libjava/classpath/java/lang/Float.java

   1 /* Float.java -- object wrapper for float
   2    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2005
   3    Free Software Foundation, Inc.
   4
   5 This file is part of GNU Classpath.
   6
   7 GNU Classpath is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GNU Classpath is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU Classpath; see the file COPYING.  If not, write to the
  19 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  20 02110-1301 USA.
  21
  22 Linking this library statically or dynamically with other modules is
  23 making a combined work based on this library.  Thus, the terms and
  24 conditions of the GNU General Public License cover the whole
  25 combination.
  26
  27 As a special exception, the copyright holders of this library give you
  28 permission to link this library with independent modules to produce an
  29 executable, regardless of the license terms of these independent
  30 modules, and to copy and distribute the resulting executable under
  31 terms of your choice, provided that you also meet, for each linked
  32 independent module, the terms and conditions of the license of that
  33 module.  An independent module is a module which is not derived from
  34 or based on this library.  If you modify this library, you may extend
  35 this exception to your version of the library, but you are not
  36 obligated to do so.  If you do not wish to do so, delete this
  37 exception statement from your version. */
  38
  39
  40 package java.lang;
  41
  42 /**
  43  * Instances of class <code>Float</code> represent primitive
  44  * <code>float</code> values.
  45  *
  46  * Additionally, this class provides various helper functions and variables
  47  * related to floats.
  48  *
  49  * @author Paul Fisher
  50  * @author Andrew Haley (aph@cygnus.com)
  51  * @author Eric Blake (ebb9@email.byu.edu)
  52  * @since 1.0
  53  * @status updated to 1.4
  54  */
  55 public final class Float extends Number implements Comparable
  56 {
  57   /**
  58    * Compatible with JDK 1.0+.
  59    */
  60   private static final long serialVersionUID = -2671257302660747028L;
  61
  62   /**
  63    * The maximum positive value a <code>double</code> may represent
  64    * is 3.4028235e+38f.
  65    */
  66   public static final float MAX_VALUE = 3.4028235e+38f;
  67
  68   /**
  69    * The minimum positive value a <code>float</code> may represent
  70    * is 1.4e-45.
  71    */
  72   public static final float MIN_VALUE = 1.4e-45f;
  73
  74   /**
  75    * The value of a float representation -1.0/0.0, negative infinity.
  76    */
  77   public static final float NEGATIVE_INFINITY = -1.0f / 0.0f;
  78
  79   /**
  80    * The value of a float representation 1.0/0.0, positive infinity.
  81    */
  82   public static final float POSITIVE_INFINITY = 1.0f / 0.0f;
  83
  84   /**
  85    * All IEEE 754 values of NaN have the same value in Java.
  86    */
  87   public static final float NaN = 0.0f / 0.0f;
  88
  89   /**
  90    * The primitive type <code>float</code> is represented by this
  91    * <code>Class</code> object.
  92    * @since 1.1
  93    */
  94   public static final Class TYPE = VMClassLoader.getPrimitiveClass('F');
  95
  96   /**
  97    * The number of bits needed to represent a <code>float</code>.
  98    * @since 1.5
  99    */
 100   public static final int SIZE = 32;
 101
 102   /**
 103    * The immutable value of this Float.
 104    *
 105    * @serial the wrapped float
 106    */
 107   private final float value;
 108
 109   /**
 110    * Create a <code>Float</code> from the primitive <code>float</code>
 111    * specified.
 112    *
 113    * @param value the <code>float</code> argument
 114    */
 115   public Float(float value)
 116   {
 117     this.value = value;
 118   }
 119
 120   /**
 121    * Create a <code>Float</code> from the primitive <code>double</code>
 122    * specified.
 123    *
 124    * @param value the <code>double</code> argument
 125    */
 126   public Float(double value)
 127   {
 128     this.value = (float) value;
 129   }
 130
 131   /**
 132    * Create a <code>Float</code> from the specified <code>String</code>.
 133    * This method calls <code>Float.parseFloat()</code>.
 134    *
 135    * @param s the <code>String</code> to convert
 136    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 137    *         <code>float</code>
 138    * @throws NullPointerException if <code>s</code> is null
 139    * @see #parseFloat(String)
 140    */
 141   public Float(String s)
 142   {
 143     value = parseFloat(s);
 144   }
 145
 146   /**
 147    * Convert the <code>float</code> to a <code>String</code>.
 148    * Floating-point string representation is fairly complex: here is a
 149    * rundown of the possible values.  "<code>[-]</code>" indicates that a
 150    * negative sign will be printed if the value (or exponent) is negative.
