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Communications of the ACM

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Synthetic chicken


Orderly enumeration of nonsingular binary matrices applied to text encryption

Nonsingular binary matrices of order N, i.e., nonsingular over the field {0, 1}, and an initial segment of the natural numbers are placed in one-to-one correspondence. Each natural number corresponds to two intermediate vectors …

A technique for isolating differences between files

A simple algorithm is described for isolating the differences between two files. One application is the comparing of two versions of a source program or other file in order to display all differences. The algorithm isolates differences …

Optimal conversion of extended-entry decision tables with general cost criteria

A general dynamic programming algorithm for converting limited, extended, or mixed entry decision tables to optimal decision trees is presented which can take into account rule frequencies or probabilities, minimum time and/or …

List processing in real time on a serial computer

A real-time list processing system is one in which the time required by the elementary list operations (e.g. CONS, CAR, CDR, RPLACA, RPLACD, EQ, and ATOM in LISP) is bounded by a (small) constant. Classical implementations of …

Secure communications over insecure channels

According to traditional conceptions of cryptographic security, it is necessary to transmit a key, by secret means, before encrypted massages can be sent securely. This paper shows that it is possible to select a key over open …

Assembling code for machines with span-dependent instructions

Many modern computers contain instructions whose lengths depend on the distance from a given instance of such an instruction to the operand of that instruction. This paper considers the problem of minimizing the lengths of programs …

A data structure for manipulating priority queues

A data structure is described which can be used for representing a collection of priority queues. The primitive operations are insertion, deletion, union, update, and search for an item of earliest priority.

Economical encoding of commas between strings

A method for insertion of delimiters between strings without using new symbols is presented. As the lengths of the strings increase, the extra cost, in terms of prolongation, becomes vanishingly small compared to the lengths  …

Generating beta variates with nonintegral shape parameters

A new rejection method is described for generating beta variates. The method is compared with previously published methods both theoretically and through computer timings. It is suggested that the method has advantages in both …

ACM forum: for and against the stand on Sheharansky