8300869: Make use of the Double.toString(double) algorithm in java.util.Formatter

src/java.base/share/classes/java/util/Formatter.java

@@ -61,7 +61,7 @@
 import java.time.temporal.UnsupportedTemporalTypeException;
 
 import jdk.internal.math.DoubleConsts;
-import jdk.internal.math.FormattedFloatingDecimal;
+import jdk.internal.math.FormattedFPDecimal;
 import sun.util.locale.provider.LocaleProviderAdapter;
 import sun.util.locale.provider.ResourceBundleBasedAdapter;
 
@@ -1260,6 +1260,9 @@
  *     id="scientific">computerized scientific notation</a>.  The <a
  *     href="#L10nAlgorithm">localization algorithm</a> is applied.
  *
+ *     <p> A {@code float} or {@link Float} argument is first converted to
+ *     {@code double} or {@link Double}, without loss of precision.
+ *
  *     <p> The formatting of the magnitude <i>m</i> depends upon its value.
  *
  *     <p> If <i>m</i> is NaN or infinite, the literal strings "NaN" or
@@ -1291,8 +1294,8 @@
  *     <i>m</i> or <i>a</i> is equal to the precision.  If the precision is not
  *     specified then the default value is {@code 6}. If the precision is less
  *     than the number of digits which would appear after the decimal point in
- *     the string returned by {@link Float#toString(float)} or {@link
- *     Double#toString(double)} respectively, then the value will be rounded
+ *     the string returned by {@link
+ *     Double#toString(double)}, then the value will be rounded
  *     using the {@linkplain java.math.RoundingMode#HALF_UP round half up
  *     algorithm}.  Otherwise, zeros may be appended to reach the precision.
  *     For a canonical representation of the value, use {@link
@@ -1342,6 +1345,9 @@
  *     format</a>.  The <a href="#L10nAlgorithm">localization algorithm</a> is
  *     applied.
  *
+ *     <p> A {@code float} or {@link Float} argument is first converted to
+ *     {@code double} or {@link Double}, without loss of precision.
+ *
  *     <p> The result is a string that represents the sign and magnitude
  *     (absolute value) of the argument.  The formatting of the sign is
  *     described in the <a href="#L10nAlgorithm">localization
@@ -1360,8 +1366,8 @@
  *     <i>m</i> or <i>a</i> is equal to the precision.  If the precision is not
  *     specified then the default value is {@code 6}. If the precision is less
  *     than the number of digits which would appear after the decimal point in
- *     the string returned by {@link Float#toString(float)} or {@link
- *     Double#toString(double)} respectively, then the value will be rounded
+ *     the string returned by {@link
+ *     Double#toString(double)}, then the value will be rounded
  *     using the {@linkplain java.math.RoundingMode#HALF_UP round half up
  *     algorithm}.  Otherwise, zeros may be appended to reach the precision.
  *     For a canonical representation of the value, use {@link
@@ -3512,19 +3518,16 @@ private void print(Formatter fmt, double value, Locale l) throws IOException {
             appendJustified(fmt.a, sb);
         }
 
-        // !Double.isInfinite(value) && !Double.isNaN(value)
+        // !Double.isInfinite(value) && !Double.isNaN(value) && value sign bit is 0
         private void print(Formatter fmt, StringBuilder sb, double value, Locale l,
-                           int flags, char c, int precision, boolean neg)
-            throws IOException
-        {
+                           int flags, char c, int precision, boolean neg) {
             if (c == Conversion.SCIENTIFIC) {
-                // Create a new FormattedFloatingDecimal with the desired
+                // Create a new FormattedFPDecimal with the desired
                 // precision.
                 int prec = (precision == -1 ? 6 : precision);
 
-                FormattedFloatingDecimal fd
-                        = FormattedFloatingDecimal.valueOf(value, prec,
-                          FormattedFloatingDecimal.Form.SCIENTIFIC);
+                FormattedFPDecimal fd = FormattedFPDecimal.valueOf(
+                        value, prec, FormattedFPDecimal.SCIENTIFIC);
 
