src/java.base/share/classes/java/lang/Float.java

*** 29,38 ****
--- 29,39 ----
  import java.lang.constant.Constable;
  import java.lang.constant.ConstantDesc;
  import java.util.Optional;
  
  import jdk.internal.math.FloatingDecimal;
+ import jdk.internal.math.FloatToDecimal;
  import jdk.internal.HotSpotIntrinsicCandidate;
  
  /**
   * The {@code Float} class wraps a value of primitive type
   * {@code float} in an object. An object of type
*** 140,216 ****
       */
      @SuppressWarnings("unchecked")
      public static final Class<Float> TYPE = (Class<Float>) Class.getPrimitiveClass("float");
  
      /**
!      * Returns a string representation of the {@code float}
!      * argument. All characters mentioned below are ASCII characters.
       * <ul>
!      * <li>If the argument is NaN, the result is the string
!      * "{@code NaN}".
!      * <li>Otherwise, the result is a string that represents the sign and
!      *     magnitude (absolute value) of the argument. If the sign is
!      *     negative, the first character of the result is
!      *     '{@code -}' ({@code '\u005Cu002D'}); if the sign is
!      *     positive, no sign character appears in the result. As for
!      *     the magnitude <i>m</i>:
       * <ul>
!      * <li>If <i>m</i> is infinity, it is represented by the characters
!      *     {@code "Infinity"}; thus, positive infinity produces
!      *     the result {@code "Infinity"} and negative infinity
!      *     produces the result {@code "-Infinity"}.
!      * <li>If <i>m</i> is zero, it is represented by the characters
!      *     {@code "0.0"}; thus, negative zero produces the result
!      *     {@code "-0.0"} and positive zero produces the result
!      *     {@code "0.0"}.
!      * <li> If <i>m</i> is greater than or equal to 10<sup>-3</sup> but
!      *      less than 10<sup>7</sup>, then it is represented as the
!      *      integer part of <i>m</i>, in decimal form with no leading
!      *      zeroes, followed by '{@code .}'
!      *      ({@code '\u005Cu002E'}), followed by one or more
!      *      decimal digits representing the fractional part of
!      *      <i>m</i>.
!      * <li> If <i>m</i> is less than 10<sup>-3</sup> or greater than or
!      *      equal to 10<sup>7</sup>, then it is represented in
!      *      so-called "computerized scientific notation." Let <i>n</i>
!      *      be the unique integer such that 10<sup><i>n</i> </sup>&le;
!      *      <i>m</i> {@literal <} 10<sup><i>n</i>+1</sup>; then let <i>a</i>
!      *      be the mathematically exact quotient of <i>m</i> and
!      *      10<sup><i>n</i></sup> so that 1 &le; <i>a</i> {@literal <} 10.
!      *      The magnitude is then represented as the integer part of
!      *      <i>a</i>, as a single decimal digit, followed by
!      *      '{@code .}' ({@code '\u005Cu002E'}), followed by
!      *      decimal digits representing the fractional part of
!      *      <i>a</i>, followed by the letter '{@code E}'
!      *      ({@code '\u005Cu0045'}), followed by a representation
!      *      of <i>n</i> as a decimal integer, as produced by the
!      *      method {@link java.lang.Integer#toString(int)}.
!      *
       * </ul>
       * </ul>
-      * How many digits must be printed for the fractional part of
-      * <i>m</i> or <i>a</i>? There must be at least one digit
-      * to represent the fractional part, and beyond that as many, but
-      * only as many, more digits as are needed to uniquely distinguish
-      * the argument value from adjacent values of type
-      * {@code float}. That is, suppose that <i>x</i> is the
-      * exact mathematical value represented by the decimal
-      * representation produced by this method for a finite nonzero
-      * argument <i>f</i>. Then <i>f</i> must be the {@code float}
-      * value nearest to <i>x</i>; or, if two {@code float} values are
-      * equally close to <i>x</i>, then <i>f</i> must be one of
-      * them and the least significant bit of the significand of
-      * <i>f</i> must be {@code 0}.
       *
!      * <p>To create localized string representations of a floating-point
!      * value, use subclasses of {@link java.text.NumberFormat}.
       *
!      * @param   f   the float to be converted.
!      * @return a string representation of the argument.
       */
!     public static String toString(float f) {
!         return FloatingDecimal.toJavaFormatString(f);
      }
  
      /**
       * Returns a hexadecimal string representation of the
       * {@code float} argument. All characters mentioned below are
--- 141,264 ----
       */
      @SuppressWarnings("unchecked")
      public static final Class<Float> TYPE = (Class<Float>) Class.getPrimitiveClass("float");
  
