EIP-7823: Set upper bounds for MODEXP --- HUB side

[OlivierBBB]

Note

Implements MODEXP common rows (byte-size extraction, leading-word, pricing) with EIP‑7823 upper-bound checks, updates success flow to use normalized sizes, and refactors OOB lead/xbs logic.

• Hub/Constraints — MODEXP common processing:
  • New rows in common/:
    • __01__call_data_size_analysis_row.lisp: OOB modexp-cds; exposes extract-{b,e,m}bs.
    • __02__bbs_extraction_row.lisp, __03__ebs_extraction_row.lisp, __04__mbs_extraction_row.lisp:
      • Set MISC/MMU flags; MMU right‑padded word extraction; OOB modexp-xbs.
      • Expose {b,e,m}bs-(hi|lo), within/out‑of‑bounds bits, and normalized sizes; compute max-mbs-bbs and all-byte-sizes-are-in-bounds.
    • __05__exponent_leading_word_extraction_and_analysis_row.lisp:
      • Coordinate EXP/MMU/OOB for leading word; MMU mload; OOB modexp-lead; expose cutoffs and modexp-full-log.
    • __06__pricing_row.lisp: OOB modexp-pricing; expose RAM success/return gas.
    • generalities.lisp: standard precondition; exclude hub-known failure.
    • justifying_hub_predictions.lisp: tie success and return gas to pricing outputs gated by bounds.
  • Constants: rename row offsets to *-extraction-and-analysis.
• Hub/Success path (success.lisp):
  • Use normalized {b,e,m}bs across base/exponent/modulus extraction.
  • Replace fixed 512 with EIP_7823_MODEXP_UPPER_BYTE_SIZE_BOUND for result copy; adjust offsets and return-data sizes.
• OOB:
  • modexp/lead.lisp: rename load-lead → extract-leading-word; update justification accordingly.
  • modexp/xbs.lisp: refactor comparison helpers and prediction bits; adjust max(xbs,ybs) setting logic and bounds bits.

^{Written by Cursor Bugbot for commit 6bcb9fc. This will update automatically on new commits. Configure here.}

[cursor]

Bug: OOB Flag Check Misplaced in Precompile Step

The function precompile-processing---MODEXP---call-OOB-on-leading-word-row incorrectly checks misc/MMU_FLAG instead of misc/OOB_FLAG. This is a copy-paste error from the line above. The function name indicates it should check if the OOB module is being called, and it's used in a constraint (line 37) that requires it to equal 1, meaning OOB should always be called on this row. However, it's actually checking the MMU flag, which will cause incorrect behavior when the MMU flag and OOB flag have different values.

 

[cursor]

Bug: Broken bounds check for MODEXP parameters

The constraint forces prc-modexp-xbs---xbs-is-LEQ-the-MODEXP-upper-bound to always equal 1, preventing the system from detecting out-of-bounds byte sizes. This makes xbs-out-of-bounds always 0 and breaks the bounds checking mechanism for MODEXP parameters, allowing invalid calls that exceed EIP_7823_MODEXP_UPPER_BYTE_SIZE_BOUND to pass validation.