting executable under
031    terms of your choice, provided that you also meet, for each linked
032    independent module, the terms and conditions of the license of that
033    module.  An independent module is a module which is not derived from
034    or based on this library.  If you modify this library, you may extend
035    this exception to your version of the library, but you are not
036    obligated to do so.  If you do not wish to do so, delete this
037    exception statement from your version. */
038    
039    
040    package java.lang;
041    
042    /**
043     * Instances of class <code>Float</code> represent primitive
044     * <code>float</code> values.
045     *
046     * Additionally, this class provides various helper functions and variables
047     * related to floats.
048     *
049     * @author Paul Fisher
050     * @author Andrew Haley (aph@cygnus.com)
051     * @author Eric Blake (ebb9@email.byu.edu)
052     * @author Tom Tromey (tromey@redhat.com)
053     * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
054     * @since 1.0
055     * @status partly updated to 1.5
056     */
057    public final class Float extends Number implements Comparable<Float>
058    {
059      /**
060       * Compatible with JDK 1.0+.
061       */
062      private static final long serialVersionUID = -2671257302660747028L;
063    
064      /**
065       * The maximum positive value a <code>double</code> may represent
066       * is 3.4028235e+38f.
067       */
068      public static final float MAX_VALUE = 3.4028235e+38f;
069    
070      /**
071       * The minimum positive value a <code>float</code> may represent
072       * is 1.4e-45.
073       */
074      public static final float MIN_VALUE = 1.4e-45f;
075    
076      /**
077       * The value of a float representation -1.0/0.0, negative infinity.
078       */
079      public static final float NEGATIVE_INFINITY = -1.0f / 0.0f;
080    
081      /**
082       * The value of a float representation 1.0/0.0, positive infinity.
083       */
084      public static final float POSITIVE_INFINITY = 1.0f / 0.0f;
085    
086      /**
087       * All IEEE 754 values of NaN have the same value in Java.
088       */
089      public static final float NaN = 0.0f / 0.0f;
090    
091      /**
092       * The primitive type <code>float</code> is represented by this
093       * <code>Class</code> object.
094       * @since 1.1
095       */
096      public static final Class<Float> TYPE = (Class<Float>) VMClassLoader.getPrimitiveClass('F');
097    
098      /**
099       * The number of bits needed to represent a <code>float</code>.
100       * @since 1.5
101       */
102      public static final int SIZE = 32;
103    
104      /**
105       * The immutable value of this Float.
106       *
107       * @serial the wrapped float
108       */
109      private final float value;
110    
111      /**
112       * Create a <code>Float</code> from the primitive <code>float</code>
113       * specified.
114       *
115       * @param value the <code>float</code> argument
116       */
117      public Float(float value)
118      {
119        this.value = value;
120      }
121    
122      /**
123       * Create a <code>Float</code> from the primitive <code>double</code>
124       * specified.
125       *
126       * @param value the <code>double</code> argument
127       */
128      public Float(double value)
129      {
130        this.value = (float) value;
131      }
132    
133      /**
134       * Create a <code>Float</code> from the specified <code>String</code>.
135       * This method calls <code>Float.parseFloat()</code>.
136       *
137       * @param s the <code>String</code> to convert
138       * @throws NumberFormatException if <code>s</code> cannot be parsed as a
139       *         <code>float</code>
140       * @throws NullPointerException if <code>s</code> is null
141       * @see #parseFloat(String)
142       */
143      public Float(String s)
144      {
145        value = parseFloat(s);
146      }
147    
148      /**
149       * Convert the <code>float</code> to a <code>String</code>.
150       * Floating-point string representation is fairly complex: here is a
151       * rundown of the possible values.  "<code>[-]</code>" indicates that a
152       * negative sign will be printed if the value (or exponent) is negative.
153       * "<code>&lt;number&gt;</code>" means a string of digits ('0' to '9').
154       * "<code>&lt;digit&gt;</code>" means a single digit ('0' to '9').<br>
155       *
156       * <table border=1>
157       * <tr><th>Value of Float</th><th>String Representation</th></tr>
158       * <tr><td>[+-] 0</td> <td><code>[-]0.0</code></td></tr>
159       * <tr><td>Between [+-] 10<sup>-3</sup> and 10<sup>7</sup>, exclusive</td>
160       *     <td><code>[-]number.number</code></td></tr>
161       * <tr><td>Other numeric value</td>
162       *     <td><code>[-]&lt;digit&gt;.&lt;number&gt;
163       *          E[-]&lt;number&gt;</code></td></tr>
164       * <tr><td>[+-] infinity</td> <td><code>[-]Infinity</code></td></tr>
165       * <tr><td>NaN</td> <td><code>NaN</code></td></tr>
166       * </table>
167       *
168       * Yes, negative zero <em>is</em> a possible value.  Note that there is
169       * <em>always</em> a <code>.</code> and at least one digit printed after
170       * it: even if the number is 3, it will be printed as <code>3.0</code>.
171       * After the ".", all digits will be printed except trailing zeros. The
172       * result is rounded to the shortest decimal number which will parse back
173       * to the same float.
174       *
175       * <p>To create other output formats, use {@link java.text.NumberFormat}.
176       *
177       * @XXX specify where we are not in accord with the spec.
178       *
179       * @param f the <code>float</code> to convert
180       * @return the <code>String</code> representing the <code>float</code>
181       */
182      public static String toString(float f)
183      {
184        return VMFloat.toString(f);
185      }
186    
187      /**
188       * Convert a float value to a hexadecimal string.  This converts as
189       * follows:
190       * <ul>
191       * <li> A NaN value is converted to the string "NaN".
192       * <li> Positive infinity is converted to the string "Infinity".
193       * <li> Negative infinity is converted to the string "-Infinity".
194       * <li> For all other values, the first character of the result is '-'
195       * if the value is negative.  This is followed by '0x1.' if the
196       * value is normal, and '0x0.' if the value is denormal.  This is
197       * then followed by a (lower-case) hexadecimal representation of the
198       * mantissa, with leading zeros as required for denormal values.
199       * The next character is a 'p', and this is followed by a decimal
200       * representation of the unbiased exponent.
201       * </ul>
202       * @param f the float value
203       * @return the hexadecimal string representation
204       * @since 1.5
205       */
206      public static String toHexString(float f)
207      {
208        if (isNaN(f))
209          return "NaN";
210        if (isInfinite(f))
211          return f < 0 ? "-Infinity" : "Infinity";
212    
213        int bits = floatToIntBits(f);
214        StringBuilder result = new StringBuilder();
215        
216        if (bits < 0)
217          result.append('-');
218        result.append("0x");
219    
220        final int mantissaBits = 23;
221        final int exponentBits = 8;
222        int mantMask = (1 << mantissaBits) - 1;
223        int mantissa = bits & mantMask;
224        int expMask = (1 << exponentBits) - 1;
225        int exponent = (bits >>> mantissaBits) & expMask;
226    
227        result.append(exponent == 0 ? '0' : '1');
228        result.append('.');
229        // For Float only, we have to adjust the mantissa.
230        mantissa <<= 1;
231        result.append(Integer.toHexString(mantissa));
232        if (exponent == 0 && mantissa != 0)
233          {
234            // Treat denormal specially by inserting '0's to make
235            // the length come out right.  The constants here are
236            // to account for things like the '0x'.
237            int offset = 4 + ((bits < 0) ? 1 : 0);
238            // The silly +3 is here to keep the code the same between
239            // the Float and Double cases.  In Float the value is
240            // not a multiple of 4.
241            int desiredLength = offset + (mantissaBits + 3) / 4;
242            while (result.length() < desiredLength)
243              result.insert(offset, '0');
244          }
245        result.append('p');
246        if (exponent == 0 && mantissa == 0)
247          {
248            // Zero, so do nothing special.
249          }
250        else
251          {
252            // Apply bias.
253            boolean denormal = exponent == 0;
254            exponent -= (1 << (exponentBits - 1)) - 1;
255            // Handle denormal.
