src/share/classes/sun/misc/FloatingDecimal.java

rev 6572 : 8024356: Double.parseDouble() is slow for long Strings
Summary: Clamp nDigits to MAX_NDIGITS.
Reviewed-by: bpb, drchase, shade
Contributed-by: Dmitry Nadezhin <dmitry.nadezhin@oracle.com>

*** 68,77 ****
--- 68,86 ----
      static final int    maxDecimalDigits = 15;
      static final int    maxDecimalExponent = 308;
      static final int    minDecimalExponent = -324;
      static final int    bigDecimalExponent = 324; // i.e. abs(minDecimalExponent)
  
+     //
+     // The value below is chosen as a conservative threshold. It
+     // can be demonstrated that a decimal ulp less than 10^(-1075)
+     // is enough to guarantee correctness. Compensation is also made
+     // for the binary mantissa which takes 53 binary digits, or
+     // 17 decimal ones. Hence 1075 + 17 =~ 1100.
+     //
+     static final int    MAX_NDIGITS = 1100;
+ 
      static final long   highbyte = 0xff00000000000000L;
      static final long   highbit  = 0x8000000000000000L;
      static final long   lowbytes = ~highbyte;
  
      static final int    singleSignMask =    0x80000000;
*** 1466,1475 ****
--- 1475,1488 ----
               * The hard part is adjusting it, by comparison
               * with FDBigInt arithmetic.
               * Formulate the EXACT big-number result as
               * bigD0 * 10^exp
               */
+             if (nDigits > MAX_NDIGITS) {
+                 nDigits = MAX_NDIGITS + 1;
+                 digits[MAX_NDIGITS] = '1';
+             }
              FDBigInt bigD0 = new FDBigInt( lValue, digits, kDigits, nDigits );
              exp   = decExponent - nDigits;
  
              correctionLoop:
              while(true){