`bsr` and `bsf` have "undefined" results on a zero argument in Intel's documentation. In AMD's documentation however, the destination is supposed to be "unchang

`bsr` and `bsf` have "undefined" results on a zero argument in Intel's documentation. In AMD's documentation however, the destination is supposed to be "unchanged". What is unusual is that the 32-bit flavours of these instructions leave the upper 32 bits unchanged, whereas other 32-bit integer instructions write zeroes there even if the lower bits in the destination are unchanged. Perhaps Intel intends to make these instructions zero-extend in the future ... or does there exist some processor (from Intel or someone else) that zero-extends?