Jim writes:

Interestingly enough, V9 SPARC has a population count (number of bits set in word) instruction that was put in specificly at the request of No Such Agency.

Does anybody have a good idea what applications this is useful for? My first thought is that it's a very quick way to do linear error detection codes, since this instruction directly computes the Hamming weight of a code word. I can also see it being useful to detect correlations between sequences, such as a trial random stream and a known pseudorandom number generator. One would XOR the streams together and then count bits to calculate a correlation frequency. Other ideas? Eric

In <9302212232.AA12362@versant.com>, henry strickland writes: |> # From cypherpunks-request@toad.com Sun Feb 21 14:14:43 1993 |> # |> # Does anybody have a good idea what applications this is useful for? |> |> The old CDC CYBER machines had population count in its instruction |> set. Perhaps some scientific-type programmers would know what they |> used it for. The CYBER did not have a lot of instructions -- they |> were pretty practical about what they put in. i.e. != VAX More precedent: DG Eclipses have a COB (COunt Bits) instruction. Interestingly enough, there seems to be no such instruction in the VAX (This from R'ingTFM. I have pitifully little VAX experience.) ^ / ------/---- cp@jido.b30.ingr.com (Craig Presson) / /

...

Interestingly enough, there seems to be no such instruction in the VAX ...

but i believe the vax has ffs (find first set) instruction, which seems to have similar uses (whatever they may be).

peter

But that's not a population count (all bits set count) instruction. In the Motorola 68020/30/40, there's BFFFO, for Bit Field Find First One, if anyone was curious about 'find first set' instructions. Might as well mention that the 386/486 have BSF and BSR, Bit Scan Forward and Reverse, but now we're just getting into run-of-the-mill bit manipulation.