R devel - Feb 2020 - round(x, dig) [was "Development version of R fails tests .."]

I?disagree?with?what?is?assessed?as?"correct"?in?vignette?of?package?'round'.

With
x?<-?9.18665
,?what?is?actually?stored?in?'x'?is?a?number?that?is?slightly?larger?than?9.18665.?So,?as?said?in?the?vignette,?it?is?closer?to?9.1867?than?9.1866.

sprintf("%.4f",?x)
giving
"9.1867"
is?correct,?as?it?is?a?string?representing?the?_exact_?number?9.1867.

For?round(x,?4)?,?that?gives?number?and?cannot?return?9.1867?exactly,?I?still?think?that?a?binary?double?precision?number?closest?to?9.1867?should?be?returned.?My?principles:
-?Input?number?should?be?read?as?is,?should?be?treated?as?exact.
-?What?counts?is?what?the?exact?result?should?be.


------------
>>>>>?Hugh?Parsonage
>>>>>?????on?Sat,?8?Feb?2020?21:12:43?+1100?writes:
????>?The?only?observation?I?can?make?is?that?the?change?to
????>?round()?was?made?in?r77727?whereas?your?R-devel?appears?to
????>?be?r77715?(so?would?not?exhibit?the?fixed?behaviour).??My
????>?guess?is?that?there?was?a?perpetual?installation?failure
????>?after?r77715?but?that?the?test?folder?was?still?retrieved
????>?and?used.


????>?On?Sat,?8?Feb?2020?at?19:27,?Berwin?A?Turlach?<berwin.turlach?using?gmail.com>?wrote:
????>>
????>>?G'day?all,
????>>
????>>?I?have?daily?scripts?running?to?install?the?patched?version?of?the
????>>?current?R?version?and?the?development?version?of?R?on?my?linux?box
????>>?(Ubuntu?18.04.4?LTS).
????>>
????>>?The?last?development?version?that?was?successfully?compiled?and
????>>?installed?was?"R?Under?development?(unstable)?(2020-01-25?r77715)"?on
????>>?27?January.??Since?then?the?script?always?fails?as?a?regression?test
????>>?seems?to?fail.??Specifically,?in?the?tests/?subdirectory?of?my?build
????>>?directory?I?have?a?file?reg-tests-1d.Rout.fail?which?ends?with:
????>>
????>>?>?##?more?than?half?of?the?above?were?rounded?*down*?in?R?<=?3.6.x
????>>?>?##?Some?"wrong"?test?cases?from?CRAN?packages?(partly?relying?on?wrong?R?<=?3.6.x?behavior)
????>>?>?stopifnot(exprs?=?{
????>>?+?????all.equal(round(10.7775,?digits=3),?10.778,?tolerance?=?1e-12)?#?even?tol=0,?was?10.777
????>>?+?????all.equal(round(12345?/?1000,???2),?12.35?,?tolerance?=?1e-12)?#?even?tol=0,?was?12.34?in?Rd
????>>?+?????all.equal(round(9.18665,?4),????????9.1866,?tolerance?=?1e-12)?#?even?tol=0,?was??9.1867
????>>?+?})
????>>?Error:?round(10.7775,?digits?=?3)?and?10.778?are?not?equal:

????>>?Mean?relative?difference:?9.27902e-05
????>>?Execution?halted
????>>
????>>?This?happens?while?the?32bit?architecture?is?installed,??which?is?a?bit
????>>?surprising?as?I?get?the?following?results?for?the?last?installed
????>>?version?of?R's?development?version:
????>>
????>>?R?Under?development?(unstable)?(2020-01-25?r77715)?--?"Unsuffered?Consequences"
????>>?Copyright?(C)?2020?The?R?Foundation?for?Statistical?Computing
????>>?Platform:?x86_64-pc-linux-gnu/32?(32-bit)
????>>?[...]
????>>?>?round(10.7775,?digits=3)
????>>?[1]?10.778
????>>
????>>?and
????>>
????>>?R?Under?development?(unstable)?(2020-01-25?r77715)?--?"Unsuffered?Consequences"
????>>?Copyright?(C)?2020?The?R?Foundation?for?Statistical?Computing
????>>?Platform:?x86_64-pc-linux-gnu/64?(64-bit)
????>>?[...]
????>>?>?round(10.7775,?digits=3)
????>>?[1]?10.778
????>>
????>>
????>>?On?the?other?hand,?the?R?3.6.2?version,?that?I?mainly?use?at?the?moment,
????>>?gives?the?following?results:
????>>
????>>?R?version?3.6.2?(2019-12-12)?--?"Dark?and?Stormy?Night"
????>>?Copyright?(C)?2019?The?R?Foundation?for?Statistical?Computing
????>>?Platform:?x86_64-pc-linux-gnu/32?(32-bit)
????>>?[...]
????>>?>?round(10.7775,?digits=3)
????>>?[1]?10.777
????>>
????>>?and
????>>
????>>?R?version?3.6.2?(2019-12-12)?--?"Dark?and?Stormy?Night"
????>>?Copyright?(C)?2019?The?R?Foundation?for?Statistical?Computing
????>>?Platform:?x86_64-pc-linux-gnu/64?(64-bit)
????>>?[...]
????>>?>?round(10.7775,?digits=3)
????>>?[1]?10.777
????>>
????>>
????>>?So?it?seems?as?if?the?behaviour?of?round()?has?changed?between?R?3.6.2
????>>?and?the?development?version.??But?I?do?not?understand?why?this?test?all
????>>?of?a?sudden?failed?if?the?results?from?the?last?successfully?installed
????>>?development?version?of?R?suggest?that?the?test?should?be?passed.
????>>
????>>?Thanks?in?advance?for?any?insight?and?tips.
????>>
????>>?Cheers,
????>>?Berwin

Note?that?r77727?was?the?last?of?a?few?commits?I?made?related?to
dealing?with?R's?bug?report?PR#17668:
??https://bugs.r-project.org/bugzilla/show_bug.cgi?id=17668

which?itself?triggered?an?involved?dialogue,?mostly?online,
visible?at?the?PR's?URL?above.

It?lead?me?to?also?write?an?R?package?'round'?(in?order?to
compare?R?3.6.x?and?later's?round()?versions,?comparing?them?etc)
with?a?(not?entirely?polished)?package?vignette
that?explains?how?rounding?to?decimal?digits?is?not?at?all
trivial?and?why?and?how?I?ended?(*)?improving?R's
round(x,?digits)?algorithm?in?R-devel.

The?CRAN?version?of?the?package
????https://cran.r-project.org/package=round

????install.packages("round")

is?not?quite?current,?notably?its?vignette?isn't?and?so?I?have
mentioned?in?the?above?thread
(?https://bugs.r-project.org/bugzilla/show_bug.cgi?id=17668#c8?)
that?the?latest?version?of?the?vignette?is?also?available?as

?????https://stat.ethz.ch/~maechler/R/Rounding.html

You?can?install?and?load?the?devel?version?of?'round'?by

???remotes::install_gitlab("mmaechler/round")
???require("round")

and?then?look?a?bit?at?the?different?versions?of?round(.)??using

???example(roundX)

i.e.?using?round::roundX(x,?digits,?version)

For?those?who?read?so?far:??I'm?really?interested?in?getting
critical?(constructive)?feedback?and?comments?about?what?I've
written?there?(in?the?bugzilla?report,?and?the?package?vignette).
It?seems?almost?nobody?till?now?has?had?much?interest?and?time?to?delve
into?the?somewhat?intriguing?issues.

Best?regards,
Martin?Maechler
ETH?Zurich?and?R?Core?team