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Re: reading NaNs



Aubrey Jaffer wrote:
Are you suggesting a single NaN or multiple distinct NaNs?

To support existing IEEE-754 hardware, R6RS must not mandate multiple
distinct NaNs.  But specifying a singular NaN prevents implementations
from fully supporting IEEE-754 in the future.

All hardware should recognize all NaNs. Therefore, allowing NaNs to be generated with aribitrary bit patterns is not a problem. However, different hardware need not generate the same NaNs for identical operands.

However, I still think we need a read syntax. Suppose program A calculates a value and writes it to a file and program B reads the value from the file and uses it. Is is not useful for program A to be able to communicate to program B that it got a NaN? This would suggest we need a write syntax and a read syntax for NaNs. (Whether this syntax should specify and preserve the bit patterns is another argument.)

Alan
--
Dr Alan Watson
Centro de Radioastronomía y Astrofísica
Universidad Astronómico Nacional de México