 151    * "<code>&lt;number&gt;</code>" means a string of digits ('0' to '9').
 152    * "<code>&lt;digit&gt;</code>" means a single digit ('0' to '9').<br>
 153    *
 154    * <table border=1>
 155    * <tr><th>Value of Float</th><th>String Representation</th></tr>
 156    * <tr><td>[+-] 0</td> <td><code>[-]0.0</code></td></tr>
 157    * <tr><td>Between [+-] 10<sup>-3</sup> and 10<sup>7</sup>, exclusive</td>
 158    *     <td><code>[-]number.number</code></td></tr>
 159    * <tr><td>Other numeric value</td>
 160    *     <td><code>[-]&lt;digit&gt;.&lt;number&gt;
 161    *          E[-]&lt;number&gt;</code></td></tr>
 162    * <tr><td>[+-] infinity</td> <td><code>[-]Infinity</code></td></tr>
 163    * <tr><td>NaN</td> <td><code>NaN</code></td></tr>
 164    * </table>
 165    *
 166    * Yes, negative zero <em>is</em> a possible value.  Note that there is
 167    * <em>always</em> a <code>.</code> and at least one digit printed after
 168    * it: even if the number is 3, it will be printed as <code>3.0</code>.
 169    * After the ".", all digits will be printed except trailing zeros. The
 170    * result is rounded to the shortest decimal number which will parse back
 171    * to the same float.
 172    *
 173    * <p>To create other output formats, use {@link java.text.NumberFormat}.
 174    *
 175    * @XXX specify where we are not in accord with the spec.
 176    *
 177    * @param f the <code>float</code> to convert
 178    * @return the <code>String</code> representing the <code>float</code>
 179    */
 180   public static String toString(float f)
 181   {
 182     return VMDouble.toString(f, true);
 183   }
 184
 185   /**
 186    * Convert a float value to a hexadecimal string.  This converts as
 187    * follows:
 188    * <ul>
 189    * <li> A NaN value is converted to the string "NaN".
 190    * <li> Positive infinity is converted to the string "Infinity".
 191    * <li> Negative infinity is converted to the string "-Infinity".
 192    * <li> For all other values, the first character of the result is '-'
 193    * if the value is negative.  This is followed by '0x1.' if the
 194    * value is normal, and '0x0.' if the value is denormal.  This is
 195    * then followed by a (lower-case) hexadecimal representation of the
 196    * mantissa, with leading zeros as required for denormal values.
 197    * The next character is a 'p', and this is followed by a decimal
 198    * representation of the unbiased exponent.
 199    * </ul>
 200    * @param f the float value
 201    * @return the hexadecimal string representation
 202    * @since 1.5
 203    */
 204   public static String toHexString(float f)
 205   {
 206     if (isNaN(f))
 207       return "NaN";
 208     if (isInfinite(f))
 209       return f < 0 ? "-Infinity" : "Infinity";
 210
 211     int bits = floatToIntBits(f);
 212     StringBuilder result = new StringBuilder();
 213
 214     if (bits < 0)
 215       result.append('-');
 216     result.append("0x");
 217
 218     final int mantissaBits = 23;
 219     final int exponentBits = 8;
 220     int mantMask = (1 << mantissaBits) - 1;
 221     int mantissa = bits & mantMask;
 222     int expMask = (1 << exponentBits) - 1;
 223     int exponent = (bits >>> mantissaBits) & expMask;
 224
 225     result.append(exponent == 0 ? '0' : '1');
 226     result.append('.');
 227     // For Float only, we have to adjust the mantissa.
 228     mantissa <<= 1;
 229     result.append(Integer.toHexString(mantissa));
 230     if (exponent == 0 && mantissa != 0)
 231       {
 232         // Treat denormal specially by inserting '0's to make
 233         // the length come out right.  The constants here are
 234         // to account for things like the '0x'.
 235         int offset = 4 + ((bits < 0) ? 1 : 0);
 236         // The silly +3 is here to keep the code the same between
 237         // the Float and Double cases.  In Float the value is
 238         // not a multiple of 4.
 239         int desiredLength = offset + (mantissaBits + 3) / 4;
 240         while (result.length() < desiredLength)
 241           result.insert(offset, '0');
 242       }
 243     result.append('p');
 244     if (exponent == 0 && mantissa == 0)
 245       {
 246         // Zero, so do nothing special.
 247       }
 248     else
 249       {
 250         // Apply bias.
 251         boolean denormal = exponent == 0;
 252         exponent -= (1 << (exponentBits - 1)) - 1;
 253         // Handle denormal.