256            if (denormal)
257              ++exponent;
258          }
259    
260        result.append(Integer.toString(exponent));
261        return result.toString();
262      }
263    
264      /**
265       * Creates a new <code>Float</code> object using the <code>String</code>.
266       *
267       * @param s the <code>String</code> to convert
268       * @return the new <code>Float</code>
269       * @throws NumberFormatException if <code>s</code> cannot be parsed as a
270       *         <code>float</code>
271       * @throws NullPointerException if <code>s</code> is null
272       * @see #parseFloat(String)
273       */
274      public static Float valueOf(String s)
275      {
276        return new Float(parseFloat(s));
277      }
278    
279      /**
280       * Returns a <code>Float</code> object wrapping the value.
281       * In contrast to the <code>Float</code> constructor, this method
282       * may cache some values.  It is used by boxing conversion.
283       *
284       * @param val the value to wrap
285       * @return the <code>Float</code>
286       * @since 1.5
287       */
288      public static Float valueOf(float val)
289      {
290        // We don't actually cache, but we could.
291        return new Float(val);
292      }
293    
294      /**
295       * Parse the specified <code>String</code> as a <code>float</code>. The
296       * extended BNF grammar is as follows:<br>
297       * <pre>
298       * <em>DecodableString</em>:
299       *      ( [ <code>-</code> | <code>+</code> ] <code>NaN</code> )
300       *    | ( [ <code>-</code> | <code>+</code> ] <code>Infinity</code> )
301       *    | ( [ <code>-</code> | <code>+</code> ] <em>FloatingPoint</em>
302       *              [ <code>f</code> | <code>F</code> | <code>d</code>
303       *                | <code>D</code>] )
304       * <em>FloatingPoint</em>:
305       *      ( { <em>Digit</em> }+ [ <code>.</code> { <em>Digit</em> } ]
306       *              [ <em>Exponent</em> ] )
307       *    | ( <code>.</code> { <em>Digit</em> }+ [ <em>Exponent</em> ] )
308       * <em>Exponent</em>:
309       *      ( ( <code>e</code> | <code>E</code> )
310       *              [ <code>-</code> | <code>+</code> ] { <em>Digit</em> }+ )
311       * <em>Digit</em>: <em><code>'0'</code> through <code>'9'</code></em>
312       * </pre>
313       *
314       * <p>NaN and infinity are special cases, to allow parsing of the output
315       * of toString.  Otherwise, the result is determined by calculating
316       * <em>n * 10<sup>exponent</sup></em> to infinite precision, then rounding
317       * to the nearest float. Remember that many numbers cannot be precisely
318       * represented in floating point. In case of overflow, infinity is used,
319       * and in case of underflow, signed zero is used. Unlike Integer.parseInt,
320       * this does not accept Unicode digits outside the ASCII range.
321       *
322       * <p>If an unexpected character is found in the <code>String</code>, a
323       * <code>NumberFormatException</code> will be thrown.  Leading and trailing
324       * 'whitespace' is ignored via <code>String.trim()</code>, but spaces
325       * internal to the actual number are not allowed.
326       *
327       * <p>To parse numbers according to another format, consider using
328       * {@link java.text.NumberFormat}.
329       *
330       * @XXX specify where/how we are not in accord with the spec.
331       *
332       * @param str the <code>String</code> to convert
333       * @return the <code>float</code> value of <code>s</code>
334       * @throws NumberFormatException if <code>str</code> cannot be parsed as a
335       *         <code>float</code>
336       * @throws NullPointerException if <code>str</code> is null
337       * @see #MIN_VALUE
338       * @see #MAX_VALUE
339       * @see #POSITIVE_INFINITY
340       * @see #NEGATIVE_INFINITY
341       * @since 1.2
342       */
343      public static float parseFloat(String str)
344      {
345        return VMFloat.parseFloat(str);
346      }
347    
348      /**
349       * Return <code>true</code> if the <code>float</code> has the same
350       * value as <code>NaN</code>, otherwise return <code>false</code>.
