this paper trade-offs among certain computational factors in hash coding are analyzed. The paradigm problem considered is that of testing a series of messages one-by-one for membership in a given set of messages. Two new hash- coding methods are examined and compared with a particular conventional hash-coding method. The computational factors considered are the size of the hash area (space), the time required to identify a message as a nonmember of the given set (reject time), and an allowable error frequency

An automated analysis of all reachable states in a distributed system can be used to trace obscure logical errors that would be very hard to find manually. This type of validation is traditionally performed by the symbolic execution of a finite state machine (FSM) model of the system studied. The application

Using a trace of address references, we compared the efficiency of several different hashing functions, such as cyclic redundancy checking (CRC) polynomials, Fletcher checksum, folding of address octets using the exclusive-or operation, and bit extraction from the address. Guidelines are provided for determining the size of hash mask required to achieve a specified level of performance. 1 INTRODUCTION The trend toward networks becoming larger and faster, addresses becoming larger, has impelled a need to explore alternatives for fast address recognition. This problem is actually a special case of the general problem of searching through a large data base and finding the information associated with a given key. For example, Datalink adapters on local area networks (LAN) need to recognize the multicast destination addresses of frames on the LAN. Bridges, used to interconnect two or more LANs, have to recognize the destination addresses of every frame and decide quickly whether to receive...

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This paper studies the four basic types of algorithm that, over the last ten years, have been developed for the automated validation of the logical consistency of data communication protocols. The algorithms are compared on memory usage, CPU time requirements, and the quality, or coverage, of the search for errors. It is shown that the best algorithm, according to above criteria, can be improved further in a significant way, by avoiding a known performance bottleneck. The algorithm derived in this manner works in a fixed size memory arena (it will never run out of memory), it is up to two orders of magnitude faster than the previous methods, and it has superior coverage of the state space when analyzing large protocol systems. The algorithm is the first for which the search efficiency (the number of states analyzed per second) does not depend of the size of the state space: there is no time penalty for analyzing very large state spaces. The effectiveness of the new algorith...

Most computer architectures are moving to 64-bit virtual address spaces. We first discuss how this change impacts conventional linear, forwardmapped, and hashed page tables. We then introduce a new page table data structure—clustered page table—that can be viewed as a hashed page table augmented with subblocking. Specifically, it associates mapping information for several pages (e.g., sixteen) with a single virtual tag and next pointer. Simulation results with several workloads show that clustered page tables use less memory than alternatives without adversely affecting page table access time. Since physical address space use is also increasing, computer architects are using new techniques—

In these notes we will review the automata-theoretic verification method and propositional linear temporal logic, with specific emphasis on their potential application to distributed software verification. An important

Over the past ten years much research effort has been expended in attempting to build systems which support orthogonal persistence. Such systems allow all data to persist for an arbitrary length of time, possibly longer than the creating program, and support access and manipulation of data in a uniform manner, regardless of how long it persists. Persistent systems are usually based on a persistent store which provides storage for objects. Most existing persistent systems have been developed above conventional architectures and/or operating systems. In this paper we argue that conventional architectures provide an inappropriate base for persistent object systems and that we must look towards new architectures if we are to achieve acceptable performance. The examples given are based on the Monads architecture which provides explicit hardware support for persistence and objects. 1. INTRODUCTION Over the past ten years much research effort has been expended in attempting to build systems w...

Scalable storage architectures allow for the addition or removal of disks to increase storage capacity and bandwidth or retire older disks. Assuming random placement of data blocks across multiple disks of a disk array, our optimization objective is to redistribute a minimum number of blocks after disk scaling. In addition, a uniform distribution, and hence a balanced load, should be ensured after redistribution. Moreover the redistributed...

Sorting and hashing are two completely different concepts in computer science, and appear mutually exclusive to one another. Hashing is a search method using the data as a key to map to the location within memory, and is used for rapid storage and retrieval. Sorting is a process of organizing data from a random permutation into an ordered arrangement, and is a common activity performed frequently in a variety of applications. Almost all conventional sorting algorithms work by comparison, and in doing so have a linearithmic greatest lower bound on the algorithmic time complexity. Any improvement in the theoretical time complexity of a sorting algorithm can result in overall larger gains in implementation performance. A gain in algorithmic performance leads to much larger gains in speed for the application that uses the sort algorithm. Such a sort algorithm needs to use an alternative method for ordering the data than comparison, to exceed the linearithmic time complexity boundary on algorithmic performance. The hash sort is a general purpose non-comparison based sorting algorithm by hashing, which has some interesting features not found in conventional sorting algorithms. The hash sort asymptotically outperforms the fastest traditional sorting algorithm, the quick sort. The hash sort algorithm has a