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Compiler.NaturalMagnitudeArithmetic

packages/compiler/src/Compiler/NaturalMagnitudeArithmetic.alpha

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def · lines 298–300

magnitudeSubtractBorrow

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Saturating subtraction over canonical digits. Compare before borrowing so underflow produces canonical zero. All Nat arithmetic is bounded to 0..19; the numeric value is never expanded to a unary natural.
298def magnitudeSubtractBorrow =
299  (lambda unrestricted digit : Byte .
300    (lambda unrestricted subtrahend : Nat . (nat-less-than (byte-to-nat digit) subtrahend)))

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