+restrictions on long
+--------------------
+
+Java's 64-bit long type is not supported in JavaScript. There is no Int64Array in JavaScript,
+and 0x20000000000000 + 1 evaluates to 0x20000000000000, not 0x20000000000001.
+(Likewise, -0x20000000000000 - 1 is left unchanged.)
+
+The largest "integer" value in JavaScript is 9007199254740991 (9.007199254740991E13, or 0x1FFFFFFFFFFFFFF).
+Effectively, you get to use only 53 bits of the long, not 64. Trying to set a long larger than
+0x1FFFFFFFFFFFFFF or smaller than -0x1FFFFFFFFFFFFFF will result in a NumberFormatException.
+
+The transpiler handles conversion to long the same as Java for all cases other than from double.
+
+For small double values, there is no problem, and, in fact, this is a known trick used to round
+doubles and floats toward zero:
+
+double d;
+d = (long) 3.8;
+assert(d == 3);
+d = (long) -3.8;
+assert(d == -3);
+
+SwingJS will evaluate (long) d as 0 for d > 9007199254740991
+or d < -9007199254740991, same as Java returns for Double.NaN.
+So, in Java we have:
+
+ assert(((long) Double.NaN) == 0);
+ assert(((int) Double.NaN) == 0);
+ assert(((long) Float.NaN) == 0);
+ assert(((int) Float.NaN) == 0);
+
+and also, in JavaScript only, we also have:
+
+ double d = 0x2000000000000L;
+ assert(((long) d) == 0);
+
+
+restrictions on BitSet and Scanner
+----------------------------------
+
+Because of the issue of long being only 53 bits, any time a method returns a long value, considerations must
+be made as to whether this will work in JavaScript. In particular, BitSet and Scanner have issues.
+
+In SwingJS, java.util.BitSet has been implemented as a 32-bit integer-based bitset. This was no problem in
+Java 6, but starting with Java 7, a method was added to BitSet that allows for the extraction of the
+underlying long[] word data. This is not work in JavaScript. Instead, SwingJS java.util.Bitset.toLongArray() will deliver
+32-bit int[] data.
+
+SwingJS Scanner has hasNextLong() and nextLong(), and although it will scan through long numbers,
+Scanner will choke on long numbers greater than the JavaScript 53-bit limit. hasNextLong() will
+return false, and nextLong() will throw an InputMismatchException triggered by the NumberFormatException
+thrown by Long.parseLong().
+
+
git://source.jalview.org / jalview.git / commitdiff