8229845: Decrease memory consumption of BigInteger.toString()

[Ivan Gerasimov]

Hi Brian!

Would it make sense to add an argument `digits` to smallToString (like 
the same named argument of toString, the minimum number of digits to pad 
to), so it could zero-pad the result itself?

This way we could avoid inserting zeros into the middle of a 
StringBuilder after a call to smallToString.

With kind regards,
Ivan

On 8/20/19 11:51 AM, Brian Burkhalter wrote:
> Delta [1] and revised [2] patches:
>
> [1] http://cr.openjdk.java.net/~bpb/8229845/webrev.00-01/
> [2] http://cr.openjdk.java.net/~bpb/8229845/webrev.01/
>
>> On Aug 20, 2019, at 1:05 AM, Aleksey Shipilev <shade at redhat.com 
>> <mailto:shade at redhat.com>> wrote:
>>
>> On 8/19/19 10:08 PM, Brian Burkhalter wrote:
>>> [2]http://cr.openjdk.java.net/~bpb/8229845/webrev.00/
>>
>> Two drive-by comments:
>>
>> *) It seems the "signum == 0" case in smallToString is regressing? 
>> Before, it just returned the
>> constant-pooled "0", now it goes via StringBuilder;
>
> Yes, and I don’t see any way not to have it do so. Note that due to 
> lines 3933-3936 in [2] this case will never be hit for values which 
> have no more than 20 ints in their magnitude, i.e., those which do not 
> recurse in toString(BigInteger,StringBuilder,int,int).
>
>> *) This might be "static final", while we are at it:
>>
>> 4109     private static String[] zeros = new String[64];
>
> Above made final at L4111 in [2].
>
>> On Aug 20, 2019, at 10:28 AM, Ivan Gerasimov 
>> <ivan.gerasimov at oracle.com <mailto:ivan.gerasimov at oracle.com>> wrote:
>>
>> While we're here.
>>
>> On 8/20/19 1:05 AM, Aleksey Shipilev wrote:
>>>  *) This might be "static final", while we are at it:
>>>
>>> 4109     private static String[] zeros = new String[64];
>>>
>> It may make sense to create the only string as
>>
>> private static final String zeros = "0".repeat(63);
>
> Changed at L4111 in [2].
>
>> and then replace all
>>
>> sb.append(zeros[x]) with sb.append(zeros, 0, x) and
>
> L4006 in [2].
>
>> sb.insert(pos, zeros[x]) with sb.insert(pos, zeros, 0, x).
>
> L4049 and L4054 in [2].
>
>> The difference would be in one extra bounds check, and as both 
>> append() and insert() are relatively expensive, this check would 
>> hardly be noticeable.
>
> Thanks,
>
> Brian

-- 
With kind regards,
Ivan Gerasimov