On 18.10.2011 11:43, Manu wrote:
On 18 October 2011 12:12, Don <[email protected]
<mailto:[email protected]>> wrote:
You mean bsr and bsf.
Unfortunately, there are some big problems with them. What is bsr(0) ?
True ;) .. but that's why the API needs to be defined and standardised.
On PowerPC it returns 32 (or 64), and the x86 version returns 2 values,
the position, and also a bool telling you if it was zero or not (useful
for loop termination)
Even worse -- Intel says that the position value of bsr(0) is undefined.
But AMD does define it, they say it's what was in the register before.
I think all hardware that I've seen is easy to factor into the win32
intrinsic api.
That would be nice. What do you think it should do for the zero case?
Note that on x86, one possibility is to do a bsr followed by a cmov, to
get the PowerPC semantics.
