# DateTime irrationality **URL:** \ **Category:** Ruby\ **Created:** [August 4, 2007, 2:41pm UTC](https://www.ruby-forum.com/t/datetime-irrationality/111258 "2007-08-04T14:41:22Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![tarazed](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ed8c4c/32.png) [@tarazed](https://www.ruby-forum.com/u/tarazed)\ **Post date:** [August 4, 2007, 2:41pm UTC](https://www.ruby-forum.com/t/datetime-irrationality/111258/1 "2007-08-04T14:41:22Z")
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 L. ---
**Author:** ![tarazed](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ed8c4c/32.png) [@tarazed](https://www.ruby-forum.com/u/tarazed)\ **Post date:** [August 4, 2007, 3:58pm UTC](https://www.ruby-forum.com/t/datetime-irrationality/111258/2 "2007-08-04T15:58:27Z")
Len L. 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). Just a matter of curiosity as an avid astronomer, what are you working on? 😉 I have a few astro related projects I’m working on. I started using Ruby but I fear it might be a little slow compared to others in some of the operations I’m performing (looking up star data from the TychoII catalog). What are your experiences? I considered using inline C but it’s a can of worms I haven’t dared open yet (based primarily on the fact I’m stuck on a Windows machine for development). Anyways, I just thought it was cool to see someone else waxing astro with ruby 😉 Cliff ---
**Author:** ![tarazed](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ed8c4c/32.png) [@tarazed](https://www.ruby-forum.com/u/tarazed)\ **Post date:** [August 4, 2007, 5:36pm UTC](https://www.ruby-forum.com/t/datetime-irrationality/111258/3 "2007-08-04T17:36:38Z")
On Sat, 04 Aug 2007 22:57:22 +0900, Cliff R. wrote: > — quoted text purged ----- > Anyways, I just thought it was cool to see someone else waxing astro > with ruby 😉 Will reply directly Cliff as it is a bit off-topic. Len ---
**Author:** ![tarazed](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ed8c4c/32.png) [@tarazed](https://www.ruby-forum.com/u/tarazed)\ **Post date:** [August 5, 2007, 4:21am UTC](https://www.ruby-forum.com/t/datetime-irrationality/111258/4 "2007-08-05T04:21:19Z")
On Aug 4, 8:35 am, “Len L.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > class Stime > sprintf( “%02d:%02d:%06.3f”, c[0],c[1],c[2] ) > > 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 L. 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\> ---
**Author:** ![tarazed](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ed8c4c/32.png) [@tarazed](https://www.ruby-forum.com/u/tarazed)\ **Post date:** [August 5, 2007, 11:05pm UTC](https://www.ruby-forum.com/t/datetime-irrationality/111258/5 "2007-08-05T23:05:45Z")
On Sun, 05 Aug 2007 02:18:57 +0000, georgebudd wrote: That’s weird. > Looks like divmod is somehow confused on some machines… > > 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\> I am using ruby 1.8.5 (2006-08-25) [x86\_64-linux-gnu] For now I shall use a workaround. Thanks ---
**Author:** ![tarazed](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ed8c4c/32.png) [@tarazed](https://www.ruby-forum.com/u/tarazed)\ **Post date:** [August 5, 2007, 11:07pm UTC](https://www.ruby-forum.com/t/datetime-irrationality/111258/6 "2007-08-05T23:07:46Z")
On Sat, 04 Aug 2007 22:57:22 +0900, Cliff R. wrote: > Anyways, I just thought it was cool to see someone else waxing astro > with ruby 😉 Sorry Cliff - my message to your gmail account bounced. This happens a lot. IP not authorized to access server directly - use SMTP relay of ISP. Haven’t a clue.