[armedbear-devel] bug in format ~f

Carlos Ungil carlos.ungil at gmail.com
Sun Mar 31 11:14:50 UTC 2013


comparing output from different implementations I've found the following
(minor) bug:

> (format t "~,2f" 0.999)
1.0 ;; should be 1.00

I think there is a problem here as well:

> (format t "~5f" 0.00000001)
.0000 ;; should print "  0.0"

Only SBCL gives the output I would expect, most implementations print
".0000" as ABCL does. From the HyperSpec "If the parameter d is
omitted, then there is no constraint on the number of digits to appear
after the decimal point. A value is chosen for d in such a way that as many
digits as possible may be printed subject to the width constraint imposed
by the parameter w and the constraint that ___no trailing zero digits may
appear in the fraction, except that if the fraction to be printed is zero,
then a single zero digit should appear after the decimal point___ if
permitted by the width constraint." This problem appears only when the
value is close to zero, otherwise the output is fine:

> (format t "~5f" 1.00000001)
  1.0 ;; OK

I guess those zero digits are not considered trailing because there is no
non-zero digit before but I think the specification still requires the
fraction to be printed with a single zero digit after the decimal point.


Carlos Ungil
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