 254         if (denormal)
 255           ++exponent;
 256       }
 257
 258     result.append(Integer.toString(exponent));
 259     return result.toString();
 260   }
 261
 262   /**
 263    * Creates a new <code>Float</code> object using the <code>String</code>.
 264    *
 265    * @param s the <code>String</code> to convert
 266    * @return the new <code>Float</code>
 267    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 268    *         <code>float</code>
 269    * @throws NullPointerException if <code>s</code> is null
 270    * @see #parseFloat(String)
 271    */
 272   public static Float valueOf(String s)
 273   {
 274     return new Float(parseFloat(s));
 275   }
 276
 277   /**
 278    * Returns a <code>Float</code> object wrapping the value.
 279    * In contrast to the <code>Float</code> constructor, this method
 280    * may cache some values.  It is used by boxing conversion.
 281    *
 282    * @param val the value to wrap
 283    * @return the <code>Float</code>
 284    *
 285    * @since 1.5
 286    */
 287   public static Float valueOf(float val)
 288   {
 289     // We don't actually cache, but we could.
 290     return new Float(val);
 291   }
 292
 293   /**
 294    * Parse the specified <code>String</code> as a <code>float</code>. The
 295    * extended BNF grammar is as follows:<br>
 296    * <pre>
 297    * <em>DecodableString</em>:
 298    *      ( [ <code>-</code> | <code>+</code> ] <code>NaN</code> )
 299    *    | ( [ <code>-</code> | <code>+</code> ] <code>Infinity</code> )
 300    *    | ( [ <code>-</code> | <code>+</code> ] <em>FloatingPoint</em>
 301    *              [ <code>f</code> | <code>F</code> | <code>d</code>
 302    *                | <code>D</code>] )
 303    * <em>FloatingPoint</em>:
 304    *      ( { <em>Digit</em> }+ [ <code>.</code> { <em>Digit</em> } ]
 305    *              [ <em>Exponent</em> ] )
 306    *    | ( <code>.</code> { <em>Digit</em> }+ [ <em>Exponent</em> ] )
 307    * <em>Exponent</em>:
 308    *      ( ( <code>e</code> | <code>E</code> )
 309    *              [ <code>-</code> | <code>+</code> ] { <em>Digit</em> }+ )
 310    * <em>Digit</em>: <em><code>'0'</code> through <code>'9'</code></em>
 311    * </pre>
 312    *
 313    * <p>NaN and infinity are special cases, to allow parsing of the output
 314    * of toString.  Otherwise, the result is determined by calculating
 315    * <em>n * 10<sup>exponent</sup></em> to infinite precision, then rounding
 316    * to the nearest float. Remember that many numbers cannot be precisely
 317    * represented in floating point. In case of overflow, infinity is used,
 318    * and in case of underflow, signed zero is used. Unlike Integer.parseInt,
 319    * this does not accept Unicode digits outside the ASCII range.
 320    *
 321    * <p>If an unexpected character is found in the <code>String</code>, a
 322    * <code>NumberFormatException</code> will be thrown.  Leading and trailing
 323    * 'whitespace' is ignored via <code>String.trim()</code>, but spaces
 324    * internal to the actual number are not allowed.
 325    *
 326    * <p>To parse numbers according to another format, consider using
 327    * {@link java.text.NumberFormat}.
 328    *
 329    * @XXX specify where/how we are not in accord with the spec.
 330    *
 331    * @param str the <code>String</code> to convert
 332    * @return the <code>float</code> value of <code>s</code>
 333    * @throws NumberFormatException if <code>s</code> cannot be parsed as a
 334    *         <code>float</code>
 335    * @throws NullPointerException if <code>s</code> is null
 336    * @see #MIN_VALUE
 337    * @see #MAX_VALUE
 338    * @see #POSITIVE_INFINITY
 339    * @see #NEGATIVE_INFINITY
 340    * @since 1.2
 341    */
 342   public static float parseFloat(String str)
 343   {
 344     // XXX Rounding parseDouble() causes some errors greater than 1 ulp from
 345     // the infinitely precise decimal.
 346     return (float) Double.parseDouble(str);
 347   }
 348
 349   /**
 350    * Return <code>true</code> if the <code>float</code> has the same
 351    * value as <code>NaN</code>, otherwise return <code>false</code>.
 352    *
 353    * @param v the <code>float</code> to compare
 354    * @return whether the argument is <code>NaN</code>
 355    */
 356   public static boolean isNaN(float v)
 357   {
 358     // This works since NaN != NaN is the only reflexive inequality
 359     // comparison which returns true.