      /**
!      * Returns a string rendering of the {@code float} argument.
!      *
!      * <p>The characters of the result are all drawn from the ASCII set.
       * <ul>
!      * <li> Any NaN, whether quiet or signaling, is rendered as
!      * {@code "NaN"}, regardless of the sign bit.
!      * <li> The infinities +&infin; and -&infin; are rendered as
!      * {@code "Infinity"} and {@code "-Infinity"}, respectively.
!      * <li> The positive and negative zeroes are rendered as
!      * {@code "0.0"} and {@code "-0.0"}, respectively.
!      * <li> A finite negative {@code v} is rendered as the sign
!      * '{@code -}' followed by the rendering of the magnitude -{@code v}.
!      * <li> A finite positive {@code v} is rendered in two stages:
       * <ul>
!      * <li> <em>Selection of a decimal</em>: A well-defined
!      * decimal <i>d</i><sub><code>v</code></sub> is selected
!      * to represent {@code v}.
!      * <li> <em>Formatting as a string</em>: The decimal
!      * <i>d</i><sub><code>v</code></sub> is formatted as a string,
!      * either in plain or in computerized scientific notation,
!      * depending on its value.
!      * </ul>
       * </ul>
+      *
+      * <p>A <em>decimal</em> is a number of the form
+      * <i>d</i>&times;10<sup><i>i</i></sup>
+      * for some (unique) integers <i>d</i> &gt; 0 and <i>i</i> such that
+      * <i>d</i> is not a multiple of 10.
+      * These integers are the <em>significand</em> and
+      * the <em>exponent</em>, respectively, of the decimal.
+      * The <em>length</em> of the decimal is the (unique)
+      * integer <i>n</i> meeting
+      * 10<sup><i>n</i>-1</sup> &le; <i>d</i> &lt; 10<sup><i>n</i></sup>.
+      *
+      * <p>The decimal <i>d</i><sub><code>v</code></sub>
+      * for a finite positive {@code v} is defined as follows:
+      * <ul>
+      * <li>Let <i>R</i> be the set of all decimals that round to {@code v}
+      * according to the usual round-to-closest rule of
+      * IEEE 754 floating-point arithmetic.
+      * <li>Let <i>m</i> be the minimal length over all decimals in <i>R</i>.
+      * <li>When <i>m</i> &ge; 2, let <i>T</i> be the set of all decimals
+      * in <i>R</i> with length <i>m</i>.
+      * Otherwise, let <i>T</i> be the set of all decimals
+      * in <i>R</i> with length 1 or 2.
+      * <li>Define <i>d</i><sub><code>v</code></sub> as
+      * the decimal in <i>T</i> that is closest to {@code v}.
+      * Or if there are two such decimals in <i>T</i>,
+      * select the one with the even significand (there is exactly one).
       * </ul>
       *
!      * <p>The (uniquely) selected decimal <i>d</i><sub><code>v</code></sub>
!      * is then formatted.
!      *
!      * <p>Let <i>d</i>, <i>i</i> and <i>n</i> be the significand, exponent and
!      * length of <i>d</i><sub><code>v</code></sub>, respectively.
!      * Further, let <i>e</i> = <i>n</i> + <i>i</i> - 1 and let
!      * <i>d</i><sub>1</sub>&hellip;<i>d</i><sub><i>n</i></sub>
!      * be the usual decimal expansion of the significand.
!      * Note that <i>d</i><sub>1</sub> &ne; 0 &ne; <i>d</i><sub><i>n</i></sub>.
!      * <ul>
!      * <li>Case -3 &le; <i>e</i> &lt; 0:
!      * <i>d</i><sub><code>v</code></sub> is formatted as
!      * <code>0.0</code>&hellip;<code>0</code><!--
!      * --><i>d</i><sub>1</sub>&hellip;<i>d</i><sub><i>n</i></sub>,
!      * where there are exactly -(<i>n</i> + <i>i</i>) zeroes between
!      * the decimal point and <i>d</i><sub>1</sub>.
!      * For example, 123 &times; 10<sup>-4</sup> is formatted as
!      * {@code 0.0123}.
!      * <li>Case 0 &le; <i>e</i> &lt; 7:
!      * <ul>
!      * <li>Subcase <i>i</i> &ge; 0:
!      * <i>d</i><sub><code>v</code></sub> is formatted as
!      * <i>d</i><sub>1</sub>&hellip;<i>d</i><sub><i>n</i></sub><!--
!      * --><code>0</code>&hellip;<code>0.0</code>,
!      * where there are exactly <i>i</i> zeroes
!      * between <i>d</i><sub><i>n</i></sub> and the decimal point.
!      * For example, 123 &times; 10<sup>2</sup> is formatted as
!      * {@code 12300.0}.
!      * <li>Subcase <i>i</i> &lt; 0:
!      * <i>d</i><sub><code>v</code></sub> is formatted as
!      * <i>d</i><sub>1</sub>&hellip;<!--
!      * --><i>d</i><sub><i>n</i>+<i>i</i></sub>.<!--
!      * --><i>d</i><sub><i>n</i>+<i>i</i>+1</sub>&hellip;<!--
!      * --><i>d</i><sub><i>n</i></sub>.
!      * There are exactly -<i>i</i> digits to the right of
!      * the decimal point.
!      * For example, 123 &times; 10<sup>-1</sup> is formatted as
!      * {@code 12.3}.
!      * </ul>
!      * <li>Case <i>e</i> &lt; -3 or <i>e</i> &ge; 7:
!      * computerized scientific notation is used to format
!      * <i>d</i><sub><code>v</code></sub>.
!      * Here <i>e</i> is formatted as by {@link Integer#toString(int)}.
!      * <ul>
!      * <li>Subcase <i>n</i> = 1:
!      * <i>d</i><sub><code>v</code></sub> is formatted as
!      * <i>d</i><sub>1</sub><code>.0E</code><i>e</i>.
!      * For example, 1 &times; 10<sup>23</sup> is formatted as
!      * {@code 1.0E23}.
!      * <li>Subcase <i>n</i> &gt; 1:
!      * <i>d</i><sub><code>v</code></sub> is formatted as
!      * <i>d</i><sub>1</sub><code>.</code><i>d</i><sub>2</sub><!--
!      * -->&hellip;<i>d</i><sub><i>n</i></sub><code>E</code><i>e</i>.
!      * For example, 123 &times; 10<sup>-21</sup> is formatted as
!      * {@code 1.23E-19}.
!      * </ul>
!      * </ul>
       *
!      * @param  v the {@code float} to be rendered.
!      * @return a string rendering of the argument.
       */
!     public static String toString(float v) {
!         return FloatToDecimal.toString(v);
      }
  
      /**
       * Returns a hexadecimal string representation of the
       * {@code float} argument. All characters mentioned below are