351       *
352       * @param v the <code>float</code> to compare
353       * @return whether the argument is <code>NaN</code>
354       */
355      public static boolean isNaN(float v)
356      {
357        // This works since NaN != NaN is the only reflexive inequality
358        // comparison which returns true.
359        return v != v;
360      }
361    
362      /**
363       * Return <code>true</code> if the <code>float</code> has a value
364       * equal to either <code>NEGATIVE_INFINITY</code> or
365       * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
366       *
367       * @param v the <code>float</code> to compare
368       * @return whether the argument is (-/+) infinity
369       */
370      public static boolean isInfinite(float v)
371      {
372        return v == POSITIVE_INFINITY || v == NEGATIVE_INFINITY;
373      }
374    
375      /**
376       * Return <code>true</code> if the value of this <code>Float</code>
377       * is the same as <code>NaN</code>, otherwise return <code>false</code>.
378       *
379       * @return whether this <code>Float</code> is <code>NaN</code>
380       */
381      public boolean isNaN()
382      {
383        return isNaN(value);
384      }
385    
386      /**
387       * Return <code>true</code> if the value of this <code>Float</code>
388       * is the same as <code>NEGATIVE_INFINITY</code> or
389       * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
390       *
391       * @return whether this <code>Float</code> is (-/+) infinity
392       */
393      public boolean isInfinite()
394      {
395        return isInfinite(value);
396      }
397    
398      /**
399       * Convert the <code>float</code> value of this <code>Float</code>
400       * to a <code>String</code>.  This method calls
401       * <code>Float.toString(float)</code> to do its dirty work.
402       *
403       * @return the <code>String</code> representation
404       * @see #toString(float)
405       */
406      public String toString()
407      {
408        return toString(value);
409      }
410    
411      /**
412       * Return the value of this <code>Float</code> as a <code>byte</code>.
413       *
414       * @return the byte value
415       * @since 1.1
416       */
417      public byte byteValue()
418      {
419        return (byte) value;
420      }
421    
422      /**
423       * Return the value of this <code>Float</code> as a <code>short</code>.
424       *
425       * @return the short value
426       * @since 1.1
427       */
428      public short shortValue()
429      {
430        return (short) value;
431      }
432    
433      /**
434       * Return the value of this <code>Integer</code> as an <code>int</code>.
435       *
436       * @return the int value
437       */
438      public int intValue()
439      {
440        return (int) value;
441      }
442    
443      /**
444       * Return the value of this <code>Integer</code> as a <code>long</code>.
445       *
446       * @return the long value
447       */
448      public long longValue()
449      {
450        return (long) value;
451      }
452    
453      /**
454       * Return the value of this <code>Float</code>.
455       *
456       * @return the float value
457       */
458      public float floatValue()
459      {
460        return value;
461      }
462    
463      /**
464       * Return the value of this <code>Float</code> as a <code>double</code>
465       *
466       * @return the double value
467       */
468      public double doubleValue()
469      {
470        return value;
471      }
472    
473      /**
474       * Return a hashcode representing this Object. <code>Float</code>'s hash
475       * code is calculated by calling <code>floatToIntBits(floatValue())</code>.
476       *
477       * @return this Object's hash code
478       * @see #floatToIntBits(float)
479       */
480      public int hashCode()
481      {
482        return floatToIntBits(value);
483      }
484    
485      /**
486       * Returns <code>true</code> if <code>obj</code> is an instance of
487       * <code>Float</code> and represents the same float value. Unlike comparing
488       * two floats with <code>==</code>, this treats two instances of
489       * <code>Float.NaN</code> as equal, but treats <code>0.0</code> and
490       * <code>-0.0</code> as unequal.
491       *
492       * <p>Note that <code>f1.equals(f2)</code> is identical to
493       * <code>floatToIntBits(f1.floatValue()) ==
494       *    floatToIntBits(f2.floatValue())</code>.
