libjava/java/lang/Float.java

   1 /* Float.java -- object wrapper for float
   2    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.lang;
  40
  41 /**
  42  * Instances of class <code>Float</code> represent primitive
  43  * <code>float</code> values.
  44  *
  45  * Additionally, this class provides various helper functions and variables
  46  * related to floats.
  47  *
  48  * @author Paul Fisher
  49  * @author Andrew Haley <aph@cygnus.com>
  50  * @author Eric Blake <ebb9@email.byu.edu>
  51  * @since 1.0
  52  * @status updated to 1.4
  53  */
  54 public final class Float extends Number implements Comparable
  55 {
  56   /**
  57    * Compatible with JDK 1.0+.
  58    */
  59   private static final long serialVersionUID = -2671257302660747028L;
  60
  61   /**
  62    * The maximum positive value a <code>double</code> may represent
  63    * is 3.4028235e+38f.
  64    */
  65   public static final float MAX_VALUE = 3.4028235e+38f;
  66
  67   /**
  68    * The minimum positive value a <code>float</code> may represent
  69    * is 1.4e-45.
  70    */
  71   public static final float MIN_VALUE = 1.4e-45f;
  72
  73   /**
  74    * The value of a float representation -1.0/0.0, negative infinity.
  75    */
  76   public static final float NEGATIVE_INFINITY = -1.0f / 0.0f;
  77
  78   /**
  79    * The value of a float representation 1.0/0.0, positive infinity.
  80    */
  81   public static final float POSITIVE_INFINITY = 1.0f / 0.0f;
  82
  83   /**
  84    * All IEEE 754 values of NaN have the same value in Java.
  85    */
  86   public static final float NaN = 0.0f / 0.0f;
  87
  88   /**
  89    * The primitive type <code>float</code> is represented by this
  90    * <code>Class</code> object.
  91    * @since 1.1
  92    */
  93   public static final Class TYPE = VMClassLoader.getPrimitiveClass('F');
  94
  95   /**
  96    * The immutable value of this Float.
  97    *
  98    * @serial the wrapped float
  99    */
 100   private final float value;
 101
 102   /**
 103    * Create a <code>Float</code> from the primitive <code>float</code>
 104    * specified.
 105    *
 106    * @param value the <code>float</code> argument
 107    */
 108   public Float(float value)
 109   {
 110     this.value = value;
 111   }
 112
 113   /**
 114    * Create a <code>Float</code> from the primitive <code>double</code>
 115    * specified.
 116    *
 117    * @param value the <code>double</code> argument
 118    */
 119   public Float(double value)
 120   {
 121     this.value = (float) value;
 122   }
 123
 124   /**
 125    * Create a <code>Float</code> from the specified <code>String</code>.
 126    * This method calls <code>Float.parseFloat()</code>.
 127    *
 128    * @param s the <code>String</code> to convert
 129    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 130    *         <code>float</code>
 131    * @throws NullPointerException if <code>s</code> is null
 132    * @see #parseFloat(String)
 133    */
 134   public Float(String s)
 135   {
 136     value = parseFloat(s);
 137   }
 138
 139   /**
 140    * Convert the <code>float</code> to a <code>String</code>.
 141    * Floating-point string representation is fairly complex: here is a
 142    * rundown of the possible values.  "<code>[-]</code>" indicates that a
 143    * negative sign will be printed if the value (or exponent) is negative.
 144    * "<code>&lt;number&gt;</code>" means a string of digits ('0' to '9').
 145    * "<code>&lt;digit&gt;</code>" means a single digit ('0' to '9').<br>
 146    *
 147    * <table border=1>
 148    * <tr><th>Value of Float</th><th>String Representation</th></tr>
 149    * <tr><td>[+-] 0</td> <td><code>[-]0.0</code></td></tr>
 150    * <tr><td>Between [+-] 10<sup>-3</sup> and 10<sup>7</sup>, exclusive</td>
 151    *     <td><code>[-]number.number</code></td></tr>
 152    * <tr><td>Other numeric value</td>
 153    *     <td><code>[-]&lt;digit&gt;.&lt;number&gt;
 154    *          E[-]&lt;number&gt;</code></td></tr>
 155    * <tr><td>[+-] infinity</td> <td><code>[-]Infinity</code></td></tr>
 156    * <tr><td>NaN</td> <td><code>NaN</code></td></tr>
 157    * </table>
 158    *
 159    * Yes, negative zero <em>is</em> a possible value.  Note that there is
 160    * <em>always</em> a <code>.</code> and at least one digit printed after
 161    * it: even if the number is 3, it will be printed as <code>3.0</code>.