                 StringBuilder mant = new StringBuilder().append(fd.getMantissa());
                 addZeros(mant, prec);
@@ -3552,13 +3555,12 @@ private void print(Formatter fmt, StringBuilder sb, double value, Locale l,
 
                 localizedMagnitudeExp(fmt, sb, exp, 1, l);
             } else if (c == Conversion.DECIMAL_FLOAT) {
-                // Create a new FormattedFloatingDecimal with the desired
+                // Create a new FormattedFPDecimal with the desired
                 // precision.
                 int prec = (precision == -1 ? 6 : precision);
 
-                FormattedFloatingDecimal fd
-                        = FormattedFloatingDecimal.valueOf(value, prec,
-                          FormattedFloatingDecimal.Form.DECIMAL_FLOAT);
+                FormattedFPDecimal fd = FormattedFPDecimal.valueOf(
+                        value, prec, FormattedFPDecimal.PLAIN);
 
                 StringBuilder mant = new StringBuilder().append(fd.getMantissa());
                 addZeros(mant, prec);
@@ -3587,9 +3589,8 @@ else if (precision == 0)
                     mant.append('0');
                     expRounded = 0;
                 } else {
-                    FormattedFloatingDecimal fd
-                        = FormattedFloatingDecimal.valueOf(value, prec,
-                          FormattedFloatingDecimal.Form.GENERAL);
+                    FormattedFPDecimal fd = FormattedFPDecimal.valueOf(
+                            value, prec, FormattedFPDecimal.GENERAL);
                     exp = fd.getExponent();
                     mant.append(fd.getMantissa());
                     expRounded = fd.getExponentRounded();

src/java.base/share/classes/jdk/internal/math/DoubleToDecimal.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -35,7 +35,7 @@
 /**
  * This class exposes a method to render a {@code double} as a string.
  */
-final public class DoubleToDecimal {
+public final class DoubleToDecimal {
     /*
      * For full details about this code see the following references:
      *
@@ -110,12 +110,13 @@ final public class DoubleToDecimal {
      */
     public static final int MAX_CHARS = H + 7;
 
-    private final byte[] bytes = new byte[MAX_CHARS];
+    private final byte[] bytes;
 
     /* Index into bytes of rightmost valid character */
     private int index;
 
-    private DoubleToDecimal() {
+    private DoubleToDecimal(boolean noChars) {
+        bytes = noChars ? null : new byte[MAX_CHARS];
     }
 
     /**
@@ -127,7 +128,28 @@ private DoubleToDecimal() {
      * @see Double#toString(double)
      */
     public static String toString(double v) {
-        return new DoubleToDecimal().toDecimalString(v);
+        return new DoubleToDecimal(false).toDecimalString(v);
+    }
+
+    /**
+     * Splits the decimal <i>d</i> described in
+     * {@link Double#toString(double)} in integers <i>f</i> and <i>e</i>
+     * such that <i>d</i> = <i>f</i> 10<sup><i>e</i></sup>.
+     *
+     * <p>Further, determines integer <i>n</i> such that <i>n</i> = 0 when
+     * <i>f</i> = 0, and
+     * 10<sup><i>n</i>-1</sup> &le; <i>f</i> &lt; 10<sup><i>n</i></sup>
+     * otherwise.
+     *
+     * <p>The argument {@code v} is assumed to be a positive finite value or
+     * positive zero.
+     * Further, {@code fd} must not be {@code null}.
+     *
+     * @param v     the finite {@code double} to be split.
+     * @param fd    the object that will carry <i>f</i>, <i>e</i>, and <i>n</i>.
+     */
+    public static void split(double v, FormattedFPDecimal fd) {
+        new DoubleToDecimal(true).toDecimal(v, fd);
     }
 
