To: J3                                                     J3/19-221
From: Tom Clune
Subject: BFLOAT16 variant of REAL16 representation
Date: 2019-September-24
Reference:   19-139r1

I. Introduction

New generations of processors are now providing half-precision
floating point capabilites that often provide significant performance
advantages over typical precisions.  While such capabilities must be
used carefully, various applications have now demonstrated useful
results.  In particular, machine learning algorithms can often exploit
such hardware capabilities in a robust fashion.

Paper 19-139r1 has already introduced a new REAL16 kind that partially
addresses this application space, but an increasingly populer
representation in the machine learning world is BFLOAT16.  This
representation sacrifices mantissa for an expanded exponent range.

II.  Use case

Enable portable development of applications that can exploit
increasingly commonly available BFLOAT16 hardware capabilities.  This
is particularly relevant to machine learning.

III. Rough requirement:

Expand iso_fortran_env to include BFLOAT16.  If, for any of these
constants, the processor supports more than one kind of that size, it
is processor dependent which kind value is provided.