495       *
496       * @param obj the object to compare
497       * @return whether the objects are semantically equal
498       */
499      public boolean equals(Object obj)
500      {
501        if (! (obj instanceof Float))
502          return false;
503    
504        float f = ((Float) obj).value;
505    
506        // Avoid call to native method. However, some implementations, like gcj,
507        // are better off using floatToIntBits(value) == floatToIntBits(f).
508        // Check common case first, then check NaN and 0.
509        if (value == f)
510          return (value != 0) || (1 / value == 1 / f);
511        return isNaN(value) && isNaN(f);
512      }
513    
514      /**
515       * Convert the float to the IEEE 754 floating-point "single format" bit
516       * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
517       * (masked by 0x7f800000) represent the exponent, and bits 22-0
518       * (masked by 0x007fffff) are the mantissa. This function collapses all
519       * versions of NaN to 0x7fc00000. The result of this function can be used
520       * as the argument to <code>Float.intBitsToFloat(int)</code> to obtain the
521       * original <code>float</code> value.
522       *
523       * @param value the <code>float</code> to convert
524       * @return the bits of the <code>float</code>
525       * @see #intBitsToFloat(int)
526       */
527      public static int floatToIntBits(float value)
528      {
529        return VMFloat.floatToIntBits(value);
530      }
531    
532      /**
533       * Convert the float to the IEEE 754 floating-point "single format" bit
534       * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
535       * (masked by 0x7f800000) represent the exponent, and bits 22-0
536       * (masked by 0x007fffff) are the mantissa. This function leaves NaN alone,
537       * rather than collapsing to a canonical value. The result of this function
538       * can be used as the argument to <code>Float.intBitsToFloat(int)</code> to
539       * obtain the original <code>float</code> value.
540       *
541       * @param value the <code>float</code> to convert
542       * @return the bits of the <code>float</code>
543       * @see #intBitsToFloat(int)
544       */
545      public static int floatToRawIntBits(float value)
546      {
547        return VMFloat.floatToRawIntBits(value);
548      }
549    
550      /**
551       * Convert the argument in IEEE 754 floating-point "single format" bit
552       * layout to the corresponding float. Bit 31 (the most significant) is the
553       * sign bit, bits 30-23 (masked by 0x7f800000) represent the exponent, and
554       * bits 22-0 (masked by 0x007fffff) are the mantissa. This function leaves
555       * NaN alone, so that you can recover the bit pattern with
556       * <code>Float.floatToRawIntBits(float)</code>.
557       *
558       * @param bits the bits to convert
559       * @return the <code>float</code> represented by the bits
560       * @see #floatToIntBits(float)
561       * @see #floatToRawIntBits(float)
562       */
563      public static float intBitsToFloat(int bits)
564      {
565        return VMFloat.intBitsToFloat(bits);
566      }
567    
568      /**
569       * Compare two Floats numerically by comparing their <code>float</code>
570       * values. The result is positive if the first is greater, negative if the
571       * second is greater, and 0 if the two are equal. However, this special
572       * cases NaN and signed zero as follows: NaN is considered greater than
573       * all other floats, including <code>POSITIVE_INFINITY</code>, and positive
574       * zero is considered greater than negative zero.
575       *
576       * @param f the Float to compare
577       * @return the comparison
578       * @since 1.2
579       */
580      public int compareTo(Float f)
581      {
582        return compare(value, f.value);
583      }
584    
585      /**
586       * Behaves like <code>new Float(x).compareTo(new Float(y))</code>; in
587       * other words this compares two floats, special casing NaN and zero,
588       * without the overhead of objects.
589       *
590       * @param x the first float to compare
591       * @param y the second float to compare
592       * @return the comparison
593       * @since 1.4
594       */
595      public static int compare(float x, float y)
596      {
597        if (isNaN(x))
598          return isNaN(y) ? 0 : 1;
599        if (isNaN(y))
600          return -1;
601        // recall that 0.0 == -0.0, so we convert to infinities and try again
602        if (x == 0 && y == 0)
603          return (int) (1 / x - 1 / y);
604        if (x == y)
605          return 0;
606    
607        return x > y ? 1 : -1;
608      }
609    }