Add modPow tests.

Add modPow tests.
Fix selection of modular reduction algorithm for modPow.
Remove bad assert and fix digits array length in classic modular reduction.

R=srdjan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=43817

[regis, 2015-02-13 01:01:30]

regis@google.com changed reviewers:
+ srdjan@google.com

[regis, 2015-02-13 01:01:31]

I sorted out the issue with the new modPow tests. In order to apply Montgomery
reduction in x.modPow(e, m), the absolute value of x has to be smaller than the
modulus m, which is always guaranteed in RSA. This is why we did not check.

Thanks,
Regis

[srdjan, 2015-02-17 19:15:37]

lgtm

https://codereview.chromium.org/918403002/diff/1/runtime/lib/bigint.dart
File runtime/lib/bigint.dart (right):

https://codereview.chromium.org/918403002/diff/1/runtime/lib/bigint.dart#newc...
runtime/lib/bigint.dart:1354: _Reduction z = (cannot_use_montgomery || e_bitlen
< 8) ?
Dart style guide says to use camelBack instead of _ for variable and function
naming.

[regis, 2015-02-17 19:29:34]

New patchsets have been uploaded after l-g-t-m from srdjan@google.com

[regis, 2015-02-17 19:32:15]

Thanks!

https://codereview.chromium.org/918403002/diff/1/runtime/lib/bigint.dart
File runtime/lib/bigint.dart (right):

https://codereview.chromium.org/918403002/diff/1/runtime/lib/bigint.dart#newc...
runtime/lib/bigint.dart:1354: _Reduction z = (cannot_use_montgomery || e_bitlen
< 8) ?
On 2015/02/17 19:15:37, srdjan wrote:
> Dart style guide says to use camelBack instead of _ for variable and function
> naming.

I renamed the new variable cannot_use_montgomery to cannotUseMontgomery, but not
the previously existing one. If you think it is important, I'll do a global
rename.

[regis, 2015-02-17 19:32:37]

Committed patchset #2 (id:20001) manually as r43817 (presubmit successful).