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Re: reading NaNs

This page is part of the web mail archives of SRFI 77 from before July 7th, 2015. The new archives for SRFI 77 contain all messages, not just those from before July 7th, 2015.

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.)

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