Re: "Double Precison" Keywords?

In article <ihnd6b$avp$1@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
glen herrmannsfeldt <gah@xxxxxxxxxxxxxxxx> wrote:
robin <robin51@xxxxxxxxxxxxxxxxxx> wrote:

The DXR instruction didn't exist, so they couldn't have found
that it was used rarely.
More likely., they probably were pushed for time, and didn't
develop the microcode in time for the 370.

Sigh. The DXR instruction DID exist, and was generated by the
compilers. It was trapped and emulated by a combination of the
Fortran and PL/I run-time systems and supervisor code. In a
much later design (the System/390) it was provided in hardware,
and then the compiled code invoked it.

For reasons that I never did understand, the assembler did not
originally have a DXR opcode, but had a macro that generated
the extended instruction code that was reserved for the actual
DXR instruction.

And it was FAR more likely space, rather than time, given the
complexity of the emulation code - and, yes, I have worked on it.

IBM has been pretty good at doing statistical analysis
instead of just guessing.

Extended precision floating point was developed for the 360/85.

And they allowed for a future implementation of DXR in hardware
at that stage.

As you probably know, Fortran and I think PL/I ran on machines
with no floating-point, by emulating all of those instructions
in the same way that DXR was emulated.


Regards,
Nick Maclaren.
.