[cctalk] Re: Minicomputer front panel.

[Paul Koning via cctalk]

> On Sep 23, 2022, at 2:14 PM, Randy Dawson via cctalk <cctalk@classiccmp.org> 
> wrote:
> 
> On the top secret number cruching....
> 
> The Cray had an instruction called 'population count'
> 
> asked for by the NSA.
> 
> The number of bits on in a word, not sure what this was used for.

Cray did?  I didn't know that.  It first appeared in the CDC 6600, and yes, 
according to rumor at the request of NSA.  I can imagine it being used for 
statistical analysis of character patterns.

A non-classified example of its use is in the PLATO system for "fuzzy string 
matching".  PLATO needed to be able to recognize student answers that were 
correct but misspelled; it would do that, roughly speaking, by taking the 
difference of the expected string and the actual input and running population 
count on that.  A difference of less than n bits would be defined as a 
misspelled match.

        paul