J3/14-220r1
To:      J3
From:    Nick Maclaren/Malcolm Cohen
Subject: Interpretation of values of type C_BOOL
Date: 2014 October 13


1. Introduction

This paper answers the questions raised in 14-220.


2. Questions and answers

Q1. If a Fortran variable of type LOGICAL(C_BOOL) is passed to a C
    function, is the Fortran processor required to represent
    .TRUE._C_BOOL by all bits zero except the one required bit?

A1. The requirements for LOGICAL(C_BOOL) are that .TRUE._C_BOOL shall have
    the same internal representation as (_Bool)1.  This follows from the
    interoperability requirements and the canonical truth values, and will
    be clarified (i.e. explicitly stated) in F2015.

Q2. If a processor and its companion processor support a negative integer
    zero, is the Fortran processor required to represent .FALSE._C_BOOL by
    all bits zero?

A2. The requirements are that .FALSE._C_BOOL shall have the same internal
    representation as (_Bool)0.  This will be clarified in F2015.

Q3. Is a companion processor allowed to return a non-zero value other than
    all bits zero except the least significant as an object of type
    LOGICAL(C_BOOL)?  And, if it allowed to, is a Fortran processor
    required to treat it as equivalent to .TRUE._C_BOOL?

A3. The only acceptable values of type LOGICAL are .TRUE._C_BOOL and
    .FALSE._C_BOOL; returning any other representation does not conform to
    the Fortran standard, as no interpretation is established (type LOGICAL
    only has two values).

Q4. Is a companion processor allowed to return a zero value other than with
    all bits zero as an object of type LOGICAL(C_BOOL)?  And, if it is
    allowed to, is a Fortran processor required to treat it as equivalent
    to .FALSE._C_BOOL.

A4. Same as A3.

===END===