IBM's AMERICA architecture for the Risc System/6000

[Jim Salter]

I hate to say this, but the correct name of the floating-point archicture
for the RISC System/6000 is AMERICA.  The "R" word is one of those internal
code words that shouldn't have made it out, but did.  It's like people
constantly referring to the second-generation SPARC chips from Sun - calvin.

It's not only inappropriate after release, but just plain wrong.

In the meantime, let me point out that the original version (i.e. initial
release) of AIX 3.1 did not allow traps though that capability is
available in hardware.  We knew this, but could not incorporate it
consistently in a reasonable time frame.  So, the next best thing was to
provide the user with the ability to note exceptions in the FPSCR (Floating
Point Status and Control Word) through the routines fp_*_flag() as defined
in <fpxcp.h>.  The problem with this, of course, was that the user would
have to place these around all their potential problem areas.  And, even with
heavy pipelining and potential for zero-cycle branching available, this
is not without significant penalty.  Though probably not as much as the
trapping in hardware (as noted in the IBM JRD article).

Rest assured, this will be addressed soon.  And in a manner that is
hopefully consistent both with what's out there, what IEEE 754/854
defines, and where it looks like NCEG is heading.

jim/jsalter