 360     return v != v;
 361   }
 362
 363   /**
 364    * Return <code>true</code> if the <code>float</code> has a value
 365    * equal to either <code>NEGATIVE_INFINITY</code> or
 366    * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
 367    *
 368    * @param v the <code>float</code> to compare
 369    * @return whether the argument is (-/+) infinity
 370    */
 371   public static boolean isInfinite(float v)
 372   {
 373     return v == POSITIVE_INFINITY || v == NEGATIVE_INFINITY;
 374   }
 375
 376   /**
 377    * Return <code>true</code> if the value of this <code>Float</code>
 378    * is the same as <code>NaN</code>, otherwise return <code>false</code>.
 379    *
 380    * @return whether this <code>Float</code> is <code>NaN</code>
 381    */
 382   public boolean isNaN()
 383   {
 384     return isNaN(value);
 385   }
 386
 387   /**
 388    * Return <code>true</code> if the value of this <code>Float</code>
 389    * is the same as <code>NEGATIVE_INFINITY</code> or
 390    * <code>POSITIVE_INFINITY</code>, otherwise return <code>false</code>.
 391    *
 392    * @return whether this <code>Float</code> is (-/+) infinity
 393    */
 394   public boolean isInfinite()
 395   {
 396     return isInfinite(value);
 397   }
 398
 399   /**
 400    * Convert the <code>float</code> value of this <code>Float</code>
 401    * to a <code>String</code>.  This method calls
 402    * <code>Float.toString(float)</code> to do its dirty work.
 403    *
 404    * @return the <code>String</code> representation
 405    * @see #toString(float)
 406    */
 407   public String toString()
 408   {
 409     return toString(value);
 410   }
 411
 412   /**
 413    * Return the value of this <code>Float</code> as a <code>byte</code>.
 414    *
 415    * @return the byte value
 416    * @since 1.1
 417    */
 418   public byte byteValue()
 419   {
 420     return (byte) value;
 421   }
 422
 423   /**
 424    * Return the value of this <code>Float</code> as a <code>short</code>.
 425    *
 426    * @return the short value
 427    * @since 1.1
 428    */
 429   public short shortValue()
 430   {
 431     return (short) value;
 432   }
 433
 434   /**
 435    * Return the value of this <code>Integer</code> as an <code>int</code>.
 436    *
 437    * @return the int value
 438    */
 439   public int intValue()
 440   {
 441     return (int) value;
 442   }
 443
 444   /**
 445    * Return the value of this <code>Integer</code> as a <code>long</code>.
 446    *
 447    * @return the long value
 448    */
 449   public long longValue()
 450   {
 451     return (long) value;
 452   }
 453
 454   /**
 455    * Return the value of this <code>Float</code>.
 456    *
 457    * @return the float value
 458    */
 459   public float floatValue()
 460   {
 461     return value;
 462   }
 463
 464   /**
 465    * Return the value of this <code>Float</code> as a <code>double</code>
 466    *
 467    * @return the double value
 468    */
 469   public double doubleValue()
 470   {
 471     return value;
 472   }
 473
 474   /**
 475    * Return a hashcode representing this Object. <code>Float</code>'s hash
 476    * code is calculated by calling <code>floatToIntBits(floatValue())</code>.
 477    *
 478    * @return this Object's hash code
 479    * @see #floatToIntBits(float)
 480    */
 481   public int hashCode()
 482   {
 483     return floatToIntBits(value);
 484   }
 485
 486   /**
 487    * Returns <code>true</code> if <code>obj</code> is an instance of
 488    * <code>Float</code> and represents the same float value. Unlike comparing
 489    * two floats with <code>==</code>, this treats two instances of
 490    * <code>Float.NaN</code> as equal, but treats <code>0.0</code> and
 491    * <code>-0.0</code> as unequal.
 492    *
 493    * <p>Note that <code>f1.equals(f2)</code> is identical to
 494    * <code>floatToIntBits(f1.floatValue()) ==
 495    *    floatToIntBits(f2.floatValue())</code>.
 496    *
 497    * @param obj the object to compare
 498    * @return whether the objects are semantically equal
 499    */
 500   public boolean equals(Object obj)
 501   {
 502     if (! (obj instanceof Float))
 503       return false;
 504
 505     float f = ((Float) obj).value;
 506
 507     // Avoid call to native method. However, some implementations, like gcj,
 508     // are better off using floatToIntBits(value) == floatToIntBits(f).
 509     // Check common case first, then check NaN and 0.
