Afternoon all.
I'm puzzled again. I'm writing an article on the use of the maths packags in
QDOSMSQ for our esteemed QL Toady magazine and I've hit a small problem that,
for the life of me, I can't figure out.
I was explaining the SAVE and LOAD op codes for RI_EXEC and RI_EXECB where the
top of stack floating point value is saved to a variables area at (A6,A1.L) or
a new TOS is created by loading back from said area. The op codes for save are
even in the range $32 to $FF and the load op codes are odd in the same range.
Save with $32 and load the same value back with $33, save with $34 and load
with $35 and so on.
I was trying to explain where exactly the 6 bytes of the FP number are loaded
from and saved to, so I decided to have a look at the code in the SMSQE 3.1.2
source, and I found the qa_op and qa_mop routines, tracing through these I
basically found the following (in file smsq\qa\op.asm) :
6 bytes are saved and loaded to and from the address given by (A6.L + A4.L +
D0.W) where D0.W is simply the op code in the range £32 to $FF with bit zero
cleared (ie even).
Now I had assumed that I could save one FP using code $32 and another using op
code $34 and so on, but the source appears to indicate that I will overwrite
part of my $32 saved FP with part of my $34 saved FP.
Not only this, but I'm effectively wasting the $32 bytes at the start of my
buffer at (A6,A4.L) because the lowest op code I can use is $32 and that writes
to my (buffer address + $32) to (buffer address + $37).
My next save would be to (buffer address + $34) to (buffer address + $39) - and
so on.
Is this a bug in SMSQE or am I missing something serios here.
What I was expecting is the load and saves to occur from (D0.W - $32) *6 bytes
on from the start of my buffer - this would allow me to save consecutive FP
values without corruption.
Anyone got any ideas ?
Here's the code :
;+++
; QL Arithmetic: do operation
;
; d0 cr operation code error return
; a1 c u pointer to arithmetic stack
; a4 c p pointer to (top of) variables area
; a6 base address
; status return standard
;---
qr_op
add.l a6,a1
add.l a6,a4
bsr.s qa_op
sub.l a6,a4
sub.l a6,a1
rts
;+++
; QL Arithmetic: do operation
;
; d0 cr operation code error return
; a1 c u pointer to arithmetic stack
; a4 c p pointer to (top of) variables area
; a6 base address
; status return standard
;---
qa_op
ext.w d0
cmp.w #qa.maxop,d0 ; operation?
bhi.s qao_ldst ; ... no
add.w d0,d0
add.w qao_tab(pc,d0.w),d0
jmp qao_tab(pc,d0.w) ; ... do it
qao_ldst
bclr #0,d0 ; load or store
beq.s qao_load
move.w (a1)+,(a4,d0.w)
move.l (a1)+,2(a4,d0.w) ; store
bra.s qao_ok
qao_load
move.l 2(a4,d0.w),-(a1) ; load
move.w (a4,d0.w),-(a1)
qao_ok
moveq #0,d0
rts
Cheers,
Norman.
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