i assumed the list of opcodes and short instruction descriptions was
correct, and that indeed, being a manly lot, the floating-point implementers
who wrote that section loftily regarded 32-bits as being the bare minimum for a `word',
and included decent 64-bits within the term.  (hence the reference to `short-integer'
for the 16-bit runts.)

still, in this case i think the

8.out 708: suicide: sys: fp: stack underflow fppc=0x1118 status=0x80a1 pc=0x0000118f

is saying stack underflow only because /sys/src/9/pc/main.c isn't reading the
status correctly, unless i'm getting the bits wrong myself compared to the handbook.
i think it's `inexact result (precision error)'.  0x40 is set for stack fault;
it's checking for (status & 0x30), although perhaps
(status & 0x30) == 0 was intended, to avoid masking other faults?
the exception flags are sticky.

that would be good because i couldn't see the incorrect stacking in
the 8c code.