basic formats

[Vincent Lefevre <vincent@xxxxxxxxxx>]

Hi,

The standard says:

  2.1.4 basic format: One of five floating-point representations,
  three binary and two decimal, whose encodings are specified by this
  standard, and which can be used for arithmetic. One or more of the
  basic formats is implemented in any conforming implementation.

and

  3.1.1 Formats

  This clause defines floating-point formats, which are used to
  represent a finite subset of real numbers (see 3.2). Formats are
  characterized by their radix, precision, and exponent range, and
  each format can represent a unique set of floating-point data
  (see 3.3).

  All formats can be supported as arithmetic formats; that is, they
  may be used to represent floating-point operands or results for
  the operations described in later clauses of this standard.

  Specific fixed-width encodings for binary and decimal formats
  are defined in this clause for a subset of the formats (see 3.4
  and 3.5). These interchange formats are identified by their size
  (see 3.6) and can be used for the exchange of floating-point
  data between implementations.

  Five basic formats are defined in this clause:
    -- Three binary formats, with encodings in lengths of 32, 64,
       and 128 bits.
    -- Two decimal formats, with encodings in lengths of 64 and
       128 bits.
  Additional arithmetic formats are recommended for extending these
  basic formats (see 3.7).

This is not clear. It seems that both binary16 and decimal32 satisfy
the conditions of the "basic format" definition: their encodings are
specified and they can be used for arithmetic (second paragraph of
3.1.1). In some drafts, they were declared as "storage formats". but
this notion seems to have disappeared. So, what is their status?

-- 
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.org/>
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Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)