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    import gnu.java.lang.CPStringBuilder;
043    
044    /**
045     * Instances of class <code>Float</code> represent primitive
046     * <code>float</code> values.
047     *
048     * Additionally, this class provides various helper functions and variables
049     * related to floats.
050     *
051     * @author Paul Fisher
052     * @author Andrew Haley (aph@cygnus.com)
053     * @author Eric Blake (ebb9@email.byu.edu)
054     * @author Tom Tromey (tromey@redhat.com)
055     * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
056     * @since 1.0
057     * @status partly updated to 1.5
058     */
059    public final class Float extends Number implements Comparable<Float>
060    {
061      /**
062       * Compatible with JDK 1.0+.
063       */
064      private static final long serialVersionUID = -2671257302660747028L;
065    
066      /**
067       * The maximum positive value a <code>double</code> may represent
068       * is 3.4028235e+38f.
069       */
070      public static final float MAX_VALUE = 3.4028235e+38f;
071    
072      /**
073       * The minimum positive value a <code>float</code> may represent
074       * is 1.4e-45.
075       */
076      public static final float MIN_VALUE = 1.4e-45f;
077    
078      /**
079       * The value of a float representation -1.0/0.0, negative infinity.
080       */
081      public static final float NEGATIVE_INFINITY = -1.0f / 0.0f;
082    
083      /**
084       * The value of a float representation 1.0/0.0, positive infinity.
085       */
086      public static final float POSITIVE_INFINITY = 1.0f / 0.0f;
087    
088      /**
089       * All IEEE 754 values of NaN have the same value in Java.
090       */
091      public static final float NaN = 0.0f / 0.0f;
092    
093      /**
094       * The primitive type <code>float</code> is represented by this
095       * <code>Class</code> object.
096       * @since 1.1
097       */
098      public static final Class<Float> TYPE = (Class<Float>) VMClassLoader.getPrimitiveClass('F');
099    
100      /**
101       * The number of bits needed to represent a <code>float</code>.
102       * @since 1.5
103       */
104      public static final int SIZE = 32;
105    
106      /**
107       * Cache representation of 0
108       */
109      private static final Float ZERO = new Float(0.0f);
110    
111      /**
112       * Cache representation of 1
113       */
114      private static final Float ONE = new Float(1.0f);
115    
116      /**
117       * The immutable value of this Float.
118       *
119       * @serial the wrapped float
120       */
121      private final float value;
122    
123      /**
124       * Create a <code>Float</code> from the primitive <code>float</code>
125       * specified.
126       *
127       * @param value the <code>float</code> argument
128       */
129      public Float(float value)
130      {
131        this.value = value;
132      }
133    
134      /**
135       * Create a <code>Float</code> from the primitive <code>double</code>
136       * specified.
137       *
138       * @param value the <code>double</code> argument
139       */
140      public Float(double value)
141      {
142        this.value = (float) value;
143      }
144    
145      /**
146       * Create a <code>Float</code> from the specified <code>String</code>.
147       * This method calls <code>Float.parseFloat()</code>.
148       *
149       * @param s the <code>String</code> to convert
150       * @throws NumberFormatException if <code>s</code> cannot be parsed as a
151       *         <code>float</code>
152       * @throws NullPointerException if <code>s</code> is null
153       * @see #parseFloat(String)
154       */
155      public Float(String s)
156      {
157        value = parseFloat(s);
158      }
159    
160      /**
161       * Convert the <code>float</code> to a <code>String</code>.
162       * Floating-point string representation is fairly complex: here is a
163       * rundown of the possible values.  "<code>[-]</code>" indicates that a
164       * negative sign will be printed if the value (or exponent) is negative.
165       * "<code>&lt;number&gt;</code>" means a string of digits ('0' to '9').
