fpsttest (opr #80)

[Mike B.]

Today I’ve played around with the undocumented opcode fpsttest (opr
#80).

It stores 3 words into memory

word[ Areg ] = FPL
word[ Areg @ 1 ] = FPH
word[ Areg @ 2 ] = FPS

FPH is the upper 32 bit of a REAL64
FPL is the lower 32 bit of a REAL64

for REAL32 the bits are a little bit scattered

s...sign
e...exp
m...mantissa

FPH: High

3 2 1 0
10987654321098765432109876543210
64 seeeeeeeeeeemmmmmmmmmmmmmmmmmmmm
32 s___eeeeeeeemmmmmmmmmmmmmmmmmmmm

FPL: Low

3 2 1 0
10987654321098765432109876543210
64 mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
32 mmm_____________________________

FPS: Status

Bit31 is a copy of FPH(31)
1 negative
0 not negative

Bit20 is a copy of not FPH(20) ??
1 even exp ??
0 odd exp ??

Bit19 sn/db
1 single (float)
0 double

Bit8+Bit7 rounding
00 rz
01 rn
10 rp
11 rm

Bit3
0 zero
1 not zero

The first fpsttest pushes FA, the second FB and the third FC. Rounding
bits of FB and FC are always rn. But I'm unable to locate the
FP_ErrorFlag. Any ideas or hints?

-Mike