JDK 7u-dev review request 8024356: Double.parseDouble() is slow for long Strings
Dmitry Nadezhin
dmitry.nadezhin at gmail.com
Thu Sep 12 18:10:35 UTC 2013
Aleksey, I like your wording of the comment. Thank you very much.
I would reformulate a little:
<<<
We can demonstrate (<link>) that decimal ulp should be less than 10^(-1075)
to guarantee correctness
===
We can demonstrate (<link>) that decimal ulp less than 10^(-1075) is enough
to guarantee correctness.
>>
because decimal ulp may be larger than 10^(-1075) for some inputs.
For example, for decimal string
"1.1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
binary half-ulp is 2^(-53)
and decimal ulp 10^(-53) is enough .
On Thu, Sep 12, 2013 at 6:32 PM, Aleksey Shipilev <
aleksey.shipilev at oracle.com> wrote:
> On 09/12/2013 09:17 AM, Dmitry Nadezhin wrote:
> > The patch is correct when decimal ULP of kept digits is pow(10,-1075)
> > of less. pow(2,53) has 17 decimal decimal digits. MAX_NDIGITS = 1100
> > > 1075 + 17 .
>
> OK. That makes more sense. Can we please add the short comment in the
> code (maybe next time around)?
>
> I expected to see something like "The value below is chosen as the
> conservative threshold. We can demonstrate (<link>) that decimal ulp
> should be less than 10^(-1075) to guarantee correctness; we also
> compensate for binary mantissa which takes 53 binary digits, or 17
> decimal ones. Hence, 1075+17 =~ 1100."
>
> -Aleksey.
>
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