Hi Emil, This is sort-of expected. MacRuby floats have less precision than MRI because we pack them as immediate values, for performance reasons. As a more generic issue, floating point arithmetic is almost never accurate. Laurent On Jun 5, 2010, at 9:59 AM, Emil Tin wrote:
hey, thanks for all the great work with macruby!
i'm experiencing a difference in floating point behaviour between mri and the latest macruby 0.7 nightly:
~$ ruby -v ruby 1.8.7 (2009-06-08 patchlevel 173) [universal-darwin10.0]
~$ ruby -e "z = 0.034228469425; puts Math.sqrt(z*z) < z" false
~$ ruby -e "z = 0.034228469424; puts Math.sqrt(z*z) < z" false
~$ macruby -v MacRuby 0.7 (ruby 1.9.2) [universal-darwin10.0, x86_64]
~$ macruby -e "z = 0.034228469425; puts Math.sqrt(z*z) < z" false
~$ macruby -e "z = 0.034228469424; puts Math.sqrt(z*z) < z" true
notice how that last script outputs true instead of false. also i'm seeing this difference with floats:
~$ ruby -e "puts 8.1" 8.1
~$ macruby -e "puts 8.1" 8.09999999999999
this difference is causing trouble because asin() might fail even when the input seems to be 1.0:
z = 0.034228469424 r = Math.sqrt z*z puts d = z/r # => 1.0 puts d>1.0 # false with mri, but true with macruby puts Math.asin d # => 1.5707963267949 with mri, but error with macruby (since d>1.0)
-emil
_______________________________________________ MacRuby-devel mailing list MacRuby-devel@lists.macosforge.org http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel