[Cfp-interest 2044] Re: Underflow

[Jim Thomas]

> On Jun 24, 2021, at 6:44 AM, Fred J. Tydeman <tydeman at tybor.com> wrote:
> 
> N2746 is proposing for the definition of underflow:
> 
> [6] The result underflows if a nonzero result value with ordinary
> accuracy would have magnitude (absolute value) no larger than the
> minimum normalized number in the type.249
> 
> I would prefer:
> 
> [6] The result underflows if a nonzero result value, before rounding,
> would have magnitude (absolute value) less than the minimum normalized
> number in the type.249

This seems to assume a model where a wider precision result is computed and then rounded to the result format. C doesn't have that model for math functions.

> 
> 
> Also, I believe that "inexact" should be added to the footnote as:
> 
> 249)The term underflow here is intended to encompass both "gradual
> underflow" as in IEC 60559 and also "flush-to-zero" underflow. IEC
> 60559 underflow can occur in cases where the magnitude of the inexact
> rounded result equals the minimum normalized number in the format.

Change “the inexact” to “an inexact”.

- Jim Thomas


> 
> 
> ---
> Fred J. Tydeman        Tydeman Consulting
> tydeman at tybor.com      Testing, numerics, programming
> +1 (702) 608-6093      Vice-chair of PL22.11 (ANSI "C")
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