bfloat16 in anticipation for hardware implementation.

[srinathv]

In light of possible hardware coming to the market with bfloat16 implemented what is the desire for the fortran community to support bfloat16? If not in the standard, is there a preferred way to approximate (or downcast)?

[certik]

@srinathv thanks a lot for the proposal. Note that it's a duplicate of #3.