 162    * After the ".", all digits will be printed except trailing zeros. The
 163    * result is rounded to the shortest decimal number which will parse back
 164    * to the same float.
 165    *
 166    * <p>To create other output formats, use {@link java.text.NumberFormat}.
 167    *
 168    * @XXX specify where we are not in accord with the spec.
 169    *
 170    * @param f the <code>float</code> to convert
 171    * @return the <code>String</code> representing the <code>float</code>
 172    */
 173   public static String toString(float f)
 174   {
 175     return Double.toString(f, true);
 176   }
 177
 178   /**
 179    * Creates a new <code>Float</code> object using the <code>String</code>.
 180    *
 181    * @param s the <code>String</code> to convert
 182    * @return the new <code>Float</code>
 183    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 184    *         <code>float</code>
 185    * @throws NullPointerException if <code>s</code> is null
 186    * @see #parseFloat(String)
 187    */
 188   public static Float valueOf(String s)
 189   {
 190     return new Float(parseFloat(s));
 191   }
 192
 193   /**
 194    * Parse the specified <code>String</code> as a <code>float</code>. The
 195    * extended BNF grammar is as follows:<br>
 196    * <pre>
 197    * <em>DecodableString</em>:
 198    *      ( [ <code>-</code> | <code>+</code> ] <code>NaN</code> )
 199    *    | ( [ <code>-</code> | <code>+</code> ] <code>Infinity</code> )
 200    *    | ( [ <code>-</code> | <code>+</code> ] <em>FloatingPoint</em>
 201    *              [ <code>f</code> | <code>F</code> | <code>d</code>
 202    *                | <code>D</code>] )
 203    * <em>FloatingPoint</em>:
 204    *      ( { <em>Digit</em> }+ [ <code>.</code> { <em>Digit</em> } ]
 205    *              [ <em>Exponent</em> ] )
 206    *    | ( <code>.</code> { <em>Digit</em> }+ [ <em>Exponent</em> ] )
 207    * <em>Exponent</em>:
 208    *      ( ( <code>e</code> | <code>E</code> )
 209    *              [ <code>-</code> | <code>+</code> ] { <em>Digit</em> }+ )
 210    * <em>Digit</em>: <em><code>'0'</code> through <code>'9'</code></em>
 211    * </pre>
 212    *
 213    * <p>NaN and infinity are special cases, to allow parsing of the output
 214    * of toString.  Otherwise, the result is determined by calculating
 215    * <em>n * 10<sup>exponent</sup></em> to infinite precision, then rounding
 216    * to the nearest float. Remember that many numbers cannot be precisely
 217    * represented in floating point. In case of overflow, infinity is used,
 218    * and in case of underflow, signed zero is used. Unlike Integer.parseInt,
 219    * this does not accept Unicode digits outside the ASCII range.
 220    *
 221    * <p>If an unexpected character is found in the <code>String</code>, a
 222    * <code>NumberFormatException</code> will be thrown.  Leading and trailing
 223    * 'whitespace' is ignored via <code>String.trim()</code>, but spaces
 224    * internal to the actual number are not allowed.
 225    *
 226    * <p>To parse numbers according to another format, consider using
 227    * {@link java.text.NumberFormat}.
 228    *
 229    * @XXX specify where/how we are not in accord with the spec.
 230    *
 231    * @param str the <code>String</code> to convert
 232    * @return the <code>float</code> value of <code>s</code>
 233    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 234    *         <code>float</code>
 235    * @throws NullPointerException if <code>s</code> is null
 236    * @see #MIN_VALUE
 237    * @see #MAX_VALUE
 238    * @see #POSITIVE_INFINITY
 239    * @see #NEGATIVE_INFINITY
 240    * @since 1.2
 241    */
 242   public static float parseFloat(String s)
 243   {
 244     // XXX Rounding parseDouble() causes some errors greater than 1 ulp from
 245     // the infinitely precise decimal.
 246     return (float) Double.parseDouble(s);
 247   }
 248
 249   /**
 250    * Return <code>true</code> if the <code>float</code> has the same
 251    * value as <code>NaN</code>, otherwise return <code>false</code>.
 252    *
 253    * @param v the <code>float</code> to compare
 254    * @return whether the argument is <code>NaN</code>
 255    */
 256   public static boolean isNaN(float v)
 257   {
 258     // This works since NaN != NaN is the only reflexive inequality
 259     // comparison which returns true.
