On 23 October 2013 03:59, Tina Harriott <tina.harriott.m...@gmail.com> wrote: > On 11 August 2013 10:43, Tina Harriott <tina.harriott.m...@gmail.com> wrote: >> On Wed, Jul 24, 2013 at 7:28 PM, Glenn Fowler <g...@research.att.com> wrote: >>> >>> On Wed, 24 Jul 2013 19:02:39 +0200 Tina Harriott wrote: >>>> Here's one of my little tough problems which I am unable to solve >>>> myself, even after looking at the source code of ast-ksh. The problem >>>> below requires a good understanding how floating point numbers are >>>> implemented in computers. >>> >>>> I'm trying to prototype code and like to iterate over a small, linear >>>> area by using the C library function nextafter() to step forward the >>>> smallest possible distance between each step, and print the number of >>>> iterations needed to cover the distance between 4 and 4.000000000001: >>>> ksh -c 'float v ; integer iter ; for ((iter=0,v=4 ; v < 4.000000000001 >>>> && iter < 10000000; v=nextafter(v,4.000000000001))) ; do >>>> ((iter++));done;print $iter ' >>>> 2305843 >>> >>>> The result 2305843 is correct. >>> >>>> However, if I use typeset -E (or just typeset) to declare the variable >>>> v the loop runs forever, or in this case until it hits iter < 10000000 >>>> which I added as safeguard later: >>>> ksh -c 'typeset -E v ; integer iter ; for ((iter=0,v=4 ; v < >>>> 4.000000000001 && iter < 10000000; v=nextafter(v,4.000000000001))) ; >>>> do ((iter++));done;print $iter ' >>>> 10000000 >>> >>>> Can anyone explain this? >>> >>> float is an alias >>> this shows the alias definition >>> type float >>> which is >>> typeset -lE >>> this documents -l >>> typeset --?l >>> >>> so for your example >>> typeset -E >>> gave you a double v and >>> typeset -lE >>> would give you a "long double" v >> >> But why does nextafter() misbehave if I want to use a datatype smaller >> than "long double"? Accuracy is a good thing, but in this case we >> iterate too fine-grained, meaning the code should iterate over the >> smallest possible steps of a double, but not over the smallest >> possible steps of a long double. >> >> Tina >> -- >> Tina Harriott - Women in Mathematics >> Contact: tina.harriott.m...@gmail.com > > I am still running into this bug in ksh 20131010. Does it still take > long to have it fixed?
Is this going to be fixed in the next alpha? Tina -- Tina Harriott - Women in Mathematics Contact: tina.harriott.m...@gmail.com _______________________________________________ ast-users mailing list ast-users@lists.research.att.com http://lists.research.att.com/mailman/listinfo/ast-users
