Modexp revision

[hecmas]

This PR introduces several corrections and optimizations to the modexp folder:

• Array capacity of modexp has been increased from 16 to 32. This means that we can now carry a modexp computation of at most 8192 bits.
• array _utils folder has been removed. Functions inside it (i.e., array_compare) are now performed directly in the array arithmetic operations. This avoids the unnecessary actions of copying memory from one place to another if its not needed.
• All lops in arithmetic operations have been split to be able to exploit particularities inside them. For example, putting aside the first row computation of an array_mul_long avoids the need of cleaning the previous output of a previous long multiplication.
• Counters are now more precise and more high level that before, controlling better possible malicious behaviors.
• Some assumptions have been introduced to the code. For instance, now both array_div_short and array_div_long assume that the denominator cannot be zero (which is a save assumption in the context of modexp).
• Merged PR Adding division by two #356 into it. See it for details.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[ignasirv]

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