libgcj/1615: java.math.BigInteger.modPow produces bogus results w/ certain input data

[mjr at statesmean dot com]

>Number:         1615
>Category:       libgcj
>Synopsis:       java.math.BigInteger.modPow produces bogus results w/ certain input data
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jan 11 03:16:01 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     Mark J. Roberts
>Release:        current cvs
>Organization:
>Environment:

>Description:
Test program produces differing results between gcj and JDK
when doing:
    BigInteger A = Z.modPow(X,Y);
With certain values the results are quite different. This
did not emerge when I tried smaller values (even quite big 
smaller values) but only with these big Diffie-Hellman-sized
ones. With some similarly-sized ones, I could not reproduce 
the error, so perhaps it's related to improper rounding?
>How-To-Repeat:
Run attached test.  The results are different between gcj and the JDK.

[root@rm03-24-131-185-22 /freenet]# gcj --main=EvilBug -o evilbug EvilBug.java
[root@rm03-24-131-185-22 /freenet]# ./evilbug
76475944278426898748735231384095480813900840993607065582220349895865809085142942
61493127493459662105163340290092559057818974002325805972134344425347604257231501
46381041759288915308787564035524024468249392955598305929492513236493499334514618
56156175697510863031755311205211843476729890389330266393681960156153
[root@rm03-24-131-185-22 /freenet]# javac EvilBug.java
[root@rm03-24-131-185-22 /freenet]# java EvilBug
89040229313686098274750802637193802904787850353791629688385431482589769348345172
94453965836689358745685734731231497412444569542388500553341455909980169961229423
58615700657742229111808904170093854558265607737415202978848504603247816209744675
60905975577765401911117379967692495136423710471201230243826129276993
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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