🚀 go-pugleaf

rodd@dasys1.UUCP (Rod Dorman) writes:
> As many compiler writers have found in the past and I'm sure many will
> rediscover in the future, this only works for positive values.  Try
> shifting -1 and you'll get -1 as a result, *not* zero as one would expect.

I think the problem is that shifting always rounds down, as opposed
to towards zero, like we expect.  So even in cases where you have a
signed, unkown value to divide, it would probably still be more
effecient to inline code.

So, when dividing a signed value, x, by a power of two, y:

if(x<0 && (x&(y-1))!=0)
    x|=y; /* pre-round negative numbers */
x>>=log2(y);

Which isn't quite as bad as it looks, since y is a known constant
power of two.

-Miles