Add integer division and modulus operators to expression sublanguage

[Copilot]

Adds / (floored division) and % (floored modulus) operators to the Emboss expression language, enabling expressions like size / 4 and offset % alignment.

Semantics

Uses floored division (Python's // semantics), not truncated division (C's /). This ensures the identity a == (a / b) * b + (a % b) holds for all integers:

10 / 3 == 3      -10 / 3 == -4
10 % 3 == 1      -10 % 3 == 2

Changes

• Tokenizer/Parser: Added / and % tokens and grammar productions at same precedence as *
• IR: Added DIVISION and MODULUS to FunctionMapping enum
• Type checking: Integer arguments required, integer result
• Bounds computation: Computes conservative bounds excluding zero from divisor range; constant expressions evaluated exactly
• C++ runtime: FlooredDivisionOperation and FlooredModulusOperation with div-by-zero guards
• Code generation: Maps to FlooredDivision and FlooredModulus support functions

Example

struct Packet:
  0 [+1]  UInt  total_size
  1 [+1]  UInt  alignment
    [requires: 1 <= this]
  
  let aligned_size = (total_size + alignment - 1) / alignment * alignment
  let padding = aligned_size % alignment

Original prompt

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This section details on the original issue you should resolve

<issue_title>Support Integer Division and Modulus in the Emboss Expression Sublanguage</issue_title>
<issue_description>This issue was copied from the upstream repository google/emboss.

Original issue: google#41
Original state: open, created at: 2022-04-19T19:40:27Z, updated at: 2024-12-18T23:14:42Z, by @reventlov

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Original description

Emboss should support integer division and modulus.

Note that there are several subtleties to these operations. reventlov to provide a proper design doc.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Support Integer Division and Modulus in the Emboss Expression Sublanguage #82

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