 260     return v != v;
 261   }
 262
 263   /**
 264    * Return <code>true</code> if the <code>float</code> has a value
 265    * equal to either <code>NEGATIVE_INFINITY</code> or
 266    * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
 267    *
 268    * @param v the <code>float</code> to compare
 269    * @return whether the argument is (-/+) infinity
 270    */
 271   public static boolean isInfinite(float v)
 272   {
 273     return v == POSITIVE_INFINITY || v == NEGATIVE_INFINITY;
 274   }
 275
 276   /**
 277    * Return <code>true</code> if the value of this <code>Float</code>
 278    * is the same as <code>NaN</code>, otherwise return <code>false</code>.
 279    *
 280    * @return whether this <code>Float</code> is <code>NaN</code>
 281    */
 282   public boolean isNaN()
 283   {
 284     return isNaN(value);
 285   }
 286
 287   /**
 288    * Return <code>true</code> if the value of this <code>Float</code>
 289    * is the same as <code>NEGATIVE_INFINITY</code> or
 290    * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
 291    *
 292    * @return whether this <code>Float</code> is (-/+) infinity
 293    */
 294   public boolean isInfinite()
 295   {
 296     return isInfinite(value);
 297   }
 298
 299   /**
 300    * Convert the <code>float</code> value of this <code>Float</code>
 301    * to a <code>String</code>.  This method calls
 302    * <code>Float.toString(float)</code> to do its dirty work.
 303    *
 304    * @return the <code>String</code> representation
 305    * @see #toString(float)
 306    */
 307   public String toString()
 308   {
 309     return toString(value);
 310   }
 311
 312   /**
 313    * Return the value of this <code>Float</code> as a <code>byte</code>.
 314    *
 315    * @return the byte value
 316    * @since 1.1
 317    */
 318   public byte byteValue()
 319   {
 320     return (byte) value;
 321   }
 322
 323   /**
 324    * Return the value of this <code>Float</code> as a <code>short</code>.
 325    *
 326    * @return the short value
 327    * @since 1.1
 328    */
 329   public short shortValue()
 330   {
 331     return (short) value;
 332   }
 333
 334   /**
 335    * Return the value of this <code>Integer</code> as an <code>int</code>.
 336    *
 337    * @return the int value
 338    */
 339   public int intValue()
 340   {
 341     return (int) value;
 342   }
 343
 344   /**
 345    * Return the value of this <code>Integer</code> as a <code>long</code>.
 346    *
 347    * @return the long value
 348    */
 349   public long longValue()
 350   {
 351     return (long) value;
 352   }
 353
 354   /**
 355    * Return the value of this <code>Float</code>.
 356    *
 357    * @return the float value
 358    */
 359   public float floatValue()
 360   {
 361     return value;
 362   }
 363
 364   /**
 365    * Return the value of this <code>Float</code> as a <code>double</code>
 366    *
 367    * @return the double value
 368    */
 369   public double doubleValue()
 370   {
 371     return value;
 372   }
 373
 374   /**
 375    * Return a hashcode representing this Object. <code>Float</code>'s hash
 376    * code is calculated by calling <code>floatToIntBits(floatValue())</code>.
 377    *
 378    * @return this Object's hash code
 379    * @see #floatToIntBits(float)
 380    */
 381   public int hashCode()
 382   {
 383     return floatToIntBits(value);
 384   }
 385
 386   /**
 387    * Returns <code>true</code> if <code>obj</code> is an instance of
 388    * <code>Float</code> and represents the same float value. Unlike comparing
 389    * two floats with <code>==</code>, this treats two instances of
 390    * <code>Float.NaN</code> as equal, but treats <code>0.0</code> and
 391    * <code>-0.0</code> as unequal.
 392    *
 393    * <p>Note that <code>f1.equals(f2)<code> is identical to
 394    * <code>floatToIntBits(f1.floatValue()) ==
 395    *    floatToIntBits(f2.floatValue())<code>.
 396    *
 397    * @param obj the object to compare
 398    * @return whether the objects are semantically equal
 399    */
 400   public boolean equals(Object obj)
 401   {
 402     if (! (obj instanceof Float))
 403       return false;
 404
 405     float f = ((Float) obj).value;
 406
 407     // Avoid call to native method. However, some implementations, like gcj,
 408     // are better off using floatToIntBits(value) == floatToIntBits(f).
 409     // Check common case first, then check NaN and 0.