     /**
@@ -143,11 +165,11 @@ public static String toString(double v) {
      */
     public static Appendable appendTo(double v, Appendable app)
             throws IOException {
-        return new DoubleToDecimal().appendDecimalTo(v, app);
+        return new DoubleToDecimal(false).appendDecimalTo(v, app);
     }
 
     private String toDecimalString(double v) {
-        return switch (toDecimal(v)) {
+        return switch (toDecimal(v, null)) {
             case NON_SPECIAL -> charsToString();
             case PLUS_ZERO -> "0.0";
             case MINUS_ZERO -> "-0.0";
@@ -159,7 +181,7 @@ private String toDecimalString(double v) {
 
     private Appendable appendDecimalTo(double v, Appendable app)
             throws IOException {
-        switch (toDecimal(v)) {
+        switch (toDecimal(v, null)) {
             case NON_SPECIAL:
                 char[] chars = new char[index + 1];
                 for (int i = 0; i < chars.length; ++i) {
@@ -191,7 +213,7 @@ private Appendable appendDecimalTo(double v, Appendable app)
      *     MINUS_INF       iff v is NEGATIVE_INFINITY
      *     NAN             iff v is NaN
      */
-    private int toDecimal(double v) {
+    private int toDecimal(double v, FormattedFPDecimal fd) {
         /*
          * For full details see references [2] and [1].
          *
@@ -207,6 +229,10 @@ private int toDecimal(double v) {
         if (bq < BQ_MASK) {
             index = -1;
             if (bits < 0) {
+                /*
+                 * fd != null implies bytes == null and bits >= 0
+                 * Thus, when fd != null, control never reaches here.
+                 */
                 append('-');
             }
             if (bq != 0) {
@@ -217,16 +243,16 @@ private int toDecimal(double v) {
                 if (0 < mq & mq < P) {
                     long f = c >> mq;
                     if (f << mq == c) {
-                        return toChars(f, 0);
+                        return toChars(f, 0, fd);
                     }
                 }
-                return toDecimal(-mq, c, 0);
+                return toDecimal(-mq, c, 0, fd);
             }
             if (t != 0) {
                 /* subnormal value */
                 return t < C_TINY
-                       ? toDecimal(Q_MIN, 10 * t, -1)
-                       : toDecimal(Q_MIN, t, 0);
+                       ? toDecimal(Q_MIN, 10 * t, -1, fd)
+                       : toDecimal(Q_MIN, t, 0, fd);
             }
             return bits == 0 ? PLUS_ZERO : MINUS_ZERO;
         }
@@ -236,7 +262,7 @@ private int toDecimal(double v) {
         return bits > 0 ? PLUS_INF : MINUS_INF;
     }
 
-    private int toDecimal(int q, long c, int dk) {
+    private int toDecimal(int q, long c, int dk, FormattedFPDecimal fd) {
         /*
          * The skeleton corresponds to figure 7 of [1].
          * The efficient computations are those summarized in figure 9.
@@ -301,7 +327,7 @@ private int toDecimal(int q, long c, int dk) {
             boolean upin = vbl + out <= sp10 << 2;
             boolean wpin = (tp10 << 2) + out <= vbr;
             if (upin != wpin) {
-                return toChars(upin ? sp10 : tp10, k);
+                return toChars(upin ? sp10 : tp10, k, fd);
             }
         }
 
@@ -316,14 +342,14 @@ private int toDecimal(int q, long c, int dk) {
         boolean win = (t << 2) + out <= vbr;
         if (uin != win) {
             /* Exactly one of u or w lies in Rv */
-            return toChars(uin ? s : t, k + dk);
+            return toChars(uin ? s : t, k + dk, fd);
         }
         /*
          * Both u and w lie in Rv: determine the one closest to v.
          * See section 9.3 of [1].
          */
         long cmp = vb - (s + t << 1);
-        return toChars(cmp < 0 || cmp == 0 && (s & 0x1) == 0 ? s : t, k + dk);
+        return toChars(cmp < 0 || cmp == 0 && (s & 0x1) == 0 ? s : t, k + dk, fd);
     }
 
     /*
@@ -342,7 +368,7 @@ private static long rop(long g1, long g0, long cp) {
     /*
      * Formats the decimal f 10^e.
      */
-    private int toChars(long f, int e) {
+    private int toChars(long f, int e, FormattedFPDecimal fd) {
         /*
          * For details not discussed here see section 10 of [1].
          *
@@ -353,6 +379,10 @@ private int toChars(long f, int e) {
         if (f >= pow10(len)) {
             len += 1;
         }
+        if (fd != null) {
+            fd.set(f, e, len);
+            return NON_SPECIAL;
+        }
 
         /*
          * Let fp and ep be the original f and e, respectively.