166       * "<code>&lt;digit&gt;</code>" means a single digit ('0' to '9').<br>
167       *
168       * <table border=1>
169       * <tr><th>Value of Float</th><th>String Representation</th></tr>
170       * <tr><td>[+-] 0</td> <td><code>[-]0.0</code></td></tr>
171       * <tr><td>Between [+-] 10<sup>-3</sup> and 10<sup>7</sup>, exclusive</td>
172       *     <td><code>[-]number.number</code></td></tr>
173       * <tr><td>Other numeric value</td>
174       *     <td><code>[-]&lt;digit&gt;.&lt;number&gt;
175       *          E[-]&lt;number&gt;</code></td></tr>
176       * <tr><td>[+-] infinity</td> <td><code>[-]Infinity</code></td></tr>
177       * <tr><td>NaN</td> <td><code>NaN</code></td></tr>
178       * </table>
179       *
180       * Yes, negative zero <em>is</em> a possible value.  Note that there is
181       * <em>always</em> a <code>.</code> and at least one digit printed after
182       * it: even if the number is 3, it will be printed as <code>3.0</code>.
183       * After the ".", all digits will be printed except trailing zeros. The
184       * result is rounded to the shortest decimal number which will parse back
185       * to the same float.
186       *
187       * <p>To create other output formats, use {@link java.text.NumberFormat}.
188       *
189       * @XXX specify where we are not in accord with the spec.
190       *
191       * @param f the <code>float</code> to convert
192       * @return the <code>String</code> representing the <code>float</code>
193       */
194      public static String toString(float f)
195      {
196        return VMFloat.toString(f);
197      }
198    
199      /**
200       * Convert a float value to a hexadecimal string.  This converts as
201       * follows:
202       * <ul>
203       * <li> A NaN value is converted to the string "NaN".
204       * <li> Positive infinity is converted to the string "Infinity".
205       * <li> Negative infinity is converted to the string "-Infinity".
206       * <li> For all other values, the first character of the result is '-'
207       * if the value is negative.  This is followed by '0x1.' if the
208       * value is normal, and '0x0.' if the value is denormal.  This is
209       * then followed by a (lower-case) hexadecimal representation of the
210       * mantissa, with leading zeros as required for denormal values.
211       * The next character is a 'p', and this is followed by a decimal
212       * representation of the unbiased exponent.
213       * </ul>
214       * @param f the float value
215       * @return the hexadecimal string representation
216       * @since 1.5
217       */
218      public static String toHexString(float f)
219      {
220        if (isNaN(f))
221          return "NaN";
222        if (isInfinite(f))
223          return f < 0 ? "-Infinity" : "Infinity";
224    
225        int bits = floatToIntBits(f);
226        CPStringBuilder result = new CPStringBuilder();
227        
228        if (bits < 0)
229          result.append('-');
230        result.append("0x");
231    
232        final int mantissaBits = 23;
233        final int exponentBits = 8;
234        int mantMask = (1 << mantissaBits) - 1;
235        int mantissa = bits & mantMask;
236        int expMask = (1 << exponentBits) - 1;
237        int exponent = (bits >>> mantissaBits) & expMask;
238    
239        result.append(exponent == 0 ? '0' : '1');
240        result.append('.');
241        // For Float only, we have to adjust the mantissa.
242        mantissa <<= 1;
243        result.append(Integer.toHexString(mantissa));
244        if (exponent == 0 && mantissa != 0)
245          {
246            // Treat denormal specially by inserting '0's to make
247            // the length come out right.  The constants here are
248            // to account for things like the '0x'.
249            int offset = 4 + ((bits < 0) ? 1 : 0);
250            // The silly +3 is here to keep the code the same between
251            // the Float and Double cases.  In Float the value is
252            // not a multiple of 4.
253            int desiredLength = offset + (mantissaBits + 3) / 4;
254            while (result.length() < desiredLength)
255              result.insert(offset, '0');
256          }
257        result.append('p');
258        if (exponent == 0 && mantissa == 0)
259          {
260            // Zero, so do nothing special.
261          }
262        else
263          {
264            // Apply bias.
265            boolean denormal = exponent == 0;
266            exponent -= (1 << (exponentBits - 1)) - 1;
267            // Handle denormal.
