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fix: brillig signed division #356
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kevaundray
approved these changes
Jun 9, 2023
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Description
Problem*
Signed division wasn't working with the bit sizes of the numbers involved.
The previous algorithm for to_signed was trying to check if the number was >= than
2.pow(NUM_BITS), when it should be2.pow(NUM_BITS - 1)for example, with 4 bits, -1 is 1111, which is 15 in unsigned form, which is less than 2**4 so it was treated as positive.
The same happened with to_unsigned, where -1 in 4 bits was transformed into -1 +
2.pow(NUM_BITS + 1)which is 31 instead of 15.Summary*
Example
Before:
After:
Additional Context
PR Checklist*
cargo fmton default settings.BEGIN_COMMIT_OVERRIDE
fix(brillig): Correct signed division implementation (#356)
END_COMMIT_OVERRIDE