An efficient algorithm for ray casting of CSG animation frames

This paper presents a new algorithm to generate ray-cast CSG animation frames. We consider sequences of frames where only the objects can move; in this way, we take advantage of the high screen area coherence of this kind of animation. A new definition of bounding box allows us to reduce the number of pixels to be computed for the frames after the first. We associate a CSG subtree and two new flags, denoting if the box has changed in the current frame and if it will change in the next frame, with each box. We show with three examples the advantages of our technique when compared with an algorithm which entirely renders each frame of an animation. Intersections with CSG objects may be reduced to about one-fifth, while the rendering may be computed up to four times faster for the test sequences. © 1998 John Wiley & Sons, Ltd.     

Some properties of timed token medium access protocols

Timed-token protocols are used to handle, on the same local area network, both real-time and non-real-time traffic. The authors analyze this type of protocol, giving worst-case values for the throughput of non-real-time traffic and the average token rotation time. Results are obtained for synchronous traffic generated according to a generic periodic pattern under heavy conditions for non-real-time traffic and express not only theoretical lower bounds but values deriving from the analysis of some real networks. A model which addresses the asynchronous overrun problem is presented. The influence of introducing multiple priority classes for non-real-time traffic on the total throughput of this type of message is shown. It is also shown that the differences between the values obtained under worst-case assumptions are close to those obtained under best-case assumptions; the method may therefore be used to provide important guidelines in properly tuning timed-token protocol parameters for each specific network installation     

Selection of token holding times in timed-token protocols

Minimum requirements for the high-priority token holding time (HPTHT) in a network using timed token access protocols (such as IEEE 802.4 and FDDI) are derived in order to ensure that the throughput of synchronous messages is no lower than the amount of traffic generated for that class. The minimal value is essential in order to avoid unbounded queue length for the synchronous class as well as to achieve high network responsiveness. The results have been obtained for synchronous messages generated according to a generic periodic pattern with no constraint for the shape and for the period of the pattern. The manner in which the theoretical results obtained can be used to tune the network performance is also shown     

Radix-8 division with over-redundant digit set

We present a radix-8 divider that uses an over-redundant digit set for the quotient in order to obtain simple digit selection rules. We show that the proposed enlarged set of values for the quotient digit does not lead to increases both in the complexity and the delay of the adder required to update the remainder, with respect to similar solutions, since the values allowed for the quotient digit have been selected carefully. The digit selection process is subdivided into two concurrent steps, each one making reference to a secondary digit set and the resulting implementation can be cheaper and faster than other units which do not use over-redundant digit sets. A performance analysis estimates a speed improvement from 25% to 35% with respect to a radix-8 architecture by Fandrianto, and from 21% to 30% with respect to a radix-4 architecture with prescaling, presented by Ercegovac and Lang. As required from the IEEE 754 floating point standard, the proposed algorithm features the correct remainder of the division.     

Optimal absolute error starting values for Newton-Raphson calculation of square root

The problem of obtaining optimal starting values for the calculation of square root using Newton-Raphson's Method is considered. This paper presents the best starting values theory in order to optimize the maximum absolute error after a given number of iterations. Two different methods are shown, and a third, which can be considered as a mixture of the previous two, is briefly discussed. The approach combines analytical and numerical methodologies, which gives more interesting results on the main characteristics of the behavior of the absolute error for different initializations. A comparison table between the traditional optimal relative error results and the absolute error ones is provided.     

Parallel algorithm for image rendering and its implementation

The authors present a parallel algorithm for fast rendering. A set of zones which can be concurrently processed is identified; this set is split into a number of subsets equal to the number of available processors. Each processor renders, in parallel with the others, a zone of its set