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bugc: point at packed words' parts as their own regions - #398
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A local of bytes or a string in calldata is one word: the offset in its high 16 bytes, the length in its low 16. Name each half as its own region (x-offset, x-length) and have the calldata region read them, instead of reading the whole word and taking ~quotient and ~remainder by 2^128.
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A local of bytes or a string in calldata is held as one word: the offset of the bytes in its high 16 bytes and their length in its low 16 bytes. Its pointer used to name that whole word and have the
calldataregion compute its offset and length as~quotientand~remainderof the word by 2^128.Now each half of the word is a region of its own,
x-offset(bytes 0–15 of the word) andx-length(bytes 16–31), in memory or on the stack, andx-datareads them directly:{ "group": [ { "name": "text-offset", "location": "stack", "slot": 2, "offset": 0, "length": 16 }, { "name": "text-length", "location": "stack", "slot": 2, "offset": 16, "length": 16 }, { "name": "text-data", "location": "calldata", "offset": { "~read": "text-offset" }, "length": { "~read": "text-length" } } ] }The whole-word region
xis gone, since nothing reads it any more. Code generation is unchanged, and the pointers read the same bytes as before at every level. The case study and the soundness harness are updated to match.