On Aug 4, 8:35 am, "Len Lawrence" <l... / tarazed.demon.co.uk> wrote:
> I am starting to recode several home applications in Ruby/GTK2 after
> 16 years of Tcl/Tk and a foray into Ruby/Tk territory.  The simplest
> case would be my sidereal time widget which includes an Stime class,
> severely pruned below to show the to_s method (which has been altered
> to investigate the faulty behaviour described later).
>
> ----------------------------------------------------------------
>
> require 'date'
>
> class Stime
>
>   def to_s ( siderealtime )
>
>     z = siderealtime / 24.0
> #    h = (24.0 * z).to_i
>     c = Date.day_fraction_to_time( z )
>     c[3] *= 86400.0
>     c[2] += c[3]
>     c[3] = nil
> #    c[0] = h
>     sprintf( "%02d:%02d:%06.3f", c[0],c[1],c[2] )
>
>   end
>
> end
>
> puts stime.to_s( 9.334 )
> puts stime.to_s( 13.603 )
> t = 14.603
> puts sprintf( "whatever = %06.3f = %s\n", t, stime.to_s( t ) )
> puts stime.to_s( 18.765 )
>
> ----------------------------------------------------------------
>
> Results:
>
> 09:20:02.400
> 13:36:10.800
> whatever = 14.603 = 13:36:10.800   ???
> 18:45:54.000
>
> I have established by trying a few values within the range 13.999 to
> 15.000 that the error is confined to the range 14.000 to 14.999.  The
> symptoms are the same on two 64-bit machines, one AMD Opteron (2) and
> an Intel Core Duo.  It ain't rational.  Anybody ever seen anything
> like this?
>
> If the two commented lines are uncommented the to_s method always
> returns the correct hour value in the string.
> Date#day_fraction_to_time calls clfloor (which library?) and includes
> an argument 1.to_r (to_r from rational.rb).
>
> Len Lawrence

That's weird.

Looks like divmod is somehow confused on some machines....

On my Mac (ruby 1.8.6 (2007-03-13 patchlevel 0) [powerpc-
darwin8.9.0]):

irb(main):045:0> (14.9/24.0).divmod(1.0/24)
=> [13, 0.0375]


On my Linux box (ruby 1.8.5 (2006-12-04 patchlevel 2) [i386-linux]):

irb(main):002:0>  (14.9/24.0).divmod(1.0/24)
=> [14, 0.0375]
irb(main):003:0>