268            if (denormal)
269              ++exponent;
270          }
271    
272        result.append(Integer.toString(exponent));
273        return result.toString();
274      }
275    
276      /**
277       * Creates a new <code>Float</code> object using the <code>String</code>.
278       *
279       * @param s the <code>String</code> to convert
280       * @return the new <code>Float</code>
281       * @throws NumberFormatException if <code>s</code> cannot be parsed as a
282       *         <code>float</code>
283       * @throws NullPointerException if <code>s</code> is null
284       * @see #parseFloat(String)
285       */
286      public static Float valueOf(String s)
287      {
288        return valueOf(parseFloat(s));
289      }
290    
291      /**
292       * Returns a <code>Float</code> object wrapping the value.
293       * In contrast to the <code>Float</code> constructor, this method
294       * may cache some values.  It is used by boxing conversion.
295       *
296       * @param val the value to wrap
297       * @return the <code>Float</code>
298       * @since 1.5
299       */
300      public static Float valueOf(float val)
301      {
302        if ((val == 0.0) && (floatToRawIntBits(val) == 0))
303          return ZERO;
304        else if (val == 1.0)
305          return ONE;
306        else
307          return new Float(val);
308      }
309    
310      /**
311       * Parse the specified <code>String</code> as a <code>float</code>. The
312       * extended BNF grammar is as follows:<br>
313       * <pre>
314       * <em>DecodableString</em>:
315       *      ( [ <code>-</code> | <code>+</code> ] <code>NaN</code> )
316       *    | ( [ <code>-</code> | <code>+</code> ] <code>Infinity</code> )
317       *    | ( [ <code>-</code> | <code>+</code> ] <em>FloatingPoint</em>
318       *              [ <code>f</code> | <code>F</code> | <code>d</code>
319       *                | <code>D</code>] )
320       * <em>FloatingPoint</em>:
321       *      ( { <em>Digit</em> }+ [ <code>.</code> { <em>Digit</em> } ]
322       *              [ <em>Exponent</em> ] )
323       *    | ( <code>.</code> { <em>Digit</em> }+ [ <em>Exponent</em> ] )
324       * <em>Exponent</em>:
325       *      ( ( <code>e</code> | <code>E</code> )
326       *              [ <code>-</code> | <code>+</code> ] { <em>Digit</em> }+ )
327       * <em>Digit</em>: <em><code>'0'</code> through <code>'9'</code></em>
328       * </pre>
329       *
330       * <p>NaN and infinity are special cases, to allow parsing of the output
331       * of toString.  Otherwise, the result is determined by calculating
332       * <em>n * 10<sup>exponent</sup></em> to infinite precision, then rounding
333       * to the nearest float. Remember that many numbers cannot be precisely
334       * represented in floating point. In case of overflow, infinity is used,
335       * and in case of underflow, signed zero is used. Unlike Integer.parseInt,
336       * this does not accept Unicode digits outside the ASCII range.
337       *
338       * <p>If an unexpected character is found in the <code>String</code>, a
339       * <code>NumberFormatException</code> will be thrown.  Leading and trailing
340       * 'whitespace' is ignored via <code>String.trim()</code>, but spaces
341       * internal to the actual number are not allowed.
342       *
343       * <p>To parse numbers according to another format, consider using
344       * {@link java.text.NumberFormat}.
345       *
346       * @XXX specify where/how we are not in accord with the spec.
347       *
348       * @param str the <code>String</code> to convert
349       * @return the <code>float</code> value of <code>s</code>
350       * @throws NumberFormatException if <code>str</code> cannot be parsed as a
351       *         <code>float</code>
352       * @throws NullPointerException if <code>str</code> is null
353       * @see #MIN_VALUE
354       * @see #MAX_VALUE
355       * @see #POSITIVE_INFINITY
356       * @see #NEGATIVE_INFINITY
357       * @since 1.2
358       */
359      public static float parseFloat(String str)
360      {
361        return VMFloat.parseFloat(str);
362      }
363    
364      /**
365       * Return <code>true</code> if the <code>float</code> has the same
366       * value as <code>NaN</code>, otherwise return <code>false</code>.
