REAL 64 (issues)

Revision as of 10:55, 17 November 2006 by Patrickr (Talk | contribs) (typos)

This page describes issues with the current implementation of REAL_64 in comparison to the interface description or desired output when nothing is specified.

is_equal and NaN

The floating point standard says that 'NaN = NaN' is false. But in order to uphold the postcondition of 'NaN.twin' which says that 'Result.is_equal (Current)' the comparison with 'is_equal' should yield true.

At the moment 'is_equal' for reals is optimized in the compiler and is replaced by '=' and thus the postcondition of 'twin' is violated.

floor, ceiling, rounded and truncated_to_integer

Currently when doing a 'floor', 'ceiling', 'rounded' or 'truncate_to_integer' with a number which is too large (e.g. 2^31) the result is {INTEGER}.min_value.

The change in the sign is a not expected behavior and violates (informal) contracts.

divisible

By providing NaN and INF every real value can be divided by every other real value. Thus a call of 'divisible' should always return true. This arises again in INTEGER.infix "/". A call to 12 / 0 is not allowed by the current contract but should just return INF.

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