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><number></code>" means a string of digits ('0' to '9'). 154 * "<code><digit></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>[-]<digit>.<number> 163 * E[-]<number></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 }