367       *
368       * @param v the <code>float</code> to compare
369       * @return whether the argument is <code>NaN</code>
370       */
371      public static boolean isNaN(float v)
372      {
373        // This works since NaN != NaN is the only reflexive inequality
374        // comparison which returns true.
375        return v != v;
376      }
377    
378      /**
379       * Return <code>true</code> if the <code>float</code> has a value
380       * equal to either <code>NEGATIVE_INFINITY</code> or
381       * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
382       *
383       * @param v the <code>float</code> to compare
384       * @return whether the argument is (-/+) infinity
385       */
386      public static boolean isInfinite(float v)
387      {
388        return v == POSITIVE_INFINITY || v == NEGATIVE_INFINITY;
389      }
390    
391      /**
392       * Return <code>true</code> if the value of this <code>Float</code>
393       * is the same as <code>NaN</code>, otherwise return <code>false</code>.
394       *
395       * @return whether this <code>Float</code> is <code>NaN</code>
396       */
397      public boolean isNaN()
398      {
399        return isNaN(value);
400      }
401    
402      /**
403       * Return <code>true</code> if the value of this <code>Float</code>
404       * is the same as <code>NEGATIVE_INFINITY</code> or
405       * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
406       *
407       * @return whether this <code>Float</code> is (-/+) infinity
408       */
409      public boolean isInfinite()
410      {
411        return isInfinite(value);
412      }
413    
414      /**
415       * Convert the <code>float</code> value of this <code>Float</code>
416       * to a <code>String</code>.  This method calls
417       * <code>Float.toString(float)</code> to do its dirty work.
418       *
419       * @return the <code>String</code> representation
420       * @see #toString(float)
421       */
422      public String toString()
423      {
424        return toString(value);
425      }
426    
427      /**
428       * Return the value of this <code>Float</code> as a <code>byte</code>.
429       *
430       * @return the byte value
431       * @since 1.1
432       */
433      public byte byteValue()
434      {
435        return (byte) value;
436      }
437    
438      /**
439       * Return the value of this <code>Float</code> as a <code>short</code>.
440       *
441       * @return the short value
442       * @since 1.1
443       */
444      public short shortValue()
445      {
446        return (short) value;
447      }
448    
449      /**
450       * Return the value of this <code>Integer</code> as an <code>int</code>.
451       *
452       * @return the int value
453       */
454      public int intValue()
455      {
456        return (int) value;
457      }
458    
459      /**
460       * Return the value of this <code>Integer</code> as a <code>long</code>.
461       *
462       * @return the long value
463       */
464      public long longValue()
465      {
466        return (long) value;
467      }
468    
469      /**
470       * Return the value of this <code>Float</code>.
471       *
472       * @return the float value
473       */
474      public float floatValue()
475      {
476        return value;
477      }
478    
479      /**
480       * Return the value of this <code>Float</code> as a <code>double</code>
481       *
482       * @return the double value
483       */
484      public double doubleValue()
485      {
486        return value;
487      }
488    
489      /**
490       * Return a hashcode representing this Object. <code>Float</code>'s hash
491       * code is calculated by calling <code>floatToIntBits(floatValue())</code>.
492       *
493       * @return this Object's hash code
494       * @see #floatToIntBits(float)
495       */
496      public int hashCode()
497      {
498        return floatToIntBits(value);
499      }
500    
501      /**
502       * Returns <code>true</code> if <code>obj</code> is an instance of
503       * <code>Float</code> and represents the same float value. Unlike comparing
504       * two floats with <code>==</code>, this treats two instances of
505       * <code>Float.NaN</code> as equal, but treats <code>0.0</code> and
506       * <code>-0.0</code> as unequal.
507       *
508       * <p>Note that <code>f1.equals(f2)</code> is identical to
509       * <code>floatToIntBits(f1.floatValue()) ==
510       *    floatToIntBits(f2.floatValue())</code>.
