11-174
To: J3
From: John Reid and Thomas Henlich
Subject: Interp: G editing for reals
Date: 2011 June 09

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NUMBER: F08/xxxx
TITLE: G editing for reals
KEYWORDS: format, G editing
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

QUESTION:

1. Gw.d editing for a real value that is in the range (0.1,10**d) and
is not near an integer power of 10 uses F editing to produce exactly
the same value as E editing would produce with d significant digits and
the scale factor zero. For values in this range that are near an integer
power of 10, is it intended that F editing be used to produce exactly
the same value as E editing would produce with d significant digits and
the scale factor zero?

The rules in 10.7.5.2.2 usually have this effect, but the following
examples illustrate exceptions for rounding UP and to ZERO.
  i.
     print "(ru,g11.2)", -9.95
  or
     print "(rz,g11.2)", -9.95
  Here, 0PE11.2 editing would produce the output field -0.99E+01, which
  can be   represented as -9.9. However, the standard requires F7.0 to
  be used,   which gives the result -9. Note that the standard requires
     print "(rd,g11.2)", 9.95
  and
     print "(rz,g11.2)", 9.95
  to give the result 9.9.

  ii.
     print "(ru,0p,g11.2)", -99.5
  The standard requires 0PE11.2 editing to be used, which gives
  -0.99E+02. This is representable as -99.

  iii.
     print "(ru,0p,g11.2)", 99.
  The standard requires 0PE11.2 editing to be used, which gives
  0.99E+02. This is representable as 99.

Note that we use words "E editing with d significant digits and the
scale factor zero" instead of "0PEw.d editing" because there some rare
situations where 0PEw.d editing would fail but 0PEv.dEe with v>w and e>2
would work and produce an output field whose value can be represented
with F editing. Here are two examples:
     print "(g8.2)", 99.0
     print "(g110.2)", 0.99d100


2. COMPATIBLE and NEAREST modes of rounding differ only when the two
nearest representable values are equidistant from the given value. The
similarity appears not to be represented in the second table. What is
meant by "if the higher value is even"?

3. Why is no account taken of the effects when PROCESSOR_DEFINED
rounding is in effect? Why is no account taken of whether IEEE rounding
on conversions is supported (see 10.7.2.3.7 paragraph 4)?



ANSWER:

1. Yes, this was the intention and it would be clearer for the standard
to state this directly. It would also be easier for implementers to
implement.

2. If the standard is rewritten as proposed in the first answer, these
further problems would be resolved.

3. If the standard is rewritten as proposed in the first answer,
PROCESSOR_DEFINED rounding would be covered, as would the effect
of the processor not supporting IEEE rounding on conversions.


EDITS to 10-007r1:

[258:14-20] In 10.7.5.2.2, replace paragraph 4 by
"Otherwise, the method of representation in the output field depends
on the internal value being edited. Let k be the scale factor (10.8.5)
and let b be a blank character. Let N be the output field for E editing
with d significant digits and the scale factor zero and let s be its
exponent part unless the internal value is identically 0 in which case
let s be 1. For Gw.d editing, if s lies in the range 0 <= s <= d,
F(w-n).(d-s),n('b') editing where n=4 is used to represent N in the
output field; otherwise, kPEw.d editing is used to represent the
internal value. For Gw.dEe editing, if s lies in the range 0 <= s <= d,
F(w-n).(d-s),n('b') editing where n=e+2 is used to represent N in the
output field; otherwise, kPEw.dEe editing is used to represent the
internal value."


SUBMITTED BY: John Reid and Thomas Henlich

HISTORY: 11-xxx    m195  Submitted

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