Subject: bug#26259: closed (Re: bug#26259: ~f SRFI-19 format broken for small nanoseconds values)

From: [email-masked] (GNU bug Tracking System)
Date: Wed, 19 Apr 2017 13:51:02 +0000

Your bug report

#26259: ~f SRFI-19 format broken for small nanoseconds values

which was filed against the guile package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to [email-masked].

-- 
26259: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=26259
GNU Bug Tracking System
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Subject: Re: bug#26259: ~f SRFI-19 format broken for small nanoseconds values
From: Andy Wingo <[email-masked]>
To: Zefram <[email-masked]>
Cc: [email-masked]
Date: Wed, 19 Apr 2017 15:50:47 +0200
List-Id: <debbugs-submit.debbugs.gnu.org>

On Sun 26 Mar 2017 04:00, Zefram <[email-masked]> writes:

> scheme@(guile-user)> (date->string (make-date 550000 56 34 12 26 3 2017 0) "~f")
> $2 = "56.5e-4"

Thanks for the report.  Fixed in the the fix for #26260; added the test
case anyway.  Cheers.

Andy

Subject: ~f SRFI-19 format broken for small nanoseconds values
From: Zefram <[email-masked]>
To: [email-masked]
Date: Sun, 26 Mar 2017 03:00:50 +0100
List-Id: <debbugs-submit.debbugs.gnu.org>

The ~f format specifier in SRFI-19's date->string function is supposed
to produce a decimal string representation of the seconds and nanoseconds
portions of a date together:

scheme@(guile-user)> (use-modules (srfi srfi-19))
scheme@(guile-user)> (date->string (make-date 550000000 56 34 12 26 3 2017 0) "~f")
$1 = "56.55"

but it screws up for nanoseconds values in the range (0, 1000000), i.e.,
for any time that lies strictly within the first millisecond of a second:

scheme@(guile-user)> (date->string (make-date 550000 56 34 12 26 3 2017 0) "~f")
$2 = "56.5e-4"

Looks like the fractional seconds value is being formatted through a
mechanism that is not suitable for this purpose, which uses exponent
notation for sufficiently small values and thereby surprises the
date->string code.  Note that just assembling the seconds+fraction value
and putting the whole thing through the same formatter, as opposed to
putting the fractional part through on its own, would fix the above test
cases, and any others with non-zero integer seconds, but would leave
the bug unfixed for the case where the integer seconds value is zero.
Fixing this requires not using any formatting mechanism that would ever
resort to exponent notation for values in the relevant range.

-zefram