sentences:  The encoding of "lzcnt" is similar enough to "bsr" (bit scan reverse) that if "lzcnt" is performed on a CPU not supporting it such as Intel CPU's prior to Haswell, it will perform the "bsr" operation instead of raising an invalid instruction error despite the different result values of "lzcnt" and "bsr".Trailing zeros can be counted using the "bsf" (bit scan forward) or "tzcnt" instructions.The SSE4a instruction group was introduced in AMD's Barcelona microarchitecture.