limit modexp call to 8192 bit inputs

[hexoscott]

To tackle #1385

[krlosMata]

The behavior should be slightly different since we tried to mimic ethereum specification and some special cases are handled before checking the lenght.
Some input values, returns directly before checking the input bits: https://github.com/0xPolygonHermez/zkevm-rom/blob/develop-durian/main/precompiled/pre-modexp.zkasm#L197

• if module size is 0, return 0
• then if base size is 0, check module size is lomnger than 8192 (revert), otherwise return 0
• check the three lenghts

[krlosMata]

LGTM xD
Altough this code un reachable now --> https://github.com/0xPolygonHermez/cdk-erigon/pull/1391/files#diff-2808ea960ae76bcf0a3ce1f869a900dd594726cf7ea0c32ade4306b53f330dc5R427

[hexoscott]

hmmmm

[hexoscott]

The unreachable code is effectively the same so I've combined the statements now

[krlosMata]

if modulo size is 0, the precompile returns 0 and it consumes GAS. This case is not handled.
if base size is 0 & modsize < 8192, it should also return 0 and consume GAS. This case is not handled.

[hexoscott]

These are the revert cases to return a 0 gas so that we don't consume any. Anything else consumes gas as it would normally, unless I'm missing something?

[krlosMata]

comment is not right

[hexoscott]

I have removed this comment. It was there from the original erigon implementation.