Add $crc32() function for CRC-32 checksum computation

[Copilot]

• Understand the problem statement: Add CRC/checksum support to Emboss
• Add CRC32 function support to Emboss compiler and runtime
• Add unit tests for CRC-32 implementation
  • Tests for empty input
  • Tests for known test vectors (e.g., "123456789" -> 0xCBF43926)
  • Tests for single bytes (0x00, 0xFF)
  • Tests for multi-byte sequences
  • Tests for lookup table correctness
  • Tests for longer messages

Original prompt

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This section details on the original issue you should resolve

<issue_title>CRC/Checksum Support</issue_title>
<issue_description>This issue was copied from the upstream repository google/emboss.

Original issue: google#31
Original state: open, created at: 2022-02-15T23:11:57Z, updated at: 2024-12-18T23:14:41Z, by @reventlov

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Original description

CRCs and checksums are common enough that there should be built-in support for verifying and setting CRCs/checksums to the correct value. One possible implementation would be $crc(range : UInt:8[]) and $checksum(range : UInt:8[]) functions which can be used in [requires].

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Discussion (copied comments)

Comment by @AaronWebster on 2022-03-14T17:52:47Z:

Would be useful if the type could be specified, e.g. $checksum(type : CRC32C, range : UInt:8[]). Maybe more useful if Emboss had a way of supporting a type whose value was computed using a user-defined function.

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Comment by @reventlov on 2022-03-14T19:44:32Z:

I was thinking $crc() and $checksum() specifically so that you don't have to specify which algorithm as a parameter. User-defined functions would be nice, but a much bigger feature to design.

$crc() should have an optional parameter for the polynomial, though. Probably default to the IEEE polynomial, at least for CRC-32.

We also need some way to specify how many bits are in the CRC/checksum.

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Comment by @AaronWebster on 2022-03-15T17:28:34Z:

pycrc might be a good fit using its c code generator. Supports arbitrary polynomials/bits/endianness/etc.

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Comment by @reventlov on 2022-03-15T20:50:24Z:

Something like CRC_t is probably better: a C++ template takes advantage of the C++ compiler to avoid having multiple copies of the same code or extra unneeded code in the final binary, even across translation units.

We would need to import a copy and shove it into a different namespace to avoid potential version skew between the copy in Emboss and a copy that happens to be used in application code.

Also, it would be good to add some options to the C++ backend or site_defines.h to allow applications to pick their own implementation. I assume a lot of embedded projects will already have a CRC library somewhere; we should use theirs when possible instead of adding binary image size.

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</issue_description>

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

• Fixes CRC/Checksum Support #87

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[AaronWebster]

@copilot wright unit tests for the CRC implementation

[Copilot]

@copilot wright unit tests for the CRC implementation

Added unit tests for the CRC-32 implementation in commit 457af49. The tests cover:

• Empty input
• Well-known test vector "123456789" → 0xCBF43926
• Single byte inputs (0x00, 0xFF)
• Multi-byte sequences
• Lookup table correctness verification
• Longer message ("The quick brown fox...")

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