511       *
512       * @param obj the object to compare
513       * @return whether the objects are semantically equal
514       */
515      public boolean equals(Object obj)
516      {
517        if (obj instanceof Float)
518          {
519            float f = ((Float) obj).value;
520            return (floatToRawIntBits(value) == floatToRawIntBits(f)) ||
521              (isNaN(value) && isNaN(f));
522          }
523        return false;
524      }
525    
526      /**
527       * Convert the float to the IEEE 754 floating-point "single format" bit
528       * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
529       * (masked by 0x7f800000) represent the exponent, and bits 22-0
530       * (masked by 0x007fffff) are the mantissa. This function collapses all
531       * versions of NaN to 0x7fc00000. The result of this function can be used
532       * as the argument to <code>Float.intBitsToFloat(int)</code> to obtain the
533       * original <code>float</code> value.
534       *
535       * @param value the <code>float</code> to convert
536       * @return the bits of the <code>float</code>
537       * @see #intBitsToFloat(int)
538       */
539      public static int floatToIntBits(float value)
540      {
541        if (isNaN(value))
542          return 0x7fc00000;
543        else
544          return VMFloat.floatToRawIntBits(value);
545      }
546    
547      /**
548       * Convert the float to the IEEE 754 floating-point "single format" bit
549       * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
550       * (masked by 0x7f800000) represent the exponent, and bits 22-0
551       * (masked by 0x007fffff) are the mantissa. This function leaves NaN alone,
552       * rather than collapsing to a canonical value. The result of this function
553       * can be used as the argument to <code>Float.intBitsToFloat(int)</code> to
554       * obtain the original <code>float</code> value.
555       *
556       * @param value the <code>float</code> to convert
557       * @return the bits of the <code>float</code>
558       * @see #intBitsToFloat(int)
559       */
560      public static int floatToRawIntBits(float value)
561      {
562        return VMFloat.floatToRawIntBits(value);
563      }
564    
565      /**
566       * Convert the argument in IEEE 754 floating-point "single format" bit
567       * layout to the corresponding float. Bit 31 (the most significant) is the
568       * sign bit, bits 30-23 (masked by 0x7f800000) represent the exponent, and
569       * bits 22-0 (masked by 0x007fffff) are the mantissa. This function leaves
570       * NaN alone, so that you can recover the bit pattern with
571       * <code>Float.floatToRawIntBits(float)</code>.
572       *
573       * @param bits the bits to convert
574       * @return the <code>float</code> represented by the bits
575       * @see #floatToIntBits(float)
576       * @see #floatToRawIntBits(float)
577       */
578      public static float intBitsToFloat(int bits)
579      {
580        return VMFloat.intBitsToFloat(bits);
581      }
582    
583      /**
584       * Compare two Floats numerically by comparing their <code>float</code>
585       * values. The result is positive if the first is greater, negative if the
586       * second is greater, and 0 if the two are equal. However, this special
587       * cases NaN and signed zero as follows: NaN is considered greater than
588       * all other floats, including <code>POSITIVE_INFINITY</code>, and positive
589       * zero is considered greater than negative zero.
590       *
591       * @param f the Float to compare
592       * @return the comparison
593       * @since 1.2
594       */
595      public int compareTo(Float f)
596      {
597        return compare(value, f.value);
598      }
599    
600      /**
601       * Behaves like <code>new Float(x).compareTo(new Float(y))</code>; in
602       * other words this compares two floats, special casing NaN and zero,
603       * without the overhead of objects.
604       *
605       * @param x the first float to compare
606       * @param y the second float to compare
607       * @return the comparison
608       * @since 1.4
609       */
610      public static int compare(float x, float y)
611      {
612          // handle the easy cases:
613          if (x < y)
614              return -1;
615          if (x > y)
616              return 1;
617    
618          // handle equality respecting that 0.0 != -0.0 (hence not using x == y):
619          int ix = floatToRawIntBits(x);
620          int iy = floatToRawIntBits(y);
621          if (ix == iy)
622              return 0;
623    
624          // handle NaNs:
625          if (x != x)
626              return (y != y) ? 0 : 1;
627          else if (y != y)
628              return -1;
629    
630          // handle +/- 0.0
631          return (ix < iy) ? -1 : 1;
632      }
633    }