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Chris Tate
dc9b60656d
`a[i * n + k]` with int32 operands kept the index in doubles whenever the product's range could pass 2^53: integer arithmetic needs a proven safe range, and an int32 product can reach 2^62. Every access then converted the double back with an exactness test. Such arithmetic now also carries a wide view: the exact integer as an i64, the magnitude it is bounded by, and a threshold below which the double equals it. A product of two exact integers equals its double below 2^53 in magnitude, and a sum or difference of a wide view exact below T and an exact integer of magnitude at most B equals its double below min(T - B, 2^53). Every i64 result stays within 2^62 + 2^53, so none wraps. An array index below a length or capacity is below 2^32, under every threshold kept, so the dense array guards and local array reads compare the wide view, unsigned, with the array's counts and skip the round trip. Any index that fails those comparisons, including every index whose double rounds, takes the double's path as before. Typed arrays and strings are unchanged.