Hi
I have the following three question about mul:

1.How does the soft multiplication implemented in gcc?

2.How many instruction periods the soft multiplication costs?

3.How many instruction periods the hard multiplication costs?

Could someone explain to me?

Thanks and Regards

* Liu Zhigang (305liuzg@163.net) wrote:

you enable it in -msoft-mul, it's implemented in gcc/config/or32/or32.S



many. ;) don't know really, just look at the implementation.



1.

regards,
p.

I wonder if the hard-multiplication would cost only one period to
execute... it is usually implemented as a multicycle operation so as to
avoid a large hardware multiplier. Although for all practical matters
it can start one multiply operation every cycle but may finish in 5,10,
20 cycles, depending on the silicon implementation. Ideally it would be
1 but I wouldn't pay the difference in sillicon as multiplies are not
used that often so that we can not wait some cycles till it finishes,
but I guess that's the compiler's problem... or am I mistaken? anybody
can shed some light on this, please?



gcc/config/or32/or32.S