🚀 go-pugleaf

In article <348a5a$dhs@haven.umd.edu>, Charles B. Cranston
<zben@ni.umd.edu> wrote:

> These are my first two assembly language programs on the power PC.
> dmult multiplies two 32 bit numbers to get a 64 bit result,
> ddiv divides a 32 bit number into a 64 bit number to get a 32 bit result.
> it probably needs to be protected from overflow...

> dmult   ;
>         MulLW   R6,R3,R4                ; Generate low word of result
>         StW     R6,4(R5)                ; Save result
>         MulHWU  R7,R3,R4                ; Generate high word of result
>         StW     R7,0(R5)                ; Save result
>         BLR                             ; Return to caller

  This code makes me curious about PPC assembly (I've read the manual and
a book on it, but I guess the details don't stick until you write some
code).  I would have thought that there would be some way to get the 64bit
value to an FP register and then write it out to memory, thus saving a
very expensive extra memory write operation.  Also, everything I know
about pipelining suggests that reorganizing the code as

MulLW   R6,R3,R4                ; Generate low word of result
MulHWU  R7,R3,R4                ; Generate high word of result
StW     R6,4(R5)                ; Save result
StW     R7,0(R5)                ; Save result

would be more efficient.  If anyone can spare the time to clue me in on
the finer points of PPC assembly, I'd appreciate it (not that I mind
programming in C/C++, but occasionally it seems somewhat inefficient...)

-- 

Brian Lowry