GNU bug report logs - #26259
~f SRFI-19 format broken for small nanoseconds values

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Zefram <zefram <at> fysh.org>
Subject: bug#26259: closed (Re: bug#26259: ~f SRFI-19 format broken for
 small nanoseconds values)
Date: Wed, 19 Apr 2017 13:51:02 +0000

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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 26259 <at> debbugs.gnu.org.

-- 
26259: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=26259
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Andy Wingo <wingo <at> igalia.com>
To: Zefram <zefram <at> fysh.org>
Cc: 26259-done <at> debbugs.gnu.org
Subject: Re: bug#26259: ~f SRFI-19 format broken for small nanoseconds values
Date: Wed, 19 Apr 2017 15:50:47 +0200

On Sun 26 Mar 2017 04:00, Zefram <zefram <at> fysh.org> 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

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From: Zefram <zefram <at> fysh.org>
To: bug-guile <at> gnu.org
Subject: ~f SRFI-19 format broken for small nanoseconds values
Date: Sun, 26 Mar 2017 03:00:50 +0100

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

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