Re: random real number between 0 (inclusive) and 1 (inclusive)
Piotr Kobzda wrote:
Patricia Shanahan wrote:
Piotr Kobzda wrote:
[...]
I still have some doubts, I don't like "rand.nextDouble()*MILTIPLIER"
part -- I've a feeling it somehow favors small doubles, but I may be
wrong, so never mind...
Take a look at the nextDouble code. It works by collecting a total of 53
bits from next(26) and next(27), concatenating them to form a double in
the range 0 through MULTIPLIER-1, and then double precision dividing the
result by MULTIPLIER. The multiplication just recovers the uniformly
distributed [0,MULTIPLIER) long.
OK, you right -- my mistake in analyzing... However, there is no need
for that (long) -> (double) -> (long) conversion, which is 1:1 in this
case.
The intent of the conversion was to do the arithmetic in long, rather
than double.
The issue is floating point rounding. Adding two longs in the range
[0,2**53-1] is an exact operation, because the result has no more than
54 significant bits. In double, it can cause rounding, because double
only supports 53 significant bits. After the subtraction, the result is
guaranteed to be exactly representable in double.
I have not yet analyzed your latest solution from the point of view of
floating point rounding. Did you take it into account in designing the
solution?
Patricia
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