 510     if (value == f)
 511       return (value != 0) || (1 / value == 1 / f);
 512     return isNaN(value) && isNaN(f);
 513   }
 514
 515   /**
 516    * Convert the float to the IEEE 754 floating-point "single format" bit
 517    * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
 518    * (masked by 0x7f800000) represent the exponent, and bits 22-0
 519    * (masked by 0x007fffff) are the mantissa. This function collapses all
 520    * versions of NaN to 0x7fc00000. The result of this function can be used
 521    * as the argument to <code>Float.intBitsToFloat(int)</code> to obtain the
 522    * original <code>float</code> value.
 523    *
 524    * @param value the <code>float</code> to convert
 525    * @return the bits of the <code>float</code>
 526    * @see #intBitsToFloat(int)
 527    */
 528   public static int floatToIntBits(float value)
 529   {
 530     return VMFloat.floatToIntBits(value);
 531   }
 532
 533   /**
 534    * Convert the float to the IEEE 754 floating-point "single format" bit
 535    * layout. Bit 31 (the most significant) is the sign bit, bits 30-23
 536    * (masked by 0x7f800000) represent the exponent, and bits 22-0
 537    * (masked by 0x007fffff) are the mantissa. This function leaves NaN alone,
 538    * rather than collapsing to a canonical value. The result of this function
 539    * can be used as the argument to <code>Float.intBitsToFloat(int)</code> to
 540    * obtain the original <code>float</code> value.
 541    *
 542    * @param value the <code>float</code> to convert
 543    * @return the bits of the <code>float</code>
 544    * @see #intBitsToFloat(int)
 545    */
 546   public static int floatToRawIntBits(float value)
 547   {
 548     return VMFloat.floatToRawIntBits(value);
 549   }
 550
 551   /**
 552    * Convert the argument in IEEE 754 floating-point "single format" bit
 553    * layout to the corresponding float. Bit 31 (the most significant) is the
 554    * sign bit, bits 30-23 (masked by 0x7f800000) represent the exponent, and
 555    * bits 22-0 (masked by 0x007fffff) are the mantissa. This function leaves
 556    * NaN alone, so that you can recover the bit pattern with
 557    * <code>Float.floatToRawIntBits(float)</code>.
 558    *
 559    * @param bits the bits to convert
 560    * @return the <code>float</code> represented by the bits
 561    * @see #floatToIntBits(float)
 562    * @see #floatToRawIntBits(float)
 563    */
 564   public static float intBitsToFloat(int bits)
 565   {
 566     return VMFloat.intBitsToFloat(bits);
 567   }
 568
 569   /**
 570    * Compare two Floats numerically by comparing their <code>float</code>
 571    * values. The result is positive if the first is greater, negative if the
 572    * second is greater, and 0 if the two are equal. However, this special
 573    * cases NaN and signed zero as follows: NaN is considered greater than
 574    * all other floats, including <code>POSITIVE_INFINITY</code>, and positive
 575    * zero is considered greater than negative zero.
 576    *
 577    * @param f the Float to compare
 578    * @return the comparison
 579    * @since 1.2
 580    */
 581   public int compareTo(Float f)
 582   {
 583     return compare(value, f.value);
 584   }
 585
 586   /**
 587    * Behaves like <code>compareTo(Float)</code> unless the Object
 588    * is not an <code>Float</code>.
 589    *
 590    * @param o the object to compare
 591    * @return the comparison
 592    * @throws ClassCastException if the argument is not a <code>Float</code>
 593    * @see #compareTo(Float)
 594    * @see Comparable
 595    * @since 1.2
 596    */
 597   public int compareTo(Object o)
 598   {
 599     return compare(value, ((Float) o).value);
 600   }
 601
 602   /**
 603    * Behaves like <code>new Float(x).compareTo(new Float(y))</code>; in
 604    * other words this compares two floats, special casing NaN and zero,
 605    * without the overhead of objects.
 606    *
 607    * @param x the first float to compare
 608    * @param y the second float to compare
 609    * @return the comparison
 610    * @since 1.4
 611    */
 612   public static int compare(float x, float y)
 613   {
 614     if (isNaN(x))
 615       return isNaN(y) ? 0 : 1;
 616     if (isNaN(y))
 617       return -1;
 618     // recall that 0.0 == -0.0, so we convert to infinities and try again
 619     if (x == 0 && y == 0)
 620       return (int) (1 / x - 1 / y);
 621     if (x == y)
 622       return 0;
 623
 624     return x > y ? 1 : -1;
 625   }
 626 }