001/* Float.java -- object wrapper for float
002   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
003   Free Software Foundation, Inc.
004
005This file is part of GNU Classpath.
006
007GNU Classpath is free software; you can redistribute it and/or modify
008it under the terms of the GNU General Public License as published by
009the Free Software Foundation; either version 2, or (at your option)
010any later version.
011
012GNU Classpath is distributed in the hope that it will be useful, but
013WITHOUT ANY WARRANTY; without even the implied warranty of
014MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015General Public License for more details.
016
017You should have received a copy of the GNU General Public License
018along with GNU Classpath; see the file COPYING.  If not, write to the
019Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02002110-1301 USA.
021
022Linking this library statically or dynamically with other modules is
023making a combined work based on this library.  Thus, the terms and
024conditions of the GNU General Public License cover the whole
025combination.
026
027As a special exception, the copyright holders of this library give you
028permission to link this library with independent modules to produce an
029executable, regardless of the license terms of these independent
030modules, and to copy and distribute the resulting executable under
031terms of your choice, provided that you also meet, for each linked
032independent module, the terms and conditions of the license of that
033module.  An independent module is a module which is not derived from
034or based on this library.  If you modify this library, you may extend
035this exception to your version of the library, but you are not
036obligated to do so.  If you do not wish to do so, delete this
037exception statement from your version. */
038
039
040package java.lang;
041
042import 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 */
059public 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}