 410     if (value == f)
 411       return (value != 0) || (1 / value == 1 / f);
 412     return isNaN(value) && isNaN(f);
 413   }
 414
 415   /**
 416    * Convert the float to the IEEE 754 floating-point "single format" bit
 417    * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
 418    * (masked by 0x7f800000) represent the exponent, and bits 22-0
 419    * (masked by 0x007fffff) are the mantissa. This function collapses all
 420    * versions of NaN to 0x7fc00000. The result of this function can be used
 421    * as the argument to <code>Float.intBitsToFloat(int)</code> to obtain the
 422    * original <code>float</code> value.
 423    *
 424    * @param value the <code>float</code> to convert
 425    * @return the bits of the <code>float</code>
 426    * @see #intBitsToFloat(int)
 427    */
 428   // GCJ LOCAL: We diverge from Classpath for efficiency.
 429   public static native int floatToIntBits(float value);
 430   // END GCJ LOCAL
 431
 432   /**
 433    * Convert the float to the IEEE 754 floating-point "single format" bit
 434    * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
 435    * (masked by 0x7f800000) represent the exponent, and bits 22-0
 436    * (masked by 0x007fffff) are the mantissa. This function leaves NaN alone,
 437    * rather than collapsing to a canonical value. The result of this function
 438    * can be used as the argument to <code>Float.intBitsToFloat(int)</code> to
 439    * obtain the original <code>float</code> value.
 440    *
 441    * @param value the <code>float</code> to convert
 442    * @return the bits of the <code>float</code>
 443    * @see #intBitsToFloat(int)
 444    */
 445   // GCJ LOCAL: We diverge from Classpath for efficiency.
 446   public static native int floatToRawIntBits(float value);
 447   // END GCJ LOCAL
 448
 449   /**
 450    * Convert the argument in IEEE 754 floating-point "single format" bit
 451    * layout to the corresponding float. Bit 31 (the most significant) is the
 452    * sign bit, bits 30-23 (masked by 0x7f800000) represent the exponent, and
 453    * bits 22-0 (masked by 0x007fffff) are the mantissa. This function leaves
 454    * NaN alone, so that you can recover the bit pattern with
 455    * <code>Float.floatToRawIntBits(float)</code>.
 456    *
 457    * @param bits the bits to convert
 458    * @return the <code>float</code> represented by the bits
 459    * @see #floatToIntBits(float)
 460    * @see #floatToRawIntBits(float)
 461    */
 462   // GCJ LOCAL: We diverge from Classpath for efficiency.
 463   public static native float intBitsToFloat(int bits);
 464   // END GCJ LOCAL
 465
 466   /**
 467    * Compare two Floats numerically by comparing their <code>float</code>
 468    * values. The result is positive if the first is greater, negative if the
 469    * second is greater, and 0 if the two are equal. However, this special
 470    * cases NaN and signed zero as follows: NaN is considered greater than
 471    * all other floats, including <code>POSITIVE_INFINITY</code>, and positive
 472    * zero is considered greater than negative zero.
 473    *
 474    * @param f the Float to compare
 475    * @return the comparison
 476    * @since 1.2
 477    */
 478   public int compareTo(Float f)
 479   {
 480     return compare(value, f.value);
 481   }
 482
 483   /**
 484    * Behaves like <code>compareTo(Float)</code> unless the Object
 485    * is not an <code>Float</code>.
 486    *
 487    * @param o the object to compare
 488    * @return the comparison
 489    * @throws ClassCastException if the argument is not a <code>Float</code>
 490    * @see #compareTo(Float)
 491    * @see Comparable
 492    * @since 1.2
 493    */
 494   public int compareTo(Object o)
 495   {
 496     return compare(value, ((Float) o).value);
 497   }
 498
 499   /**
 500    * Behaves like <code>new Float(x).compareTo(new Float(y))</code>; in
 501    * other words this compares two floats, special casing NaN and zero,
 502    * without the overhead of objects.
 503    *
 504    * @param x the first float to compare
 505    * @param y the second float to compare
 506    * @return the comparison
 507    * @since 1.4
 508    */
 509   public static int compare(float x, float y)
 510   {
 511     if (isNaN(x))
 512       return isNaN(y) ? 0 : 1;
 513     if (isNaN(y))
 514       return -1;
 515     // recall that 0.0 == -0.0, so we convert to infinities and try again
 516     if (x == 0 && y == 0)
 517       return (int) (1 / x - 1 / y);
 518     if (x == y)
 519       return 0;
 520
 521     return x > y ? 1 : -1;
 522   }
 523 }