# [racket-dev] Subnormal numbers?

I can't answer the question about underflow. But if you don't mind
installing a nightly build of Racket, you get the (currently
undocumented) module `unstable/flonum', which exports these:
flonum->bit-field
bit-field->flonum
flonum->ordinal ; number of flonums away from 0 (+ or -)
ordinal->flonum
flstep ; the flonum n steps away (by ordering fl<)
flnext ; next largest flonum (by ordering fl<)
flprev ; next smallest flonum (by ordering fl<)
-max.0 ; negative flonum with greatest non-infinite magnitude
-min.0 ; negative flonum with smallest nonzero magnitude
+min.0 ; positive flonum with smallest nonzero magnitude
+max.0 ; positive flonum with greatest non-infinite magnitude
Also, the `plot' module in the nightly build deals just fine with
intervals that are too small to represent using flonums. For example, to
illustrate floating-point discretization and the density of flonums at
different ranges:
#lang racket
(require plot unstable/flonum)
(plot (function (λ (x) (inexact->exact (sin x)))
(flstep 0.0 -10) (flstep 0.0 10)))
(- (flonum->ordinal 1.0) (flonum->ordinal 0.0))
(- (flonum->ordinal 2.0) (flonum->ordinal 1.0))
(- (flonum->ordinal 3.0) (flonum->ordinal 2.0))
(- (flonum->ordinal +max.0) (flonum->ordinal 1.0))
(parameterize ([plot-x-ticks (log-ticks #:base 2)])
(plot (function (compose flonum->ordinal exact->inexact) 1.0 8.0)))
Neil T
On 11/29/2011 09:32 AM, J. Ian Johnson wrote:
>* I'm currently proctoring the freshmen's lab on inexact numbers and was curious how to denote subnormal numbers in Racket.
*>* Turns out that's not possible, since there is no underflow. Why does Racket follow the old standard of representing underflow with inexact zero?
*>* I imagine changing it now would break a lot of code, but I'm just curious.
*>* -Ian
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