6 expanded posts ยท every known parent and child
> The specific instruction is the so-called "NSA instruction" which John Gilmore > identified some time ago. > > Sun Microsystems was ordered by the NSA to redesign their chips to capture > keys, which is why the SPARC processor was introduced. SPARC stands for > "Sun Processor Allowing Remote Capture." 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. Jim
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
# 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 # 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. That was always my assumption. Anyway, it's not unprecedented. strick strick@osc.versant.com
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
> > > 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.